第 14 章 Successive Refinement 逐步改进
# 第 14 章 Successive Refinement 逐步改进
Case Study of a Command-Line Argument Parser
This chapter is a case study in successive refinement. You will see a module that started well but did not scale. Then you will see how the module was refactored and cleaned.
本章研究一个逐步改进的案例。你将看到一个开始还不错，规模扩大后即出问题的模块。你还将看到这个模块是如何被重构得整洁起来的。
Most of us have had to parse command-line arguments from time to time. If we don’t have a convenient utility, then we simply walk the array of strings that is passed into the main function. There are several good utilities available from various sources, but none of them do exactly what I want. So, of course, I decided to write my own. I call it: Args.
我们中的大多数人都会遇到解析命令行参数的情况。如果没有就手的工具，就得遍历传入 main 函数的字符串数组。有一些不同来源的好工具，但没有一个是最符合要求的。所以，我当然要自己写一个。我把它叫做 Args。
Args is very simple to use. You simply construct the Args class with the input arguments and a format string, and then query the Args instance for the values of the arguments. Consider the following simple example:
Args 非常易于使用。你只要简单地用输入参数和格式化字符串构造 Args 类，再向 Args 实体询问参数值即可。看看下面的简单例子：
Listing 14-1 Simple use of Args
代码清单 14-1 Args 的简单用法
public static void main(String[] args) {
try {
Args arg = new Args(“l,p#,d*”, args);
boolean logging = arg.getBoolean(’l’);
int port = arg.getInt(’p’);
String directory = arg.getString(’d’);
executeApplication(logging, port, directory);
} catch (ArgsException e) {
System.out.printf(“Argument error: %s\n”, e.errorMessage());
}
}
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You can see how simple this is. We just create an instance of the Args class with two parameters. The first parameter is the format, or schema, string: “l,p#,d*.” It defines three command-line arguments. The first, -l, is a boolean argument. The second, -p, is an integer argument. The third, -d, is a string argument. The second parameter to the Args constructor is simply the array of command-line argument passed into main.
可以看到这有多简单。我们只是用两个参数创建了 Args 类的一个实体。第一个参数是格式字符串，或范式字符串：l,p#,d*。它定义了三个命令行参数。第一个，-l，是一个布尔值参数。第二个，-p，是一个整数参数。第三个，-d，是一个字符串参数。向 Args 构造器传入的第二个参数就是向 main 传入的命令行参数数组。
If the constructor returns without throwing an ArgsException, then the incoming command-line was parsed, and the Args instance is ready to be queried. Methods like getBoolean, getInteger, and getString allow us to access the values of the arguments by their names.
如果构造器正常返回，没有抛出 ArgsException 异常，则命令行参数已传入，Args 实体随时待命。使用 getBoolean、getInteger 和 getString 等方法，可以用参数名称获得参数值。
If there is a problem, either in the format string or in the command-line arguments themselves, an ArgsException will be thrown. A convenient description of what went wrong can be retrieved from the errorMessage method of the exception.
不管是格式化字符串或命令行参数出现问题，就会抛出一个 ArgsException 异常。可以从该异常的 errorMessage 中获得关于错误的描述。
# 14.1 ARGS IMPLEMENTATION Args 的实现
Listing 14-2 is the implementation of the Args class. Please read it very carefully. I worked hard on the style and structure and hope it is worth emulating.
代码清单 14-2 是 Args 类的实现。请仔细阅读。我在代码风格和结构上花了大力气，使之值得仿效。
Listing 14-2 Args.java
代码清单 14-2 Args.java
package com.objectmentor.utilities.args;
import static com.objectmentor.utilities.args.ArgsException.ErrorCode.*;
import java.util.*;
public class Args {
private Map<Character, ArgumentMarshaler> marshalers;
private Set<Character> argsFound;
private ListIterator<String> currentArgument;
public Args(String schema, String[] args) throws ArgsException {
marshalers = new HashMap<Character, ArgumentMarshaler>();
argsFound = new HashSet<Character>();
parseSchema(schema);
parseArgumentStrings(Arrays.asList(args));
}
private void parseSchema(String schema) throws ArgsException {
for (String element : schema.split(","))
if (element.length() > 0)
parseSchemaElement(element.trim());
}
private void parseSchemaElement(String element) throws ArgsException {
char elementId = element.charAt(0);
String elementTail = element.substring(1);
validateSchemaElementId(elementId);
if (elementTail.length() == 0)
marshalers.put(elementId, new BooleanArgumentMarshaler());
else if (elementTail.equals("*"))
marshalers.put(elementId, new StringArgumentMarshaler());
else if (elementTail.equals("#"))
marshalers.put(elementId, new IntegerArgumentMarshaler());
else if (elementTail.equals("##"))
marshalers.put(elementId, new DoubleArgumentMarshaler());
else if (elementTail.equals("[*]"))
marshalers.put(elementId, new StringArrayArgumentMarshaler());
else
throw new ArgsException(INVALID_ARGUMENT_FORMAT, elementId, elementTail);
}
private void validateSchemaElementId(char elementId) throws ArgsException {
if (!Character.isLetter(elementId))
throw new ArgsException(INVALID_ARGUMENT_NAME, elementId, null);
}
private void parseArgumentStrings(List<String> argsList) throws ArgsException {
for (currentArgument = argsList.listIterator(); currentArgument.hasNext(); ) {
String argString = currentArgument.next();
if (argString.startsWith("-")) {
parseArgumentCharacters(argString.substring(1));
} else {
currentArgument.previous();
break;
}
}
}
private void parseArgumentCharacters(String argChars) throws ArgsException {
for (int i = 0; i < argChars.length(); i++)
parseArgumentCharacter(argChars.charAt(i));
}
private void parseArgumentCharacter(char argChar) throws ArgsException {
ArgumentMarshaler m = marshalers.get(argChar);
if (m == null) {
throw new ArgsException(UNEXPECTED_ARGUMENT, argChar, null);
} else {
argsFound.add(argChar);
try {
m.set(currentArgument);
} catch (ArgsException e) {
e.setErrorArgumentId(argChar);
throw e;
}
}
}
public boolean has(char arg) {
return argsFound.contains(arg);
}
public int nextArgument() {
return currentArgument.nextIndex();
}
public boolean getBoolean(char arg) {
return BooleanArgumentMarshaler.getValue(marshalers.get(arg));
}
public String getString(char arg) {
return StringArgumentMarshaler.getValue(marshalers.get(arg));
}
public int getInt(char arg) {
return IntegerArgumentMarshaler.getValue(marshalers.get(arg));
}
public double getDouble(char arg) {
return DoubleArgumentMarshaler.getValue(marshalers.get(arg));
}
public String[] getStringArray(char arg) {
return StringArrayArgumentMarshaler.getValue(marshalers.get(arg));
}
}
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Notice that you can read this code from the top to the bottom without a lot of jumping around or looking ahead. The one thing you may have had to look ahead for is the definition of ArgumentMarshaler, which I left out intentionally. Having read this code carefully, you should understand what the ArgumentMarshaler interface is and what its derivatives do. I’ll show a few of them to you now (Listing 14-3 through Listing 14-6).
注意，你可以从上到下阅读这些代码，不用跳来跳去，也不用先看后面的部分。唯一需要先看的是 ArgumentMarshaler 的定义，这部分我有意省略了。仔细看这段代码，你应该能理解 ArgumentMarshaler 接口是什么，其派生类做什么。下面我将向你展示一部分（如代码清单 14-3 ～ 14-6 所示）。
Listing 14-3 ArgumentMarshaler.java
代码清单 14-3 ArgumentMarshaler.java
public interface ArgumentMarshaler {
void set(Iterator<String> currentArgument) throws ArgsException;
}
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Listing 14-4 BooleanArgumentMarshaler.java
public class BooleanArgumentMarshaler implements ArgumentMarshaler {
private boolean booleanValue = false;
public void set(Iterator<String> currentArgument) throws ArgsException {
booleanValue = true;
}
public static boolean getValue(ArgumentMarshaler am) {
if (am != null && am instanceof BooleanArgumentMarshaler)
return ((BooleanArgumentMarshaler) am).booleanValue;
else
return false;
}
}
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Listing 14-5 StringArgumentMarshaler.java
代码清单 14-5 StringArgumentMarshaler.java
import static com.objectmentor.utilities.args.ArgsException.ErrorCode.*;
public class StringArgumentMarshaler implements ArgumentMarshaler {
private String stringValue =
public void set(Iterator<String> currentArgument) throws ArgsException {
try {
stringValue = currentArgument.next();
} catch (NoSuchElementException e) {
throw new ArgsException(MISSING_STRING);
}
}
public static String getValue(ArgumentMarshaler am) {
if (am != null && am instanceof StringArgumentMarshaler)
return ((StringArgumentMarshaler) am).stringValue;
else
return "";
}
}
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The other ArgumentMarshaler derivatives simply replicate this pattern for doubles and String arrays and would serve to clutter this chapter. I’ll leave them to you as an exercise.
ArgumentMarshaler 的其他派生类以同样的模式处理 double 和 String 数组，一一列出反而阻碍行文。你可以练习自己实现它们。
One other bit of information might be troubling you: the definition of the error code constants. They are in the ArgsException class (Listing 14-7).
还有些信息可能会困扰你：错误码常量的定义。这些是在 ArgsException 类（代码清单 14-7）中定义的。
Listing 14-6 IntegerArgumentMarshaler.java
代码清单 14-6 IntegerArgumentMarshaler.java
import static com.objectmentor.utilities.args.ArgsException.ErrorCode.*;
public class IntegerArgumentMarshaler implements ArgumentMarshaler {
private int intValue = 0;
public void set(Iterator<String> currentArgument) throws ArgsException {
String parameter = null;
try {
parameter = currentArgument.next();
intValue = Integer.parseInt(parameter);
} catch (NoSuchElementException e) {
throw new ArgsException(MISSING_INTEGER);
} catch (NumberFormatException e) {
throw new ArgsException(INVALID_INTEGER, parameter);
}
}
public static int getValue(ArgumentMarshaler am) {
if (am != null && am instanceof IntegerArgumentMarshaler)
return ((IntegerArgumentMarshaler) am).intValue;
else
return 0;
}
}
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Listing 14-7 ArgsException.java
代码清单 14-7 ArgsException.java
import static com.objectmentor.utilities.args.ArgsException.ErrorCode.*;
public class ArgsException extends Exception {
private char errorArgumentId = '\0';
private String errorParameter = null;
private ErrorCode errorCode = OK;
public ArgsException() {
}
public ArgsException(String message) {
super(message);
}
public ArgsException(ErrorCode errorCode) {
this.errorCode = errorCode;
}
public ArgsException(ErrorCode errorCode, String errorParameter) {
this.errorCode = errorCode;
this.errorParameter = errorParameter;
}
public ArgsException(ErrorCode errorCode,
char errorArgumentId, String errorParameter) {
this.errorCode = errorCode;
this.errorParameter = errorParameter;
this.errorArgumentId = errorArgumentId;
}
public char getErrorArgumentId() {
return errorArgumentId;
}
public void setErrorArgumentId(char errorArgumentId) {
this.errorArgumentId = errorArgumentId;
}
public String getErrorParameter() {
return errorParameter;
}
public void setErrorParameter(String errorParameter) {
this.errorParameter = errorParameter;
}
public ErrorCode getErrorCode() {
return errorCode;
}
public void setErrorCode(ErrorCode errorCode) {
this.errorCode = errorCode;
}
public String errorMessage() {
switch (errorCode) {
case OK:
return "TILT: Should not get here.";
case UNEXPECTED_ARGUMENT:
return String.format("Argument -%c unexpected.", errorArgumentId);
case MISSING_STRING:
return String.format("Could not find string parameter for -%c.",
errorArgumentId);
case INVALID_INTEGER:
return String.format("Argument -%c expects an integer but was '%s'.",
errorArgumentId, errorParameter);
case MISSING_INTEGER:
return String.format("Could not find integer parameter for -%c.",
errorArgumentId);
case INVALID_DOUBLE:
return String.format("Argument -%c expects a double but was '%s'.",
errorArgumentId, errorParameter);
case MISSING_DOUBLE:
return String.format("Could not find double parameter for -%c.",
errorArgumentId);
case INVALID_ARGUMENT_NAME:
return String.format("'%c' is not a valid argument name.",
errorArgumentId);
case INVALID_ARGUMENT_FORMAT:
return String.format("'%s' is not a valid argument format.",
errorParameter);
}
return "";
}
public enum ErrorCode {
OK, INVALID_ARGUMENT_FORMAT, UNEXPECTED_ARGUMENT, INVALID_ARGUMENT_NAME,
MISSING_STRING,
MISSING_INTEGER, INVALID_INTEGER,
MISSING_DOUBLE, INVALID_DOUBLE
}
}
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It’s remarkable how much code is required to flesh out the details of this simple concept. One of the reasons for this is that we are using a particularly wordy language. Java, being a statically typed language, requires a lot of words in order to satisfy the type system. In a language like Ruby, Python, or Smalltalk, this program is much smaller.1
为了充实这么一个简单概念的细节，需要如此多代码，这很值得注意。原因之一是我们使用了 Java 这种唠叨型语言。作为一种静态类型语言，需要大量语句才能满足类型系统的要求。在 Ruby、Python 或 Smalltalk 等语言中，程序会短很多[1]。
Please read the code over one more time. Pay special attention to the way things are named, the size of the functions, and the formatting of the code. If you are an experienced programmer, you may have some quibbles here and there with various parts of the style or structure. Overall, however, I hope you conclude that this program is nicely written and has a clean structure.
请再次阅读这段代码。特别留意命名方式、函数大小和代码格式。如果你是经验丰富的程序员，可能会对风格或结构有着这样或那样的不同观点。不过，希望你认为这段程序总体上编写良好，有着整洁的结构。
For example, it should be obvious how you would add a new argument type, such as a date argument or a complex number argument, and that such an addition would require a trivial amount of effort. In short, it would simply require a new derivative of Argument-Marshaler, a new getXXX function, and a new case statement in the parseSchemaElement function. There would also probably be a new ArgsException.ErrorCode and a new error message.
例如，如何增加新参数类型，如日期或复杂数字参数。其实现手段很清楚，而且只需要花一点点力气即可。简言之，只需要从 ArgumentMarshaler 派生一个新类，写一个新的 getXXX 函数，在 parseSchemaElement 函数中添加一个新的 case 语句。可能还需要添加新的 ArgsException.Errorcode 和新错误信息。
How Did I Do This?
我怎么做的？
Let me set your mind at rest. I did not simply write this program from beginning to end in its current form. More importantly, I am not expecting you to be able to write clean and elegant programs in one pass. If we have learned anything over the last couple of decades, it is that programming is a craft more than it is a science. To write clean code, you must first write dirty code and then clean it.
先放松一下神经。这段程序并非从一开始就写成现在的样子。更重要的是，我也没指望你能够一次过写出整洁、漂亮的程序。如果说我们从过去几十年里面学到什么东西的话，那就是编程是一种技艺甚于科学的东西。要编写整洁代码，必须先写肮脏代码，然后再清理它。
This should not be a surprise to you. We learned this truth in grade school when our teachers tried (usually in vain) to get us to write rough drafts of our compositions. The process, they told us, was that we should write a rough draft, then a second draft, then several subsequent drafts until we had our final version. Writing clean compositions, they tried to tell us, is a matter of successive refinement.
你应该不会对此感到惊讶。我们在小学就学过这条真理了。那时，老师（通常是徒劳地）努力让我们写作文草稿。他们告诉我们，我们应该先写草稿，再写二稿，一次又一次地草撰，直至写出终稿。他们尽力告诉我们，写出好作文是一个逐步改进的过程。
Most freshman programmers (like most grade-schoolers) don’t follow this advice particularly well. They believe that the primary goal is to get the program working. Once it’s “working,” they move on to the next task, leaving the “working” program in whatever state they finally got it to “work.” Most seasoned programmers know that this is professional suicide.
多数新手程序员（就像多数小学生一样）没有特别认真地遵循这个建议。他们相信，首要任务是写出能工作的程序。只要程序“能工作”，就转移到下一个任务上，而那个“能工作”的程序就留在了最后那个所谓“能工作”的状态。多数老手程序员都知道，这是一种自毁行为。
# 4.2 ARGS: THE ROUGH DRAFT Args：草稿
Listing 14-8 shows an earlier version of the Args class. It “works.” And it’s messy.
代码清单 14-8 展示了 Args 类的一个早期版本。它“能工作”，但却很烂。
Listing 14-8 Args.java (first draft)
代码清单 14-8 Args.java（初稿）
import java.text.ParseException;
import java.util.*;
public class Args {
private String schema;
private String[] args;
private boolean valid = true;
private Set<Character> unexpectedArguments = new TreeSet<Character>();
private Map<Character, Boolean> booleanArgs =
new HashMap
<Character, Boolean>();
private Map<Character, String> stringArgs = new HashMap
<Character, String>();
private Map<Character, Integer> intArgs = new HashMap<Character, Integer>();
private Set<Character> argsFound = new HashSet<Character>();
private int currentArgument;
private char errorArgumentId = '\0';
private String errorParameter = "TILT";
private ErrorCode errorCode = ErrorCode.OK;
private enum ErrorCode {
OK, MISSING_STRING, MISSING_INTEGER, INVALID_INTEGER, UNEXPECTED_ARGUMENT
}
public Args(String schema, String[] args) throws ParseException {
this.schema = schema;
this.args = args;
valid = parse();
}
private boolean parse() throws ParseException {
if (schema.length() == 0 && args.length == 0)
return true;
parseSchema();
try {
parseArguments();
} catch (ArgsException e) {
}
return valid;
}
private boolean parseSchema() throws ParseException {
for (String element : schema.split(",")) {
if (element.length() > 0) {
String trimmedElement = element.trim();
parseSchemaElement(trimmedElement);
}
}
return true;
}
private void parseSchemaElement(String element) throws ParseException {
char elementId = element.charAt(0);
String elementTail = element.substring(1);
validateSchemaElementId(elementId);
if (isBooleanSchemaElement(elementTail))
parseBooleanSchemaElement(elementId);
else if (isStringSchemaElement(elementTail))
parseStringSchemaElement(elementId);
else if (isIntegerSchemaElement(elementTail)) {
parseIntegerSchemaElement(elementId);
} else {
throw new ParseException(
String.format("Argument: %c has invalid format: %s.",
elementId, elementTail), 0);
}
}
private void validateSchemaElementId(char elementId) throws ParseException {
if (!Character.isLetter(elementId)) {
throw new ParseException(
"Bad character:" + elementId + "in Args format: " + schema, 0);
}
}
private void parseBooleanSchemaElement(char elementId) {
booleanArgs.put(elementId, false);
}
private void parseIntegerSchemaElement(char elementId) {
intArgs.put(elementId, 0);
}
private void parseStringSchemaElement(char elementId) {
stringArgs.put(elementId, "");
}
private boolean isStringSchemaElement(String elementTail) {
return elementTail.equals("*");
}
private boolean isBooleanSchemaElement(String elementTail) {
return elementTail.length() == 0;
}
private boolean isIntegerSchemaElement(String elementTail) {
return elementTail.equals("#");
}
private boolean parseArguments() throws ArgsException {
for (currentArgument = 0; currentArgument < args.length; currentArgument++) {
String arg = args[currentArgument];
parseArgument(arg);
}
return true;
}
private void parseArgument(String arg) throws ArgsException {
if (arg.startsWith("-"))
parseElements(arg);
}
private void parseElements(String arg) throws ArgsException {
for (int i = 1; i < arg.length(); i++)
parseElement(arg.charAt(i));
}
private void parseElement(char argChar) throws ArgsException {
if (setArgument(argChar))
argsFound.add(argChar);
else {
unexpectedArguments.add(argChar);
errorCode = ErrorCode.UNEXPECTED_ARGUMENT;
valid = false;
}
}
private boolean setArgument(char argChar) throws ArgsException {
if (isBooleanArg(argChar))
setBooleanArg(argChar, true);
else if (isStringArg(argChar))
setStringArg(argChar);
else if (isIntArg(argChar))
setIntArg(argChar);
else
return false;
return true;
}
private boolean isIntArg(char argChar) {
return intArgs.containsKey(argChar);
}
private void setIntArg(char argChar) throws ArgsException {
currentArgument++;
String parameter = null;
try {
parameter = args[currentArgument];
intArgs.put(argChar, new Integer(parameter));
} catch (ArrayIndexOutOfBoundsException e) {
valid = false;
errorArgumentId = argChar;
errorCode = ErrorCode.MISSING_INTEGER;
throw new ArgsException();
} catch (NumberFormatException e) {
valid = false;
errorArgumentId = argChar;
errorParameter = parameter;
errorCode = ErrorCode.INVALID_INTEGER;
throw new ArgsException();
}
}
private void setStringArg(char argChar) throws ArgsException {
currentArgument++;
try {
stringArgs.put(argChar, args[currentArgument]);
} catch (ArrayIndexOutOfBoundsException e) {
valid = false;
errorArgumentId = argChar;
errorCode = ErrorCode.MISSING_STRING;
throw new ArgsException();
}
}
private boolean isStringArg(char argChar) {
return stringArgs.containsKey(argChar);
}
private void setBooleanArg(char argChar, boolean value) {
booleanArgs.put(argChar, value);
}
private boolean isBooleanArg(char argChar) {
return booleanArgs.containsKey(argChar);
}
public int cardinality() {
return argsFound.size();
}
public String usage() {
if (schema.length() > 0)
return "-[" + schema + "]";
else
return "";
}
public String errorMessage() throws Exception {
switch (errorCode) {
case OK:
throw new Exception("TILT: Should not get here.");
case UNEXPECTED_ARGUMENT:
return unexpectedArgumentMessage();
case MISSING_STRING:
return String.format("Could not find string parameter for -%c.",
errorArgumentId);
case INVALID_INTEGER:
return String.format("Argument -%c expects an integer but was '%s'.",
errorArgumentId, errorParameter);
case MISSING_INTEGER:
return String.format("Could not find integer parameter for -%c.",
errorArgumentId);
}
return "";
}
private String unexpectedArgumentMessage() {
StringBuffer message = new StringBuffer("Argument(s) -");
for (char c : unexpectedArguments) {
message.append(c);
}
message.append(" unexpected.");
return message.toString();
}
private boolean falseIfNull(Boolean b) {
return b != null && b;
}
private int zeroIfNull(Integer i) {
return i == null ? 0 : i;
}
private String blankIfNull(String s) {
return s == null ? "" : s;
}
public String getString(char arg) {
return blankIfNull(stringArgs.get(arg));
}
public int getInt(char arg) {
return zeroIfNull(intArgs.get(arg));
}
public boolean getBoolean(char arg) {
return falseIfNull(booleanArgs.get(arg));
}
public boolean has(char arg) {
return argsFound.contains(arg);
}
public boolean isValid() {
return valid;
}
private class ArgsException extends Exception {
}
}
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I hope your initial reaction to this mass of code is “I’m certainly glad he didn’t leave it like that!” If you feel like this, then remember that’s how other people are going to feel about code that you leave in rough-draft form.
希望你看到这段乱七八糟的代码时，第一反应是“他没就此罢手，真令人高兴！”如果你这么想，不如想想其他人对你留置在草稿形态的代码的想法吧。
Actually “rough draft” is probably the kindest thing you can say about this code. It’s clearly a work in progress. The sheer number of instance variables is daunting. The odd strings like “TILT,” the HashSets and TreeSets, and the try-catch-catch blocks all add up to a festering pile.
实际上，“草稿”大概会是你对这段代码的最高评价。它显然还需打磨。实体变量的数量多到吓人。诸如 TILT 之类奇怪的字符串，HashSet 和 TreeSets，还有那些 try-catch-catch 代码块，组成了一个烂摊子。
I had not wanted to write a festering pile. Indeed, I was trying to keep things reasonably well organized. You can probably tell that from my choice of function and variable names and the fact that there is a crude structure to the program. But, clearly, I had let the problem get away from me.
我不想写出一个烂摊子。我也一直想保持一切有序。从函数和变量命名，以及程序的粗略架构中，你可以看出这一点。不过，显然我没能做到。
The mess built gradually. Earlier versions had not been nearly so nasty. For example, Listing 14-9 shows an earlier version in which only Boolean arguments were working.
混乱是逐渐产生的。更早的版本并不如此肮脏。例如，代码清单 14-9 展示了一个早期版本代码，那时只支持 Boolean 参数。
Listing 14-9 Args.java (Boolean only)
代码清单 14-9 Args.java（只支持 Boolean）
package com.objectmentor.utilities.getopts;
import java.util.*;
public class Args {
private String schema;
private String[] args;
private boolean valid;
private Set<Character> unexpectedArguments = new TreeSet<Character>();
private Map<Character, Boolean> booleanArgs =
new HashMap<Character, Boolean>();
private int numberOfArguments = 0;
public Args(String schema, String[] args) {
this.schema = schema;
this.args = args;
valid = parse();
}
public boolean isValid() {
return valid;
}
private boolean parse() {
if (schema.length() == 0 && args.length == 0)
return true;
parseSchema();
parseArguments();
return unexpectedArguments.size() == 0;
}
private boolean parseSchema() {
for (String element : schema.split(",")) {
parseSchemaElement(element);
}
return true;
}
private void parseSchemaElement(String element) {
if (element.length() == 1) {
parseBooleanSchemaElement(element);
}
}
private void parseBooleanSchemaElement(String element) {
char c = element.charAt(0);
if (Character.isLetter(c)) {
booleanArgs.put(c, false);
}
}
private boolean parseArguments() {
for (String arg : args)
parseArgument(arg);
return true;
}
private void parseArgument(String arg) {
if (arg.startsWith("-"))
parseElements(arg);
}
private void parseElements(String arg) {
for (int i = 1; i < arg.length(); i++)
parseElement(arg.charAt(i));
}
private void parseElement(char argChar) {
if (isBoolean(argChar)) {
numberOfArguments++;
setBooleanArg(argChar, true);
} else
unexpectedArguments.add(argChar);
}
private void setBooleanArg(char argChar, boolean value) {
booleanArgs.put(argChar, value);
}
private boolean isBoolean(char argChar) {
return booleanArgs.containsKey(argChar);
}
public int cardinality() {
return numberOfArguments;
}
public String usage() {
if (schema.length() > 0)
return "-[" + schema + "]";
else
return "";
}
public String errorMessage() {
if (unexpectedArguments.size() > 0) {
return unexpectedArgumentMessage();
} else
return "";
}
private String unexpectedArgumentMessage() {
StringBuffer message = new StringBuffer("Argument(s) -");
for (char c : unexpectedArguments) {
message.append(c);
}
message.append(" unexpected.");
return message.toString();
}
public boolean getBoolean(char arg) {
return booleanArgs.get(arg);
}
}
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Although you can find plenty to complain about in this code, it’s really not that bad. It’s compact and simple and easy to understand. However, within this code it is easy to see the seeds of the later festering pile. It’s quite clear how this grew into the latter mess.
尽管你可能对这段代码很不满意，其实它并非如此之烂。它精练、简单，易于理解。然而，在这段代码中很容易找到后面烂摊子的根源。很清楚能看到小问题如何变成大混乱的。
Notice that the latter mess has only two more argument types than this: String and integer. The addition of just two more argument types had a massively negative impact on the code. It converted it from something that would have been reasonably maintainable into something that I would expect to become riddled with bugs and warts.
注意，后来的混乱代码只比这个版本多支持两种参数类型：String 和 integer。只增加两种参数类型支持，就对代码产生了如此巨大的负面影响。它从某种可维护之物变成了满是缺陷的东西。
I added the two argument types incrementally. First, I added the String argument, which yielded this:
我逐步添加了对这两种参数类型的支持。首先，我添加对 String 参数的支持，就像这样：
Listing 14-10 Args.java (Boolean and String)
代码清单 14-10 Args.java（Boolean 和 String）
package com.objectmentor.utilities.getopts;
import java.text.ParseException;
import java.util.*;
public class Args {
private String schema;
private String[] args;
private boolean valid = true;
private Set<Character> unexpectedArguments = new TreeSet<Character>();
private Map<Character, Boolean> booleanArgs =
new HashMap<Character, Boolean>();
private Map<Character, String> stringArgs =
new HashMap<Character, String>();
private Set<Character> argsFound = new HashSet<Character>();
private int currentArgument;
private char errorArgument = '\0';
enum ErrorCode {
OK, MISSING_STRING
}
private ErrorCode errorCode = ErrorCode.OK;
public Args(String schema, String[] args) throws ParseException {
this.schema = schema;
this.args = args;
valid = parse();
}
private boolean parse() throws ParseException {
if (schema.length() == 0 && args.length == 0)
return true;
parseSchema();
parseArguments();
return valid;
}
private boolean parseSchema() throws ParseException {
for (String element : schema.split(",")) {
if (element.length() > 0) {
String trimmedElement = element.trim();
parseSchemaElement(trimmedElement);
}
}
return true;
}
private void parseSchemaElement(String element) throws ParseException {
char elementId = element.charAt(0);
String elementTail = element.substring(1);
validateSchemaElementId(elementId);
if (isBooleanSchemaElement(elementTail))
parseBooleanSchemaElement(elementId);
else if (isStringSchemaElement(elementTail))
parseStringSchemaElement(elementId);
}
private void validateSchemaElementId(char elementId) throws ParseException {
if (!Character.isLetter(elementId)) {
throw new ParseException(
"Bad character:" + elementId + "in Args format: " + schema, 0);
}
}
private void parseStringSchemaElement(char elementId) {
stringArgs.put(elementId, " ");
}
private boolean isStringSchemaElement(String elementTail) {
return elementTail.equals("*");
}
private boolean isBooleanSchemaElement(String elementTail) {
return elementTail.length() == 0;
}
private void parseBooleanSchemaElement(char elementId) {
booleanArgs.put(elementId, false);
}
private boolean parseArguments() {
for (currentArgument = 0; currentArgument < args.length; currentArgument++) {
String arg = args[currentArgument];
parseArgument(arg);
}
return true;
}
private void parseArgument(String arg) {
if (arg.startsWith("-"))
parseElements(arg);
}
private void parseElements(String arg) {
for (int i = 1; i < arg.length(); i++)
parseElement(arg.charAt(i));
}
private void parseElement(char argChar) {
if (setArgument(argChar))
argsFound.add(argChar);
else {
unexpectedArguments.add(argChar);
valid = false;
}
}
private boolean setArgument(char argChar) {
boolean set = true;
if (isBoolean(argChar))
setBooleanArg(argChar, true);
else if (isString(argChar))
setStringArg(argChar, " ");
else
set = false;
return set;
}
private void setStringArg(char argChar, String s) {
currentArgument++;
try {
stringArgs.put(argChar, args[currentArgument]);
} catch (ArrayIndexOutOfBoundsException e) {
valid = false;
errorArgument = argChar;
errorCode = ErrorCode.MISSING_STRING;
}
}
private boolean isString(char argChar) {
return stringArgs.containsKey(argChar);
}
private void setBooleanArg(char argChar, boolean value) {
booleanArgs.put(argChar, value);
}
private boolean isBoolean(char argChar) {
return booleanArgs.containsKey(argChar);
}
public int cardinality() {
return argsFound.size();
}
public String usage() {
if (schema.length() > 0)
return "-[" + schema + "]";
else
return " ";
}
public String errorMessage() throws Exception {
if (unexpectedArguments.size() > 0) {
return unexpectedArgumentMessage();
} else
switch (errorCode) {
case MISSING_STRING:
return String.format("Could not find string parameter for -%c.", errorArgument);
case OK:
throw new Exception("TILT: Should not get here.");
}
return " ";
}
private String unexpectedArgumentMessage() {
StringBuffer message = new StringBuffer("Argument(s) -");
for (char c : unexpectedArguments) {
message.append(c);
}
message.append(" unexpected.");
return message.toString();
}
public boolean getBoolean(char arg) {
return falseIfNull(booleanArgs.get(arg));
}
private boolean falseIfNull(Boolean b) {
return b == null ? false : b;
}
public String getString(char arg) {
return blankIfNull(stringArgs.get(arg));
}
private String blankIfNull(String s) {
return s == null ? " " : s;
}
public boolean has(char arg) {
return argsFound.contains(arg);
}
public boolean isValid() {
return valid;
}
}
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You can see that this is starting to get out of hand. It’s still not horrible, but the mess is certainly starting to grow. It’s a pile, but it’s not festering quite yet. It took the addition of the integer argument type to get this pile really fermenting and festering.
你可以看到，代码开始失去控制。还算不上可怕，但混乱已经开始生长。已经出现了一堆东西，不过还没烂掉。增加对整数参数类型的支持后，那堆东西就真的变质腐烂了。
# 14.2.1 So I Stopped 所以我暂停了
I had at least two more argument types to add, and I could tell that they would make things much worse. If I bulldozed my way forward, I could probably get them to work, but I’d leave behind a mess that was too large to fix. If the structure of this code was ever going to be maintainable, now was the time to fix it.
还有至少两种参数类型要添加，而且情形一定会更加糟糕。如果一味蛮干，大概也能让它工作，不过就会留下一大堆要调整的混乱。如果希望代码结构一直可维护，现在就是调整的时机了。
So I stopped adding features and started refactoring. Having just added the String and integer arguments, I knew that each argument type required new code in three major places. First, each argument type required some way to parse its schema element in order to select the HashMap for that type. Next, each argument type needed to be parsed in the command-line strings and converted to its true type. Finally, each argument type needed a getXXX method so that it could be returned to the caller as its true type.
所以我暂停添加特性，开始重构。由于刚添加了 String 和 integer 参数，我知道每种参数类型都需要在三个主要位置增加新代码。首先，每种参数类型都要有解析其范式元素、从而为该种类型选择 HashMap 的方法。其次，每种参数类型都需要在命令行字符串中解析，然后再转换为真实类型。最后，每种参数类型都需要一个 getXXX 方法，按照其真实类型向调用者返回参数值。
Many different types, all with similar methods—that sounds like a class to me. And so the ArgumentMarshaler concept was born.
许多种不同类型，类似的方法 ——听起来像是个类。ArgumentMarshaler 的概念就是这样产生的。
# 14.2.2 On Incrementalism 渐进
One of the best ways to ruin a program is to make massive changes to its structure in the name of improvement. Some programs never recover from such “improvements.” The problem is that it’s very hard to get the program working the same way it worked before the “improvement.”
毁坏程序的最好方法之一就是以改进之名大动其结构。有些程序永远不能从这种所谓“改进”中恢复过来。问题在于，很难让程序以“改进”之前的方式工作。
ARGS: THE ROUGH DRAFT To avoid this, I use the discipline of Test-Driven Development (TDD). One of the central doctrines of this approach is to keep the system running at all times. In other words, using TDD, I am not allowed to make a change to the system that breaks that system. Every change I make must keep the system working as it worked before.
为了避免这种状况发生，我采用了测试驱动开发的规程。这种手法的核心原则之一是保持系统始终能运行。换言之，采用 TDD，我不会允许做出破坏系统的修改。每次修改都必须保证系统能像以前一样工作。
To achieve this, I need a suite of automated tests that I can run on a whim and that verifies that the behavior of the system is unchanged. For the Args class I had created a suite of unit and acceptance tests while I was building the festering pile. The unit tests were written in Java and administered by JUnit. The acceptance tests were written as wiki pages in FitNesse. I could run these tests any time I wanted, and if they passed, I was confident that the system was working as I specified.
我需要一套能随需运行、确保系统行为不会改动的自动化测试。在我搞出那个烂摊子的同时，也为 Args 类创建了一套单元测试和验收测试。单元测试用 Java 写成，采用 JUnit 管理。验收测试用 FitNesse 以 wiki 页形式写成。我可以随时运行这些测试，如果测试通过，就能打包票说系统以我期望的方式工作。
So I proceeded to make a large number of very tiny changes. Each change moved the structure of the system toward the ArgumentMarshaler concept. And yet each change kept the system working. The first change I made was to add the skeleton of the ArgumentMarshaller to the end of the festering pile (Listing 14-11).
于是我开始做出大量小规模修改。每次修改都将系统结构向 ArgumentMarshaler 概念的方向推动。而且每次修改后，系统都要能工作。第一个修改是在烂摊子末尾添加 ArgumentMarshaler 的轮廓。
Listing 14-11 ArgumentMarshaller appended to Args.java
代码清单 14-11 向 Args.java 添加 ArgumentMarshaler
private class ArgumentMarshaler {
private boolean booleanValue = false;
public void setBoolean(boolean value) {
booleanValue = value;
}
public boolean getBoolean() {
return booleanValue;
}
}
private class BooleanArgumentMarshaler extends ArgumentMarshaler {
}
private class StringArgumentMarshaler extends ArgumentMarshaler {
}
private class IntegerArgumentMarshaler extends ArgumentMarshaler {
}
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Clearly, this wasn’t going to break anything. So then I made the simplest modification I could, one that would break as little as possible. I changed the HashMap for the Boolean arguments to take an ArgumentMarshaler.
显然，这什么也不会破坏。于是我做了一点最简单的、破坏性尽可能小的修改。我修改了 HashMap，采用 ArgumentMarshaler，使之支持 Boolean 参数。
private Map<Character, ArgumentMarshaler> booleanArgs = new HashMap<Character, ArgumentMarshaler>();
This broke a few statements, which I quickly fixed.
这个修改影响到少数语句，我很快就修正了。
…
private void parseBooleanSchemaElement(char elementId) {
booleanArgs.put(elementId, new BooleanArgumentMarshaler());
}
…
private void setBooleanArg(char argChar, boolean value) {
booleanArgs.get(argChar).setBoolean(value);
}
…
public boolean getBoolean(char arg) {
return falseIfNull(booleanArgs.get(arg).getBoolean());
}
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Notice how these changes are in exactly the areas that I mentioned before: the parse, set, and get for the argument type. Unfortunately, small as this change was, some of the tests started failing. If you look carefully at getBoolean, you’ll see that if you call it with 'y,' but there is no y argument, then booleanArgs.get('y') will return null, and the function will throw a NullPointerException. The falseIfNull function had been used to protect against this, but the change I made caused that function to become irrelevant.
注意，这些修改正是在我之前提到的那些区域之内所做的：参数类型的 parse、set 和 get 操作。不幸的是，即便修改如此细微，有些测试还是会失败。仔细看 getBoolean，可以看到如果用 y 去调用、而并没有 y 这个参数，则 booleanArgs.get('y')就会返回 null 值，函数将抛出一个 NullPointerException 异常。函数 falseIfNull 用以防止这种状况发生，但我做出的修改却导致该函数无所作为。
Incrementalism demanded that I get this working quickly before making any other changes. Indeed, the fix was not too difficult. I just had to move the check for null. It was no longer the boolean being null that I needed to check; it was the ArgumentMarshaller.
渐进主义要求我在做其他修改之前迅速修正这个问题。修正并不费劲。我只是把对 null 值的检查移了个位置。再也不用检测 bollean 是否为 null，而是检查 ArgumentMarshaler 是否为 null。
First, I removed the falseIfNull call in the getBoolean function. It was useless now, so I also eliminated the function itself. The tests still failed in the same way, so I was confident that I hadn’t introduced any new errors.
首先，我移除了 getBoolean 函数中的 falseIfNull 调用。现在它没什么用了，所以我也删去了这个函数。测试还是以同样的方式失败，所以我确定没有引入新的错误。
public boolean getBoolean(char arg) {
return booleanArgs.get(arg).getBoolean();
}
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Next, I split the function into two lines and put the ArgumentMarshaller into its own variable named argumentMarshaller. I didn’t care for the long variable name; it was badly redundant and cluttered up the function. So I shortened it to am [N5].
下一步，我把函数拆解为两行，并把 ArgumentMarshaler 放到它自己的名为 argumentMarshaler 的变量中[2]。我不在意变量名太长，但它却有点啰嗦，把函数搞得支离破碎。所以我把变量名缩短为 am[N5]。
public boolean getBoolean(char arg) {
Args.ArgumentMarshaler am = booleanArgs.get(arg);
return am.getBoolean();
}
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And then I put in the null detection logic.
然后再放入检测 null 值的逻辑。
public boolean getBoolean(char arg) {
Args.ArgumentMarshaler am = booleanArgs.get(arg);
return am != null && am.getBoolean();
}
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# 14.3 STRING ARGUMENTS 字符串参数
Addin_g String arguments was very similar to adding boolean arguments. I had to change the HashMap and get the parse, set, and get functions working. There shouldn’t be any surprises in what follows except, perhaps, that I seem to be putting all the marshalling implementation in the ArgumentMarshaller base class instead of distributing it to the derivatives.
添加 String 参数和添加 boolean 参数非常像。我要修改 HashMap，让 parse、set 和 get 函数能工作。跟着就是按部就班，但我似乎该把所有的 marshalling（编组）实现放到 ArgumentMarshaler 基类而不是派生类中。
private Map<Character, ArgumentMarshaler> stringArgs =
new HashMap<Character, ArgumentMarshaler>();
…
private void parseStringSchemaElement(char elementId) {
stringArgs.put(elementId, new StringArgumentMarshaler());
}
…
private void setStringArg(char argChar) throws ArgsException {
currentArgument++;
try {
stringArgs.get(argChar).setString(args[currentArgument]);
} catch (ArrayIndexOutOfBoundsException e) {
valid = false;
errorArgumentId = argChar;
errorCode = ErrorCode.MISSING_STRING;
throw new ArgsException();
}
}
…
public String getString(char arg) {
Args.ArgumentMarshaler am = stringArgs.get(arg);
return am == null ? “ ” : am.getString();
}
…
private class ArgumentMarshaler {
private boolean booleanValue = false;
private String stringValue;
public void setBoolean(boolean value) {
booleanValue = value;
}
public boolean getBoolean() {
return booleanValue;
}
public void setString(String s) {
stringValue = s;
}
public String getString() {
return stringValue == null ? “ ” : stringValue;
}
}
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Again, these changes were made one at a time and in such a way that the tests kept running, if not passing. When a test broke, I made sure to get it passing again before continuing with the next change.
同样，也是每次修改一个地方，持续运行测试。如果测试出错，在做下一个修改前确保通过。
By now you should be able to see my intent. Once I get all the current marshalling behavior into the ArgumentMarshaler base class, I’m going to start pushing that behavior down into the derivatives. This will allow me to keep everything running while I gradually change the shape of this program.
现在你应该明白我的意图了。一旦我将当前的编组行为放到 ArgumentMarshaler 基类中，就会开始往派生类推入该行为。这样，在我逐渐修改程序的形状时，还能保持一切正常。
The obvious next step was to move the int argument functionality into the ArgumentMarshaler. Again, there weren’t any surprises.
下一步显而易见，把 int 参数的相关功能放到 ArgumentMarshaler 里面。同样，也是照方抓药。
private Map<Character, ArgumentMarshaler> intArgs =
new HashMap<Character, ArgumentMarshaler>();
…
private void parseIntegerSchemaElement(char elementId) {
intArgs.put(elementId, new IntegerArgumentMarshaler());
}
…
private void setIntArg(char argChar) throws ArgsException {
currentArgument++;
String parameter = null;
try {
parameter = args[currentArgument];
intArgs.get(argChar).setInteger(Integer.parseInt(parameter));
} catch (ArrayIndexOutOfBoundsException e) {
valid = false;
errorArgumentId = argChar;
errorCode = ErrorCode.MISSING_INTEGER;
throw new ArgsException();
} catch (NumberFormatException e) {
valid = false;
errorArgumentId = argChar;
errorParameter = parameter;
errorCode = ErrorCode.INVALID_INTEGER;
throw new ArgsException();
}
}
…
public int getInt(char arg) {
Args.ArgumentMarshaler am = intArgs.get(arg);
return am == null ? 0 : am.getInteger();
}
…
private class ArgumentMarshaler {
private boolean booleanValue = false;
private String stringValue;
private int integerValue;
public void setBoolean(boolean value) {
booleanValue = value;
}
public boolean getBoolean() {
return booleanValue;
}
public void setString(String s) {
stringValue = s;
}
public String getString() {
return stringValue == null ? “ ”: stringValue;
}
public void setInteger(int i) {
integerValue = i;
}
public int getInteger() {
return integerValue;
}
}
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With all the marshalling moved to the ArgumentMarshaler, I started pushing functionality into the derivatives. The first step was to move the setBoolean function into the BooleanArgumentMarshaller and make sure it got called correctly. So I created an abstract set method.
当所有的编组操作都放到了 ArgumentMarshaler 中，我开始向派生类移植功能。第一步是把 setBoolean 函数放到 BooleanArgumentMarshaler 中，确保它能正确调用。所以我创建了一个抽象的 set 方法。
private abstract class ArgumentMarshaler {
protected boolean booleanValue = false;
private String stringValue;
private int integerValue;
public void setBoolean(boolean value) {
booleanValue = value;
}
public boolean getBoolean() {
return booleanValue;
}
public void setString(String s) {
stringValue = s;
}
public String getString() {
return stringValue == null ? " " : stringValue;
}
public void setInteger(int i) {
integerValue = i;
}
public int getInteger() {
return integerValue;
}
public abstract void set(String s);
}
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Then I implemented the set method in BooleanArgumentMarshaller.
然后在 BooleanArgumentMarshaler 中实现 set 方法。
private class BooleanArgumentMarshaler extends ArgumentMarshaler {
public void set(String s) {
booleanValue = true;
}
}
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And finally I replaced the call to setBoolean with a call to set.
最后，通过调用 set，替换对 setBoolean 的调用。
private void setBooleanArg(char argChar, boolean value) {
booleanArgs.get(argChar) .set(“true”);
}
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The tests all still passed. Because this change caused set to be deployed to the Boolean-ArgumentMarshaler, I removed the setBoolean method from the ArgumentMarshaler base class.
测试仍然全部通过。因为这次修改导致 set 函数放到了 BooleanArgumentMarshaler 里面，我就从 ArgumentMarshaler 基类删除了 setBoolean 方法。
Notice that the abstract set function takes a String argument, but the implementation in the BooleanArgumentMarshaller does not use it. I put that argument in there because I knew that the StringArgumentMarshaller and IntegerArgumentMarshaller would use it.
注意，抽象函数 set 有一个 String 参数，但其在 BooleanArgumentMarshaler 中的实现却没有使用这个参数。之所以在这里放个参数，是因为我知道 StringArgumentMarshaler 和 IntegerArgumentMarshaler 可能会使用它。
Next, I wanted to deploy the get method into BooleanArgumentMarshaler. Deploying get functions is always ugly because the return type has to be Object, and in this case needs to be cast to a Boolean.
跟着，我打算把 get 方法放到 BooleanArgumentMarshaler 中。这有点难看，因为返回类型必须是 Object，且在这里需要转换为 Boolean 值。
public boolean getBoolean(char arg) {
Args.ArgumentMarshaler am = booleanArgs.get(arg);
return am != null && (Boolean)am.get();
}
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Just to get this to compile, I added the get function to the ArgumentMarshaler.
为了编译通过，我把 get 函数加到 ArgumentMarshaler 中。
private abstract class ArgumentMarshaler {
…
public Object get() {
return null;
}
}
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This compiled and obviously failed the tests. Getting the tests working again was simply a matter of making get abstract and implementing it in BooleanAgumentMarshaler.
这样一来，虽然可以编译，但却无法通过测试。只要将 get 修改为抽象方法，并在 BooleanArgumentMarshaler 中实现，就能重新通过测试。
private abstract class ArgumentMarshaler {
protected boolean booleanValue = false;
…
public abstract Object get();
}
private class BooleanArgumentMarshaler extends ArgumentMarshaler {
public void set(String s) {
booleanValue = true;
}
public Object get() {
return booleanValue;
}
}
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Once again the tests passed. So both get and set deploy to the BooleanArgumentMarshaler! This allowed me to remove the old getBoolean function from ArgumentMarshaler, move the protected booleanValue variable down to BooleanArgumentMarshaler, and make it private.
测试又通过了。get 和 set 方法都已部署到 BooleanArgumentMarshaler 中！这样我就可以从 ArgumentMarshaler 里面移除旧的 getBoolean 函数，把受保护的 booleanValue 变量向下移动到 BooleanArgumentMarshaler，并将其设置为 private。
I did the same pattern of changes for Strings. I deployed both set and get, deleted the unused functions, and moved the variables.
对于 String 也照此办理。我修改了 set 和 get 的部署方式，删除无用的函数，并移动了变量。
private void setStringArg(char argChar) throws ArgsException {
currentArgument++;
try {
stringArgs.get(argChar).set(args[currentArgument]);
} catch (ArrayIndexOutOfBoundsException e) {
valid = false;
errorArgumentId = argChar;
errorCode = ErrorCode.MISSING_STRING;
throw new ArgsException();
}
}
…
public String getString(char arg) {
Args.ArgumentMarshaler am = stringArgs.get(arg);
return am == null ? " " : (String) am.get();
}
…
private abstract class ArgumentMarshaler {
private int integerValue;
public void setInteger(int i) {
integerValue = i;
}
public int getInteger() {
return integerValue;
}
public abstract void set(String s);
public abstract Object get();
}
private class BooleanArgumentMarshaler extends ArgumentMarshaler {
private boolean booleanValue = false;
public void set(String s) {
booleanValue = true;
}
public Object get() {
return booleanValue;
}
}
private class StringArgumentMarshaler extends ArgumentMarshaler {
private String stringValue = " ";
public void set(String s) {
stringValue = s;
}
public Object get() {
return stringValue;
}
}
private class IntegerArgumentMarshaler extends ArgumentMarshaler {
public void set(String s) {
}
public Object get() {
return null;
}
}
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Finally, I repeated the process for integers. This was just a little more complicated because integers needed to be parsed, and the parse operation can throw an exception. But the result is better because the whole concept of NumberFormatException got buried in the IntegerArgumentMarshaler.
最后，我为 integer 类型参数重复这个过程。这稍稍复杂一点，因为 integer 需要解析，而 parse 操作会抛出异常。不过结果会更好，因为 NumberFormatException 的概念在 IntegerArgumentMarshaler 中隐藏了。
private boolean isIntArg(char argChar) {return intArgs.containsKey(argChar);}
private void setIntArg(char argChar) throws ArgsException {
currentArgument++;
String parameter = null;
try {
parameter = args[currentArgument];
intArgs.get(argChar).set(parameter);
} catch (ArrayIndexOutOfBoundsException e) {
valid = false;
errorArgumentId = argChar;
errorCode = ErrorCode.MISSING_INTEGER;
throw new ArgsException();
} catch (ArgsException e) {
valid = false;
errorArgumentId = argChar;
errorParameter = parameter;
errorCode = ErrorCode.INVALID_INTEGER;
throw e;
}
}
…
private void setBooleanArg(char argChar) {
try {
booleanArgs.get(argChar).set(“true”);
} catch (ArgsException e) {
}
}
…
public int getInt(char arg) {
Args.ArgumentMarshaler am = intArgs.get(arg);
return am == null ? 0 : (Integer) am.get();
}
…
private abstract class ArgumentMarshaler {
public abstract void set(String s) throws ArgsException;
public abstract Object get();
}
…
private class IntegerArgumentMarshaler extends ArgumentMarshaler {
private int intValue = 0;
public void set(String s) throws ArgsException {
try {
intValue = Integer.parseInt(s);
} catch (NumberFormatException e) {
throw new ArgsException();
}
}
public Object get() {
return intValue;
}
}
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Of course, the tests continued to pass. Next, I got rid of the three different maps up at the top of the algorithm. This made the whole system much more generic. However, I couldn’t get rid of them just by deleting them because that would break the system. Instead, I added a new Map for the ArgumentMarshaler and then one by one changed the methods to use it instead of the three original maps.
测试当然继续通过。下一步，我要删掉算法顶端的三种不同 Map。这样，整个系统就变得更通用了。不过，只是删除它们却无法达到目的，因为那样会破坏系统。反之，我为 ArgumentMarshaler 添加一个新的 Map，然后再逐个修改那些方法，让方法调用这个新 Map。
public class Args {
…
private Map<Character, ArgumentMarshaler> booleanArgs =
new HashMap<Character, ArgumentMarshaler>();
private Map<Character, ArgumentMarshaler> stringArgs =
new HashMap<Character, ArgumentMarshaler>();
private Map<Character, ArgumentMarshaler> intArgs =
new HashMap<Character, ArgumentMarshaler>();
private Map<Character, ArgumentMarshaler> marshalers =
new HashMap<Character, ArgumentMarshaler>();
…
private void parseBooleanSchemaElement(char elementId) {
ArgumentMarshaler m = new BooleanArgumentMarshaler();
booleanArgs.put(elementId, m);
marshalers.put(elementId, m);
}
private void parseIntegerSchemaElement(char elementId) {
ArgumentMarshaler m = new IntegerArgumentMarshaler();
intArgs.put(elementId, m);
marshalers.put(elementId, m);
}
private void parseStringSchemaElement(char elementId) {
ArgumentMarshaler m = new StringArgumentMarshaler();
stringArgs.put(elementId, m);
marshalers.put(elementId, m);
}
}
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Of course the tests all still passed. Next, I changed isBooleanArg from this:
当然，测试还是通过了。接着，我把 isBooleanArg：
private boolean isBooleanArg(char argChar) {
return booleanArgs.containsKey(argChar);
}
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to this:
修改成这样：
private boolean isBooleanArg(char argChar) {
ArgumentMarshaler m = marshalers.get(argChar);
return m instanceof BooleanArgumentMarshaler;
}
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The tests still passed. So I made the same change to isIntArg and isStringArg.
测试仍然通过。于是我修改了一下 isIntArg 和 isStringArg。
private boolean isIntArg(char argChar) {
ArgumentMarshaler m = marshalers.get(argChar);
return m instanceof IntegerArgumentMarshaler;
}
private boolean isStringArg(char argChar) {
ArgumentMarshaler m = marshalers.get(argChar);
return m instanceof StringArgumentMarshaler;
}
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The tests still passed. So I eliminated all the duplicate calls to marshalers.get as follows:
测试继续通过。我跟着消除了对 marshaler.get 的重复调用：
private boolean setArgument(char argChar) throws ArgsException {
ArgumentMarshaler m = marshalers.get(argChar);
if (isBooleanArg(m))
setBooleanArg(argChar);
else if (isStringArg(m))
setStringArg(argChar);
else if (isIntArg(m))
setIntArg(argChar);
else
return false;
return true;
}
private boolean isIntArg(ArgumentMarshaler m) {
return m instanceof IntegerArgumentMarshaler;
}
private boolean isStringArg(ArgumentMarshaler m) {
return m instanceof StringArgumentMarshaler;
}
private boolean isBooleanArg(ArgumentMarshaler m) {
return m instanceof BooleanArgumentMarshaler;
}
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This left no good reason for the three isxxxArg methods. So I inlined them:
存在三个 isxxxArg 方法毫无道理。所以我做了内联修改：
private boolean setArgument(char argChar) throws ArgsException {
ArgumentMarshaler m = marshalers.get(argChar);
if (m instanceof BooleanArgumentMarshaler)
setBooleanArg(argChar);
else if (m instanceof StringArgumentMarshaler)
setStringArg(argChar);
else if (m instanceof IntegerArgumentMarshaler)
setIntArg(argChar);
else
return false;
return true;
}
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Next, I started using the marshalers map in the set functions, breaking the use of the other three maps. I started with the booleans.
下一步，我开始在 set 函数中使用 marshaler 映射，停止使用另外三个映射映射。从 boolean 开始：
public class Args {
private boolean setArgument(char argChar) throws ArgsException {
ArgumentMarshaler m = marshalers.get(argChar);
if (m instanceof BooleanArgumentMarshaler)
setBooleanArg(m);
else if (m instanceof StringArgumentMarshaler)
setStringArg(argChar);
else if (m instanceof IntegerArgumentMarshaler)
setIntArg(argChar);
else
return false;
return true;
}
…
private void setBooleanArg(ArgumentMarshaler m) {
try {
m.set("true"); // was: booleanArgs.get(argChar).set("true");
} catch (ArgsException e) {
}
}
}
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The tests still passed, so I did the same with Strings and Integers. This allowed me to integrate some of the ugly exception management code into the setArgument function.
测试通过，于是我如法炮制 String 和 Integer 参数。这样我就能把有些丑陋的异常管理代码整合到 setArgument 函数中。
private boolean setArgument(char argChar) throws ArgsException {
ArgumentMarshaler m = marshalers.get(argChar);
try {
if (m instanceof BooleanArgumentMarshaler)
setBooleanArg(m);
else if (m instanceof StringArgumentMarshaler)
setStringArg(m);
else if (m instanceof IntegerArgumentMarshaler)
setIntArg(m);
else
return false;
} catch (ArgsException e) {
valid = false;
errorArgumentId = argChar;
throw e;
}
return true;
}
private void setIntArg(ArgumentMarshaler m) throws ArgsException {
currentArgument++;
String parameter = null;
try {
parameter = args[currentArgument];
m.set(parameter);
} catch (ArrayIndexOutOfBoundsException e) {
errorCode = ErrorCode.MISSING_INTEGER;
throw new ArgsException();
} catch (ArgsException e) {
errorParameter = parameter;
errorCode = ErrorCode.INVALID_INTEGER;
throw e;
}
}
private void setStringArg(ArgumentMarshaler m) throws ArgsException {
currentArgument++;
try {
m.set(args[currentArgument]);
} catch (ArrayIndexOutOfBoundsException e) {
errorCode = ErrorCode.MISSING_STRING;
throw new ArgsException();
}
}
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I was close to being able to remove the three old maps. First, I needed to change the getBoolean function from this:
离彻底删除那 3 个旧映射的时机越来越近了。首先，我需要修改 getBoolean 函数：
public boolean getBoolean(char arg) {
Args.ArgumentMarshaler am = booleanArgs.get(arg);
return am != null && (Boolean) am.get();
}
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to this:
修改成这样：
public boolean getBoolean(char arg) {
Args.ArgumentMarshaler am = marshalers.get(arg);
boolean b = false;
try {
b = am != null && (Boolean) am.get();
} catch (ClassCastException e) {
b = false;
}
return b;
}
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This last change might have been a surprise. Why did I suddenly decide to deal with the ClassCastException? The reason is that I have a set of unit tests and a separate set of acceptance tests written in FitNesse. It turns out that the FitNesse tests made sure that if you called getBoolean on a nonboolean argument, you got a false. The unit tests did not. Up to this point I had only been running the unit tests.2
最后这个修改可能令人吃惊。为什么我会突然决定对付 ClassCastException？原因是我有一组单元测试，还有用 FitNesse 编写的一组验收测试。FitNesse 测试确认，如果用非布尔值参数调用 getBoolean，应该返回 false。可单元测试的结果不是这样。而到此时为止，我一直只调用单元测试[3]。
This last change allowed me to pull out another use of the boolean map:
这次修改把另一个对 boolean 映射的使用抽离了：
private void parseBooleanSchemaElement(char elementId) {
ArgumentMarshaler m = new BooleanArgumentMarshaler();
booleanArgs.put(elementId, m);
marshalers.put(elementId, m);
}
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And now we can delete the boolean map.
如此我们就能删除 boolean 映射。
public class Args {
…
private Map<Character, ArgumentMarshaler> booleanArgs
= new HashMap<Character, ArgumentMarshaler>();
private Map<Character, ArgumentMarshaler> stringArgs =
new HashMap<Character, ArgumentMarshaler>();
private Map<Character, ArgumentMarshaler> intArgs =
new HashMap<Character, ArgumentMarshaler>();
private Map<Character, ArgumentMarshaler> marshalers =
new HashMap<Character, ArgumentMarshaler>();
…
}
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Next, I migrated the String and Integer arguments in the same manner and did a little cleanup with the booleans.
接下来，我用同样的手法处理 String 和 Integer 参数，对 boolean 参数做了一点清理工作。
private void parseBooleanSchemaElement(char elementId) {
marshalers.put(elementId, new BooleanArgumentMarshaler());
}
private void parseIntegerSchemaElement(char elementId) {
marshalers.put(elementId, new IntegerArgumentMarshaler());
}
private void parseStringSchemaElement(char elementId) {
marshalers.put(elementId, new StringArgumentMarshaler());
}
…
public String getString(char arg) {
Args.ArgumentMarshaler am = marshalers.get(arg);
try {
return am == null ? “ ” : (String) am.get();
} catch (ClassCastException e) {
return “ ”;
}
}
public int getInt(char arg) {
Args.ArgumentMarshaler am = marshalers.get(arg);
try {
return am == null ? 0 : (Integer) am.get();
} catch (Exception e) {
return 0;
}
}
…
public class Args {
…
private Map<Character, ArgumentMarshaler> stringArgs =
new HashMap<Character, ArgumentMarshaler>();
private Map<Character, ArgumentMarshaler> intArgs =
new HashMap<Character, ArgumentMarshaler>();
private Map<Character, ArgumentMarshaler> marshalers =
new HashMap<Character, ArgumentMarshaler>();
…
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Next, I inlined the three parse methods because they didn’t do much anymore:
接着，由于那些 parse 方法没有太多事可做，我对它们进行了内联修改：
private void parseSchemaElement(String element) throws ParseException {
char elementId = element.charAt(0);
String elementTail = element.substring(1);
validateSchemaElementId(elementId);
if (isBooleanSchemaElement(elementTail))
marshalers.put(elementId, new BooleanArgumentMarshaler());
else if (isStringSchemaElement(elementTail))
marshalers.put(elementId, new StringArgumentMarshaler());
else if (isIntegerSchemaElement(elementTail)) {
marshalers.put(elementId, new IntegerArgumentMarshaler());
} else {
throw new ParseException(String.format(
"Argument: %c has invalid format: %s.", elementId, elementTail), 0);
}
}
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Okay, so now let’s look at the whole picture again. Listing 14-12 shows the current form of the Args class.
行了，下面来看看全景吧。代码清单 14-12 展示了 Args 类的现状。
Listing 14-12 Args.java (After first refactoring)
代码清单 14-12 Args.java（首次重构后）
package com.objectmentor.utilities.getopts;
import java.text.ParseException;
import java.util.*;
public class Args {
private String schema;
private String[] args;
private boolean valid = true;
private Set<Character> unexpectedArguments = new TreeSet<Character>();
private Map<Character, ArgumentMarshaler> marshalers =
new HashMap<Character, ArgumentMarshaler>();
private Set<Character> argsFound = new HashSet<Character>();
private int currentArgument;
private char errorArgumentId = '\0';
private String errorParameter = "TILT";
private ErrorCode errorCode = ErrorCode.OK;
private enum ErrorCode {
OK, MISSING_STRING, MISSING_INTEGER, INVALID_INTEGER,
UNEXPECTED_ARGUMENT
}
public Args(String schema, String[] args) throws ParseException {
this.schema = schema;
this.args = args;
valid = parse();
}
private boolean parse() throws ParseException {
if (schema.length() == 0 && args.length == 0)
return true;
parseSchema();
try {
parseArguments();
} catch (ArgsException e) {
}
return valid;
}
private boolean parseSchema() throws ParseException {
for (String element : schema.split(",")) {
if (element.length() > 0) {
String trimmedElement = element.trim();
parseSchemaElement(trimmedElement);
}
}
return true;
}
private void parseSchemaElement(String element) throws ParseException {
char elementId = element.charAt(0);
String elementTail = element.substring(1);
validateSchemaElementId(elementId);
if (isBooleanSchemaElement(elementTail))
marshalers.put(elementId, new BooleanArgumentMarshaler());
else if (isStringSchemaElement(elementTail))
marshalers.put(elementId, new StringArgumentMarshaler());
else if (isIntegerSchemaElement(elementTail)) {
marshalers.put(elementId, new IntegerArgumentMarshaler());
} else {
throw new ParseException(String.format(
"Argument: %c has invalid format: %s.", elementId, elementTail), 0);
}
}
private void validateSchemaElementId(char elementId) throws ParseException {
if (!Character.isLetter(elementId)) {
throw new ParseException(
"Bad character:" + elementId + "in Args format: " + schema, 0);
}
}
private boolean isStringSchemaElement(String elementTail) {
return elementTail.equals("*");
}
private boolean isBooleanSchemaElement(String elementTail) {
return elementTail.length() == 0;
}
private boolean isIntegerSchemaElement(String elementTail) {
return elementTail.equals("-");
}
private boolean parseArguments() throws ArgsException {
for (currentArgument = 0; currentArgument < args.length; currentArgument++) {
String arg = args[currentArgument];
parseArgument(arg);
}
return true;
}
private void parseArgument(String arg) throws ArgsException {
if (arg.startsWith("-"))
parseElements(arg);
}
private void parseElements(String arg) throws ArgsException {
for (int i = 1; i < arg.length(); i++)
parseElement(arg.charAt(i));
}
private void parseElement(char argChar) throws ArgsException {
if (setArgument(argChar))
argsFound.add(argChar);
else {
unexpectedArguments.add(argChar);
errorCode = ErrorCode.UNEXPECTED_ARGUMENT;
valid = false;
}
}
private boolean setArgument(char argChar) throws ArgsException {
ArgumentMarshaler m = marshalers.get(argChar);
try {
if (m instanceof BooleanArgumentMarshaler)
setBooleanArg(m);
else if (m instanceof StringArgumentMarshaler)
setStringArg(m);
else if (m instanceof IntegerArgumentMarshaler)
setIntArg(m);
else
return false;
} catch (ArgsException e) {
valid = false;
errorArgumentId = argChar;
throw e;
}
return true;
}
private void setIntArg(ArgumentMarshaler m) throws ArgsException {
currentArgument++;
String parameter = null;
try {
parameter = args[currentArgument];
m.set(parameter);
} catch (ArrayIndexOutOfBoundsException e) {
errorCode = ErrorCode.MISSING_INTEGER;
throw new ArgsException();
} catch (ArgsException e) {
errorParameter = parameter;
errorCode = ErrorCode.INVALID_INTEGER;
throw e;
}
}
private void setStringArg(ArgumentMarshaler m) throws ArgsException {
currentArgument++;
try {
m.set(args[currentArgument]);
} catch (ArrayIndexOutOfBoundsException e) {
errorCode = ErrorCode.MISSING_STRING;
throw new ArgsException();
}
}
private void setBooleanArg(ArgumentMarshaler m) {
try {
m.set("true");
} catch (ArgsException e) {
}
}
public int cardinality() {
return argsFound.size();
}
public String usage() {
if (schema.length() > 0)
return "-[" + schema + "]";
else
return " ";
}
public String errorMessage() throws Exception {
switch (errorCode) {
case OK:
throw new Exception("TILT: Should not get here.");
case UNEXPECTED_ARGUMENT:
return unexpectedArgumentMessage();
case MISSING_STRING:
return String.format("Could not find string parameter for -%c.",
errorArgumentId);
case INVALID_INTEGER:
return String.format("Argument -%c expects an integer but was '%s'.",
errorArgumentId, errorParameter);
case MISSING_INTEGER:
return String.format("Could not find integer parameter for -%c.",
errorArgumentId);
}
return " ";
}
private String unexpectedArgumentMessage() {
StringBuffer message = new StringBuffer("Argument(s) -");
for (char c : unexpectedArguments) {
message.append(c);
}
message.append(" unexpected.");
return message.toString();
}
public boolean getBoolean(char arg) {
Args.ArgumentMarshaler am = marshalers.get(arg);
boolean b = false;
try {
b = am != null && (Boolean) am.get();
} catch (ClassCastException e) {
b = false;
}
return b;
}
public String getString(char arg) {
Args.ArgumentMarshaler am = marshalers.get(arg);
try {
return am == null ? " " : (String) am.get();
} catch (ClassCastException e) {
return " ";
}
}
public int getInt(char arg) {
Args.ArgumentMarshaler am = marshalers.get(arg);
try {
return am == null ? 0 : (Integer) am.get();
} catch (Exception e) {
return 0;
}
}
public boolean has(char arg) {
return argsFound.contains(arg);
}
public boolean isValid() {
return valid;
}
private class ArgsException extends Exception {
}
private abstract class ArgumentMarshaler {
public abstract void set(String s) throws ArgsException;
public abstract Object get();
}
private class BooleanArgumentMarshaler extends ArgumentMarshaler {
private boolean booleanValue = false;
public void set(String s) {
booleanValue = true;
}
public Object get() {
return booleanValue;
}
}
private class StringArgumentMarshaler extends ArgumentMarshaler {
private String stringValue = " ";
public void set(String s) {
stringValue = s;
}
public Object get() {
return stringValue;
}
}
private class IntegerArgumentMarshaler extends ArgumentMarshaler {
private int intValue = 0;
public void set(String s) throws ArgsException {
try {
intValue = Integer.parseInt(s);
} catch (NumberFormatException e) {
throw new ArgsException();
}
}
public Object get() {
return intValue;
}
}
}
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After all that work, this is a bit disappointing. The structure is a bit better, but we still have all those variables up at the top; there’s still a horrible type-case in setArgument; and all those set functions are really ugly. Not to mention all the error processing. We still have a lot of work ahead of us.
功夫费尽，还是有点失望。程序结构好了一点，但在代码顶端还是有那一堆变量；在 setArgument 里面还是有那么恐怖的类型转换操作；而且那些 set 函数真的很丑陋。就别提那些错误处理操作了。前头要做的事还很多。
I’d really like to get rid of that type-case up in setArgument [G23]. What I’d like in setArgument is a single call to ArgumentMarshaler.set. This means I need to push setIntArg, setStringArg, and setBooleanArg down into the appropriate ArgumentMarshaler derivatives. But there is a problem.
我真是想删掉 setArgument 里面那些类型转换操作[G23]。我想要 setArgument 只简单地调用 ArgumentMarshaler.set。这意味着我需要将 setIntArg、setStringArg 和 setBooleanArg 推到合适的 ArgumentMarshaler 派生类里面。不过这有个问题。
If you look closely at setIntArg, you’ll notice that it uses two instance variables: args and currentArg. To move setIntArg down into BooleanArgumentMarshaler, I’ll have to pass both args and currentArgs as function arguments. That’s dirty [F1]. I’d rather pass one argument instead of two. Fortunately, there is a simple solution. We can convert the args array into a list and pass an Iterator down to the set functions. The following took me ten steps, passing all the tests after each. But I’ll just show you the result. You should be able to figure out what most of the tiny little steps were.
仔细看 setIntArg，你会发现，它使用了两个实体变量：args 和 currentArg。为了把 setIntArg 移到 BooleanARgumentMarshaler 里面，我得把这两个变量都作为函数参数传递过去。那种做法太烂了[F1]。我只想传递一个参数。幸运的是，有个简单的解决方法。可以把 args 数组转换为一个 list，并向 set 函数传递一个 Iterator。这花了我 10 步功夫，每次都通过了测试。不过我只向你展示结果。你应该能看出每个小修改步骤。
public class Args {
private String schema;
private String[] args;
private boolean valid = true;
private Set<Character> unexpectedArguments = new TreeSet<Character>();
private Map<Character, ArgumentMarshaler> marshalers =
new HashMap<Character, ArgumentMarshaler>();
private Set<Character> argsFound = new HashSet<Character>();
private Iterator<String> currentArgument;
private char errorArgumentId = '\0';
private String errorParameter = "TILT";
private ErrorCode errorCode = ErrorCode.OK;
private List<String> argsList;
private enum ErrorCode {
OK, MISSING_STRING, MISSING_INTEGER, INVALID_INTEGER,
UNEXPECTED_ARGUMENT
}
public Args(String schema, String[] args) throws ParseException {
this.schema = schema;
argsList = Arrays.asList(args);
valid = parse();
}
private boolean parse() throws ParseException {
if (schema.length() == 0 && argsList.size() == 0)
return true;
parseSchema();
try {
parseArguments();
} catch (ArgsException e) {
}
return valid;
}
}
---
private boolean parseArguments() throws ArgsException {
for (currentArgument = argsList.iterator(); currentArgument.hasNext(); ) {
String arg = currentArgument.next();
parseArgument(arg);
}
return true;
}
---
private void setIntArg(ArgumentMarshaler m) throws ArgsException {
String parameter = null;
try {
parameter = currentArgument.next();
m.set(parameter);
} catch (NoSuchElementException e) {
errorCode = ErrorCode.MISSING_INTEGER;
throw new ArgsException();
} catch (ArgsException e) {
errorParameter = parameter;
errorCode = ErrorCode.INVALID_INTEGER;
throw e;
}
}
private void setStringArg(ArgumentMarshaler m) throws ArgsException {
try {
m.set(currentArgument.next());
} catch (NoSuchElementException e) {
errorCode = ErrorCode.MISSING_STRING;
throw new ArgsException();
}
}
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These were simple changes that kept all the tests passing. Now we can start moving the set functions down into the appropriate derivatives. First, I need to make the following change in setArgument:
是这些简单的修改让测试保持通过。现在我们可以开始把 set 函数移植到合适的派生类中了。第一步，我要在 setArgument 中做以下修改：
private boolean setArgument(char argChar) throws ArgsException {
ArgumentMarshaler m = marshalers.get(argChar);
if (m == null)
return false;
try {
if (m instanceof BooleanArgumentMarshaler)
setBooleanArg(m);
else if (m instanceof StringArgumentMarshaler)
setStringArg(m);
else if (m instanceof IntegerArgumentMarshaler)
setIntArg(m);
else
return false;
} catch (ArgsException e) {
valid = false;
errorArgumentId = argChar;
throw e;
}
return true;
}
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This change is important because we want to completely eliminate the if-else chain. Therefore, we needed to get the error condition out of it.
这个修改很重要，因为我们想要彻底删除那条 if-else 链。所以，需要把错误条件抽离。
Now we can start to move the set functions. The setBooleanArg function is trivial, so we’ll prepare that one first. Our goal is to change the setBooleanArg function to simply forward to the BooleanArgumentMarshaler.
现在可以开始移动 set 函数了。setBooleanArg 函数很小，就从它开始。目标是让 setBooleanArg 函数只与 BooleanArgumentMarshaler 有关。
private boolean setArgument(char argChar) throws ArgsException {
ArgumentMarshaler m = marshalers.get(argChar);
if (m == null)
return false;
try {
if (m instanceof BooleanArgumentMarshaler)
setBooleanArg(m, currentArgument);
else if (m instanceof StringArgumentMarshaler)
setStringArg(m);
else if (m instanceof IntegerArgumentMarshaler)
setIntArg(m);
} catch (ArgsException e) {
valid = false;
errorArgumentId = argChar;
throw e;
}
return true;
}
---
private void setBooleanArg(ArgumentMarshaler m, Iterator<String> currentArgument)
throws ArgsException {
try {
m.set("true");
} catch (ArgsException e) {
}
}
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Didn’t we just put that exception processing in? Putting things in so you can take them out again is pretty common in refactoring. The smallness of the steps and the need to keep the tests running means that you move things around a lot. Refactoring is a lot like solving a Rubik’s cube. There are lots of little steps required to achieve a large goal. Each step enables the next.
我们不是刚把那个异常处理放进去吗？放进拿出是重构过程中常见的事。小步幅和保持测试通过，意味着你会不断移动各种东西。重构有点像是解魔方。需要经过许多小步骤，才能达到较大目标。每一步都是下一步的基础。
Why did we pass that iterator when setBooleanArg certainly doesn’t need it? Because setIntArg and setStringArg will! And because I want to deploy all three of these functions through an abstract method in ArgumentMarshaller, I need to pass it to setBooleanArg.
为什么要在 setBooleanArg 根本不需要的情况下向其传递 iterator 呢？因为 setIntArg 和 setStringArg 需要！还因为我打算通过 ArgumentMarshaler 中的抽象方法部署这三个函数，需要将其传递给 setBooleanArg。
So now setBooleanArg is useless. If there were a set function in ArgumentMarshaler, we could call it directly. So it’s time to make that function! The first step is to add the new abstract method to ArgumentMarshaler.
现在 setBooleanArg 没用了。如果 ArgumentMarshaler 中有个 set 函数，我们可以直接调用它。是时候打造那个函数了！第一步，在 ArgumentMarshaler 中添加抽象方法。
private abstract class ArgumentMarshaler {
public abstract void set(Iterator<String> currentArgument)
throws ArgsException;
public abstract void set(String s) throws ArgsException;
public abstract Object get();
}
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Of course this breaks all the derivatives. So let’s implement the new method in each.
当然，这会影响到所有派生类。所以，要逐个实现新方法。
private class BooleanArgumentMarshaler extends ArgumentMarshaler {
private boolean booleanValue = false;
public void set(Iterator<String> currentArgument) throws ArgsException {
booleanValue = true;
}
public void set(String s) {
booleanValue = true;
}
public Object get() {
return booleanValue;
}
}
private class StringArgumentMarshaler extends ArgumentMarshaler {
private String stringValue = "";
public void set(Iterator<String> currentArgument) throws ArgsException {
}
public void set(String s) {
stringValue = s;
}
public Object get() {
return stringValue;
}
}
private class IntegerArgumentMarshaler extends ArgumentMarshaler {
private int intValue = 0;
public void set(Iterator<String> currentArgument) throws ArgsException {
}
public void set(String s) throws ArgsException {
try {
intValue = Integer.parseInt(s);
} catch (NumberFormatException e) {
throw new ArgsException();
}
}
public Object get() {
return intValue;
}
}
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And now we can eliminate setBooleanArg!
现在可以删除 setBooleanArg 了！
private boolean setArgument(char argChar) throws ArgsException {
ArgumentMarshaler m = marshalers.get(argChar);
if (m == null)
return false;
try {
if (m instanceof BooleanArgumentMarshaler)
m.set(currentArgument);
else if (m instanceof StringArgumentMarshaler)
setStringArg(m);
else if (m instanceof IntegerArgumentMarshaler)
setIntArg(m);
} catch (ArgsException e) {
valid = false;
errorArgumentId = argChar;
throw e;
}
return true;
}
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The tests all pass, and the set function is deploying to BooleanArgumentMarshaler! Now we can do the same for Strings and Integers.
测试全都通过，而且 set 函数也部署到 BooleanArgumentMarshaler 里面了！现在就能对 String 和 Integer 参数的处理做同样的修改。
private boolean setArgument(char argChar) throws ArgsException {
ArgumentMarshaler m = marshalers.get(argChar);
if (m == null)
return false;
try {
if (m instanceof BooleanArgumentMarshaler)
m.set(currentArgument);
else if (m instanceof StringArgumentMarshaler)
m.set(currentArgument);
else if (m instanceof IntegerArgumentMarshaler)
m.set(currentArgument);
} catch (ArgsException e) {
valid = false;
errorArgumentId = argChar;
throw e;
}
return true;
}
---
private class StringArgumentMarshaler extends ArgumentMarshaler {
private String stringValue = "";
public void set(Iterator<String> currentArgument) throws ArgsException {
try {
stringValue = currentArgument.next();
} catch (NoSuchElementException e) {
errorCode = ErrorCode.MISSING_STRING;
throw new ArgsException();
}
}
public void set(String s) {
}
public Object get() {
return stringValue;
}
}
private class IntegerArgumentMarshaler extends ArgumentMarshaler {
private int intValue = 0;
public void set(Iterator<String> currentArgument) throws ArgsException {
String parameter = null;
try {
parameter = currentArgument.next();
set(parameter);
} catch (NoSuchElementException e) {
errorCode = ErrorCode.MISSING_INTEGER;
throw new ArgsException();
} catch (ArgsException e) {
errorParameter = parameter;
errorCode = ErrorCode.INVALID_INTEGER;
throw e;
}
}
public void set(String s) throws ArgsException {
try {
intValue = Integer.parseInt(s);
} catch (NumberFormatException e) {
throw new ArgsException();
}
}
public Object get() {
return intValue;
}
}
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And so the coup de grace: The type-case can be removed! Touche!
最后一击：可以移除类型转换了！看招！
private boolean setArgument(char argChar) throws ArgsException {
ArgumentMarshaler m = marshalers.get(argChar);
if (m == null)
return false;
try {
m.set(currentArgument);
return true;
} catch (ArgsException e) {
valid = false;
errorArgumentId = argChar;
throw e;
}
}
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Now we can get rid of some crufty functions in IntegerArgumentMarshaler and clean it up a bit.
现在可以删掉 IntegerArgumentMarshaler 中那些过时的函数，做一下清理了。
private class IntegerArgumentMarshaler extends ArgumentMarshaler {
private int intValue = 0
public void set(Iterator<String> currentArgument) throws ArgsException {
String parameter = null;
try {
parameter = currentArgument.next();
intValue = Integer.parseInt(parameter);
} catch (NoSuchElementException e) {
errorCode = ErrorCode.MISSING_INTEGER;
throw new ArgsException();
} catch (NumberFormatException e) {
errorParameter = parameter;
errorCode = ErrorCode.INVALID_INTEGER;
throw new ArgsException();
}
}
public Object get() {
return intValue;
}
}
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We can also turn ArgumentMarshaler into an interface.
还可以把 ArgumentMarshaler 修改为接口。
private interface ArgumentMarshaler {
void set(Iterator<String> currentArgument) throws ArgsException;
Object get();
}
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So now let’s see how easy it is to add a new argument type to our structure. It should require very few changes, and those changes should be isolated. First, we begin by adding a new test case to check that the double argument works correctly.
现在来看看往这个结构中添加新的参数类型有多容易。只需要做少量修改，而且修改是被隔离的。首先，增加一个新的测试用例，检测 double 参数是否正常工作。
public void testSimpleDoublePresent() throws Exception {
Args args = new Args("x##", new String[]{"-x", "42.3"});
assertTrue(args.isValid());
assertEquals(1, args.cardinality());
assertTrue(args.has('x'));
assertEquals(42.3, args.getDouble('x'), .001);
}
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Now we clean up the schema parsing code and add the ## detection for the double argument type.
然后清理范式解析代码，为 double 参数类型添加 ## 监测。
private void parseSchemaElement(String element) throws ParseException {
char elementId = element.charAt(0);
String elementTail = element.substring(1);
validateSchemaElementId(elementId);
if (elementTail.length() == 0)
marshalers.put(elementId, new BooleanArgumentMarshaler());
else if (elementTail.equals("*"))
marshalers.put(elementId, new StringArgumentMarshaler());
else if (elementTail.equals("#"))
marshalers.put(elementId, new IntegerArgumentMarshaler());
else if (elementTail.equals("##"))
marshalers.put(elementId, new DoubleArgumentMarshaler());
else
throw new ParseException(String.format(
"Argument: %c has invalid format: %s.", elementId, elementTail), 0);
}
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Next, we write the DoubleArgumentMarshaler class.
下一步，编写 DoubleArgumentMarshaler 类。
private class DoubleArgumentMarshaler implements ArgumentMarshaler {
private double doubleValue = 0;
public void set(Iterator<String> currentArgument) throws ArgsException {
String parameter = null;
try {
parameter = currentArgument.next();
doubleValue = Double.parseDouble(parameter);
} catch (NoSuchElementException e) {
errorCode = ErrorCode.MISSING_DOUBLE;
throw new ArgsException();
} catch (NumberFormatException e) {
errorParameter = parameter;
errorCode = ErrorCode.INVALID_DOUBLE;
throw new ArgsException();
}
}
public Object get() {
return doubleValue;
}
}
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This forces us to add a new ErrorCode.
然后就得添加一个新的 ErrorCode：
private enum ErrorCode {
OK, MISSING_STRING, MISSING_INTEGER, INVALID_INTEGER, UNEXPECTED_ARGUMENT,
MISSING_DOUBLE, INVALID_DOUBLE
}
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And we need a getDouble function.
还需要一个 getDouble 函数：
public double getDouble(char arg) {
Args.ArgumentMarshaler am = marshalers.get(arg);
try {
return am == null ? 0 : (Double) am.get();
} catch (Exception e) {
return 0.0;
}
}
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And all the tests pass! That was pretty painless. So now let’s make sure all the error processing works correctly. The next test case checks that an error is declared if an unparseable string is fed to a ## argument.
全部测试都通过了！完全无痛。再来确保全部错误处理代码正确工作。下一个测试用例用来检测在向 ## 参数传递一个不可解析的字符串时是否会返回错误。
public void testInvalidDouble() throws Exception {
Args args = new Args("x##", new String[]{"-x", "Forty two"});
assertFalse(args.isValid());
assertEquals(0, args.cardinality());
assertFalse(args.has('x'));
assertEquals(0, args.getInt('x'));
assertEquals("Argument -x expects a double but was ‘Forty two'.",
args.errorMessage());
}
---
public String errorMessage() throws Exception {
switch (errorCode) {
case OK:
throw new Exception("TILT: Should not get here.");
case UNEXPECTED_ARGUMENT:
return unexpectedArgumentMessage();
case MISSING_STRING:
return String.format("Could not find string parameter for -%c.",
errorArgumentId);
case INVALID_INTEGER:
return String.format("Argument -%c expects an integer but was ‘%s’.",
errorArgumentId, errorParameter);
case MISSING_INTEGER:
return String.format("Could not find integer parameter for -%c.",
errorArgumentId);
case INVALID_DOUBLE:
return String.format("Argument -%c expects a double but was ‘%s’.",
errorArgumentId, errorParameter);
case MISSING_DOUBLE:
return String.format("Could not find double parameter for -%c.",
errorArgumentId);
}
return "";
}
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And the tests pass. The next test makes sure we detect a missing double argument properly.
测试通过。下一个测试确保我们正确检测到遗漏的 double 参数。
public void testMissingDouble() throws Exception {
Args args = new Args("x##", new String[]{"-x"});
assertFalse(args.isValid());
assertEquals(0, args.cardinality());
assertFalse(args.has('x'));
assertEquals(0.0, args.getDouble('x'), 0.01);
assertEquals("Could not find double parameter for -x.",
args.errorMessage());
}
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This passes as expected. We wrote it simply for completeness.
测试如期通过。我们只是为了保持一切完整而编写这个测试。
The exception code is pretty ugly and doesn’t really belong in the Args class. We are also throwing out ParseException, which doesn’t really belong to us. So let’s merge all the exceptions into a single ArgsException class and move it into its own module.
异常代码很丑陋，不该在 Args 类中存在。我们也抛出 ParseException，但那并不真的属于我们自己。那就把所有异常都塞到 ArgsException 类中，并将其移到它自己的模块里面。
public class ArgsException extends Exception {
private char errorArgumentId = '\0';
private String errorParameter = "TILT";
private ErrorCode errorCode = ErrorCode.OK;
public ArgsException() {
}
public ArgsException(String message) {
super(message);
}
public enum ErrorCode {
OK, MISSING_STRING, MISSING_INTEGER,
INVALID_INTEGER, UNEXPECTED_ARGUMENT,
MISSING_DOUBLE, INVALID_DOUBLE
}
}
---
public class Args {
…
private char errorArgumentId = '\0';
private String errorParameter = "TILT";
private ArgsException.ErrorCode errorCode = ArgsException.ErrorCode.OK;
private List<String> argsList;
public Args(String schema, String[] args) throws ArgsException {
this.schema = schema;
argsList = Arrays.asList(args);
valid = parse();
}
private boolean parse() throws ArgsException {
if (schema.length() == 0 && argsList.size() == 0)
return true;
parseSchema();
try {
parseArguments();
} catch (ArgsException e) {
}
return valid;
}
private boolean parseSchema() throws ArgsException {
…
}
private void parseSchemaElement(String element) throws ArgsException {
…
else
throw new ArgsException(
String.format("Argument: %c has invalid format: %s.",
elementId, elementTail));
}
private void validateSchemaElementId(char elementId) throws ArgsException {
if (!Character.isLetter(elementId)) {
throw new ArgsException(
"Bad character:" + elementId + "in Args format: " + schema);
}
}
…
private void parseElement(char argChar) throws ArgsException {
if (setArgument(argChar))
argsFound.add(argChar);
else {
unexpectedArguments.add(argChar);
errorCode = ArgsException.ErrorCode.UNEXPECTED_ARGUMENT;
valid = false;
}
}
…
private class StringArgumentMarshaler implements ArgumentMarshaler {
private String stringValue = "";
public void set(Iterator<String> currentArgument) throws ArgsException {
try {
stringValue = currentArgument.next();
} catch (NoSuchElementException e) {
errorCode = ArgsException.ErrorCode.MISSING_STRING;
throw new ArgsException();
}
}
public Object get() {
return stringValue;
}
}
private class IntegerArgumentMarshaler implements ArgumentMarshaler {
private int intValue = 0;
public void set(Iterator<String> currentArgument) throws ArgsException {
String parameter = null;
try {
parameter = currentArgument.next();
intValue = Integer.parseInt(parameter);
} catch (NoSuchElementException e) {
errorCode = ArgsException.ErrorCode.MISSING_INTEGER;
throw new ArgsException();
} catch (NumberFormatException e) {
errorParameter = parameter;
errorCode = ArgsException.ErrorCode.INVALID_INTEGER;
throw new ArgsException();
}
}
public Object get() {
return intValue;
}
}
private class DoubleArgumentMarshaler implements ArgumentMarshaler {
private double doubleValue = 0;
public void set(Iterator<String> currentArgument) throws ArgsException {
String parameter = null;
try {
parameter = currentArgument.next();
doubleValue = Double.parseDouble(parameter);
} catch (NoSuchElementException e) {
errorCode = ArgsException.ErrorCode.MISSING_DOUBLE;
throw new ArgsException();
} catch (NumberFormatException e) {
errorParameter = parameter;
errorCode = ArgsException.ErrorCode.INVALID_DOUBLE;
throw new ArgsException();
}
}
public Object get() {
return doubleValue;
}
}
}
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This is nice. Now the only exception thrown by Args is ArgsException. Moving ArgsException into its own module means that we can move a lot of the miscellaneous error support code into that module and out of the Args module. It provides a natural and obvious place to put all that code and will really help us clean up the Args module going forward.
很好。现在，Args 抛出的唯一一个异常是 ArgsException。把 ArgsException 移到它自己的模块中，意味着我们能把大量杂七杂八的错误支持代码从 Args 模块转移到这个模块。
So now we have completely separated the exception and error code from the Args module. (See Listing 14-13 through Listing 14-16.) This was achieved through a series of about 30 tiny steps, keeping the tests passing between each step.
现在我们完全把异常和错误代码从 Args 模块中隔离出来了。（如代码清单 14-13 ～ 16 所示。）为达到这一目标，大概做了 30 次小修改，每次修改都保持测试通过。
Listing 14-13 ArgsTest.java
代码清单 14-13 ArgsTest.java
package com.objectmentor.utilities.args;
import junit.framework.TestCase;
public class ArgsTest extends TestCase {
public void testCreateWithNoSchemaOrArguments() throws Exception {
Args args = new Args("", new String[0]);
assertEquals(0, args.cardinality());
}
public void testWithNoSchemaButWithOneArgument() throws Exception {
try {
new Args("", new String[]{"-x"});
fail();
} catch (ArgsException e) {
assertEquals(ArgsException.ErrorCode.UNEXPECTED_ARGUMENT,
e.getErrorCode());
assertEquals('x', e.getErrorArgumentId());
}
}
public void testWithNoSchemaButWithMultipleArguments() throws Exception {
try {
new Args("", new String[]{"-x", "-y"});
fail();
} catch (ArgsException e) {
assertEquals(ArgsException.ErrorCode.UNEXPECTED_ARGUMENT,
e.getErrorCode());
assertEquals('x', e.getErrorArgumentId());
}
}
public void testNonLetterSchema() throws Exception {
try {
new Args("*", new String[]{});
fail("Args constructor should have thrown exception");
} catch (ArgsException e) {
assertEquals(ArgsException.ErrorCode.INVALID_ARGUMENT_NAME,
e.getErrorCode());
assertEquals('*', e.getErrorArgumentId());
}
}
public void testInvalidArgumentFormat() throws Exception {
try {
new Args("f~", new String[]{});
fail("Args constructor should have throws exception");
} catch (ArgsException e) {
assertEquals(ArgsException.ErrorCode.INVALID_FORMAT, e.getErrorCode());
assertEquals('f', e.getErrorArgumentId());
}
}
public void testSimpleBooleanPresent() throws Exception {
Args args = new Args("x", new String[]{"-x"});
assertEquals(1, args.cardinality());
assertEquals(true, args.getBoolean('x'));
}
public void testSimpleStringPresent() throws Exception {
Args args = new Args("x*", new String[]{"-x", "param"});
assertEquals(1, args.cardinality());
assertTrue(args.has('x'));
assertEquals("param", args.getString('x'));
}
public void testMissingStringArgument() throws Exception {
try {
new Args("x*", new String[]{"-x"});
fail();
} catch (ArgsException e) {
assertEquals(ArgsException.ErrorCode.MISSING_STRING, e.getErrorCode());
assertEquals('x', e.getErrorArgumentId());
}
}
public void testSpacesInFormat() throws Exception {
Args args = new Args("x, y", new String[]{"-xy"});
assertEquals(2, args.cardinality());
assertTrue(args.has('x'));
assertTrue(args.has('y'));
}
public void testSimpleIntPresent() throws Exception {
Args args = new Args("x#", new String[]{"-x", "42"});
assertEquals(1, args.cardinality());
assertTrue(args.has('x'));
assertEquals(42, args.getInt('x'));
}
public void testInvalidInteger() throws Exception {
try {
new Args("x#", new String[]{"-x", "Forty two"});
fail();
} catch (ArgsException e) {
assertEquals(ArgsException.ErrorCode.INVALID_INTEGER, e.getErrorCode());
assertEquals('x', e.getErrorArgumentId());
assertEquals("Forty two", e.getErrorParameter());
}
}
public void testMissingInteger() throws Exception {
try {
new Args("x#", new String[]{"-x"});
fail();
} catch (ArgsException e) {
assertEquals(ArgsException.ErrorCode.MISSING_INTEGER, e.getErrorCode());
assertEquals('x', e.getErrorArgumentId());
}
}
public void testSimpleDoublePresent() throws Exception {
Args args = new Args("x##", new String[]{"-x", "42.3"});
assertEquals(1, args.cardinality());
assertTrue(args.has('x'));
assertEquals(42.3, args.getDouble('x'), .001);
}
public void testInvalidDouble() throws Exception {
try {
new Args("x##", new String[]{"-x", "Forty two"});
fail();
} catch (ArgsException e) {
assertEquals(ArgsException.ErrorCode.INVALID_DOUBLE, e.getErrorCode());
assertEquals('x', e.getErrorArgumentId());
assertEquals("Forty two", e.getErrorParameter());
}
}
public void testMissingDouble() throws Exception {
try {
new Args("x##", new String[]{"-x"});
fail();
} catch (ArgsException e) {
assertEquals(ArgsException.ErrorCode.MISSING_DOUBLE, e.getErrorCode());
assertEquals('x', e.getErrorArgumentId());
}
}
}
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Listing 14-14 ArgsExceptionTest.java
代码清单 14-14 ArgsExceptionTest.java
public class ArgsExceptionTest extends TestCase {
public void testUnexpectedMessage() throws Exception {
ArgsException e =
new ArgsException(ArgsException.ErrorCode.UNEXPECTED_ARGUMENT,
'x', null);
assertEquals("Argument -x unexpected.", e.errorMessage());
}
public void testMissingStringMessage() throws Exception {
ArgsException e = new ArgsException(ArgsException.ErrorCode.MISSING_STRING,
'x', null);
assertEquals("Could not find string parameter for -x.", e.errorMessage());
}
public void testInvalidIntegerMessage() throws Exception {
ArgsException e =
new ArgsException(ArgsException.ErrorCode.INVALID_INTEGER,
'x', "Forty two");
assertEquals("Argument -x expects an integer but was 'Forty two'.",
e.errorMessage());
}
public void testMissingIntegerMessage() throws Exception {
ArgsException e =
new ArgsException(ArgsException.ErrorCode.MISSING_INTEGER, 'x', null);
assertEquals("Could not find integer parameter for -x.", e.errorMessage());
}
public void testInvalidDoubleMessage() throws Exception {
ArgsException e = new ArgsException(ArgsException.ErrorCode.INVALID_DOUBLE,
'x', "Forty two");
assertEquals("Argument -x expects a double but was 'Forty two'.",
e.errorMessage());
}
public void testMissingDoubleMessage() throws Exception {
ArgsException e = new ArgsException(ArgsException.ErrorCode.MISSING_DOUBLE,
'x', null);
assertEquals("Could not find double parameter for -x.", e.errorMessage());
}
}
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Listing 14-15 ArgsException.java
代码清单 14-15 ArgsException.java
public class ArgsException extends Exception {
private char errorArgumentId = '\0';
private String errorParameter = "TILT";
private ErrorCode errorCode = ErrorCode.OK;
public ArgsException() {
}
public ArgsException(String message) {
super(message);
}
public ArgsException(ErrorCode errorCode) {
this.errorCode = errorCode;
}
public ArgsException(ErrorCode errorCode, String errorParameter) {
this.errorCode = errorCode;
this.errorParameter = errorParameter;
}
public ArgsException(ErrorCode errorCode, char errorArgumentId,
String errorParameter) {
this.errorCode = errorCode;
this.errorParameter = errorParameter;
this.errorArgumentId = errorArgumentId;
}
public char getErrorArgumentId() {
return errorArgumentId;
}
public void setErrorArgumentId(char errorArgumentId) {
this.errorArgumentId = errorArgumentId;
}
public String getErrorParameter() {
return errorParameter;
}
public void setErrorParameter(String errorParameter) {
this.errorParameter = errorParameter;
}
public ErrorCode getErrorCode() {
return errorCode;
}
public void setErrorCode(ErrorCode errorCode) {
this.errorCode = errorCode;
}
public String errorMessage() throws Exception {
switch (errorCode) {
case OK:
throw new Exception("TILT: Should not get here.");
case UNEXPECTED_ARGUMENT:
return String.format("Argument -%c unexpected.", errorArgumentId);
case MISSING_STRING:
return String.format("Could not find string parameter for -%c.",
errorArgumentId);
case INVALID_INTEGER:
return String.format("Argument -%c expects an integer but was '%s'.",
errorArgumentId, errorParameter);
case MISSING_INTEGER:
return String.format("Could not find integer parameter for -%c.",
errorArgumentId);
case INVALID_DOUBLE:
return String.format("Argument -%c expects a double but was '%s'.",
errorArgumentId, errorParameter);
case MISSING_DOUBLE:
return String.format("Could not find double parameter for -%c.",
errorArgumentId);
}
return "";
}
public enum ErrorCode {
OK, INVALID_FORMAT, UNEXPECTED_ARGUMENT, INVALID_ARGUMENT_NAME,
MISSING_STRING,
MISSING_INTEGER, INVALID_INTEGER,
MISSING_DOUBLE, INVALID_DOUBLE
}
}
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Listing 14-16 Args.java
代码清单 14-16 Args.java
public class Args {
private String schema;
private Map<Character, ArgumentMarshaler> marshalers =
new HashMap<Character, ArgumentMarshaler>();
private Set<Character> argsFound = new HashSet<Character>();
private Iterator<String> currentArgument;
private List<String> argsList;
public Args(String schema, String[] args) throws ArgsException {
this.schema = schema;
argsList = Arrays.asList(args);
parse();
}
private void parse() throws ArgsException {
parseSchema();
parseArguments();
}
private boolean parseSchema() throws ArgsException {
for (String element : schema.split(",")) {
if (element.length() > 0) {
parseSchemaElement(element.trim());
}
}
return true;
}
private void parseSchemaElement(String element) throws ArgsException {
char elementId = element.charAt(0);
String elementTail = element.substring(1);
validateSchemaElementId(elementId);
if (elementTail.length() == 0)
marshalers.put(elementId, new BooleanArgumentMarshaler());
else if (elementTail.equals("*"))
marshalers.put(elementId, new StringArgumentMarshaler());
else if (elementTail.equals("#"))
marshalers.put(elementId, new IntegerArgumentMarshaler());
else if (elementTail.equals("##"))
marshalers.put(elementId, new DoubleArgumentMarshaler());
else
throw new ArgsException(ArgsException.ErrorCode.INVALID_FORMAT,
elementId, elementTail);
}
private void validateSchemaElementId(char elementId) throws ArgsException {
if (!Character.isLetter(elementId)) {
throw new ArgsException(ArgsException.ErrorCode.INVALID_ARGUMENT_NAME,
elementId, null);
}
}
private void parseArguments() throws ArgsException {
for (currentArgument = argsList.iterator(); currentArgument.hasNext(); ) {
String arg = currentArgument.next();
parseArgument(arg);
}
}
private void parseArgument(String arg) throws ArgsException {
if (arg.startsWith("-"))
parseElements(arg);
}
private void parseElements(String arg) throws ArgsException {
for (int i = 1; i < arg.length(); i++)
parseElement(arg.charAt(i));
}
private void parseElement(char argChar) throws ArgsException {
if (setArgument(argChar))
argsFound.add(argChar);
else {
throw new ArgsException(ArgsException.ErrorCode.UNEXPECTED_ARGUMENT,
argChar, null);
}
}
private boolean setArgument(char argChar) throws ArgsException {
ArgumentMarshaler m = marshalers.get(argChar);
if (m == null)
return false;
try {
m.set(currentArgument);
return true;
} catch (ArgsException e) {
e.setErrorArgumentId(argChar);
throw e;
}
}
public int cardinality() {
return argsFound.size();
}
public String usage() {
if (schema.length() > 0)
return "-[" + schema + "]";
else
return "";
}
public boolean getBoolean(char arg) {
ArgumentMarshaler am = marshalers.get(arg);
boolean b = false;
try {
b = am != null && (Boolean) am.get();
} catch (ClassCastException e) {
b = false;
}
return b;
}
public String getString(char arg) {
ArgumentMarshaler am = marshalers.get(arg);
try {
return am == null ? "" : (String) am.get();
} catch (ClassCastException e) {
return "";
}
}
public int getInt(char arg) {
ArgumentMarshaler am = marshalers.get(arg);
try {
return am == null ? 0 : (Integer) am.get();
} catch (Exception e) {
return 0;
}
}
public double getDouble(char arg) {
ArgumentMarshaler am = marshalers.get(arg);
try {
return am == null ? 0 : (Double) am.get();
} catch (Exception e) {
return 0.0;
}
}
public boolean has(char arg) {
return argsFound.contains(arg);
}
}
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The majority of the changes to the Args class were deletions. A lot of code just got moved out of Args and put into ArgsException. Nice. We also moved all the ArgumentMarshaller s into their own files. Nicer!
对 Args 类所做的最主要的修改是在监测部分。从 Args 里面取出了大量代码，放到 ArgsException 中。很好。我们还把全部 ArgumentMarshaler 转移到了它们自己的文件中。更好！
Much of good software design is simply about partitioning—creating appropriate places to put different kinds of code. This separation of concerns makes the code much simpler to understand and maintain.
优秀的软件设计，大都关乎分隔——创建合适的空间放置不同种类的代码。对关注面的分隔让代码更易于理解和维护。
Of special interest is the errorMessage method of ArgsException. Clearly it was a violation of the SRP to put the error message formatting into Args. Args should be about the processing of arguments, not about the format of the error messages. However, does it really make sense to put the error message formatting code into ArgsException?
特别有意思的是 ArgsException 中的 errorMessage 方法。显然，把错误信息格式化操作放在 Args 里面，违反了 SRP 原则。Args 应该只处理参数，不该去管错误信息的格式。然而，把错误信息格式化代码放到 ArgsException 中是否有道理呢？
Frankly, it’s a compromise. Users who don’t like the error messages supplied by ArgsException will have to write their own. But the convenience of having canned error messages already prepared for you is not insignificant.
实话说，这是种折衷做法。不打算用 ArgsException 提供的错误信息的用户会想自己写错误信息。但如果有备好的错误信息，其方便之处也并非鲜见。
By now it should be clear that we are within striking distance of the final solution that appeared at the start of this chapter. I’ll leave the final transformations to you as an exercise.
现在，显然我们已经非常接近本章开始处所展示的最终解决方案了。最后的工作留给你来练习完成。
# 14.4 CONCLUSION 小结
It is not enough for code to work. Code that works is often badly broken. Programmers who satisfy themselves with merely working code are behaving unprofessionally. They may fear that they don’t have time to improve the structure and design of their code, but I disagree. Nothing has a more profound and long-term degrading effect upon a development project than bad code. Bad schedules can be redone, bad requirements can be redefined. Bad team dynamics can be repaired. But bad code rots and ferments, becoming an inexorable weight that drags the team down. Time and time again I have seen teams grind to a crawl because, in their haste, they created a malignant morass of code that forever thereafter dominated their destiny.
代码能工作还不够。能工作的代码经常会严重崩溃。满足于仅仅让代码能工作的程序员不够专业。他们会害怕没时间改进代码的结构和设计，我不敢苟同。没什么能比糟糕的代码给开发项目带来更深远和长期的损害了。进度可以重订，需求可以重新定义，团队动态可以修正。但糟糕的代码只是一直腐败发酵，无情地拖着团队的后腿。我无数次看到开发团队蹒跚前行，只因为他们匆匆搞出一片代码沼泽，从此之后命运再也不受自己控制。
Of course bad code can be cleaned up. But it’s very expensive. As code rots, the modules insinuate themselves into each other, creating lots of hidden and tangled dependencies. Finding and breaking old dependencies is a long and arduous task. On the other hand, keeping code clean is relatively easy. If you made a mess in a module in the morning, it is easy to clean it up in the afternoon. Better yet, if you made a mess five minutes ago, it’s very easy to clean it up right now.
当然，糟糕的代码可以清理。不过成本高昂。随着代码腐败下去，模块之间互相渗透，出现大量隐藏纠结的依赖关系。找到和破除陈旧的依赖关系又费时间又费劲。另一方面，保持代码整洁却相对容易。早晨在模块中制造出一堆混乱，下午就能轻易清理掉。更好的情况是，5 分钟之前制造出混乱，马上就能很容易地清理掉。
So the solution is to continuously keep your code as clean and simple as it can be. Never let the rot get started.
所以，解决之道就是保持代码持续整洁和简单。永不让腐坏有机会开始。