Args4J 使用指南
在实际的项目中用到命令行的并不是很常见,但当真正使用到时,特别是在程序启动时配置一下参数的时候就很有用了,如果参数很多的话,一个一个解析命令行还是比较麻烦的.这时使用Args4J就相当好办了. 在本文中我们来看看Args4J的使用,当需要时能提供一个解决方案.
Args4J使用一个被称为Option类的类来保存输入的参数,让后根据该类来应用参数,每个参数可以对应一个类中的属性,该属性用Annotation注释,在Annotation中给出该参数 的选项, 还可以配置其他有用的信息.该Annotation就是 Option 注解: 该注解的doc如下:
Marks a field/setter that receives a command line switch value.
This annotation can be placed on a field of type T or the method of the form void methodName(T value). Its access modified can be anything, but if it's not public, your application needs to run in a security context that allows args4j to access the field/method (seeAccessibleObject.setAccessible(boolean).
The behavior of the annotation differs depending on T --- the type of the field or the parameter of the method.
Boolean Switch
When T is boolean , it represents a boolean option that takes the form of "-OPT". When this option is set, the property will be set to true.
String Switch
When T is String, it represents an option that takes one operand. The value of the operand is set to the property.
Enum Switch
When T is derived from Enum, it represents an option that takes an operand, which must be one of the enum constant. The comparion between the operand and the enum constant name is done in a case insensitive fashion.
For example, the following definition will represent command line options like "-coin penny" or "-coin DIME" but things like "-coin" or "-coin abc" are errors.
enum Coin { PENNY,NICKEL,DIME,QUARTER }
class Option {
@Option(name="-coin")
public Coin coin;
}
File Switch
When T is a File, it represents an option that takes a file/directory name as an operand.
该注解有5各域 其中name是必须的,其他四个是可选的.如下所示,关于该注解的详细Doc请查看 其docs.
| Required Element Summary | |
|---|---|
String | nameName of the option, such as "-foo" or "-bar". |
| Optional Element Summary | |
|---|---|
Class<? extendsOptionHandler> | handlerSpecify the OptionHandler that processes the command line arguments. |
String | metaVarWhen the option takes an operand, the usage screen will show something like this: |
boolean | requiredSpecify that the option is mandatory. |
String | usageHelp string used to display the usage screen. |
当命令行设定后 其使用方式和java 命令里面的参数使用方式一样 如:java -cp ./calssPath/.......
下面通过一个例子来解释:
001 /*
002 * Created on 2006-2-21
003 * @author icerain
004 */
005 package test.args4j;
006
007 import org.kohsuke.args4j.Argument;
008 import org.kohsuke.args4j.CmdLineException;
009 import org.kohsuke.args4j.CmdLineParser;
010 import org.kohsuke.args4j.ExampleMode;
011 import org.kohsuke.args4j.Option;
012 import org.kohsuke.args4j.spi.BooleanOptionHandler;
013
014 import java.io.File;
015 import java.io.IOException;
016 import java.util.ArrayList;
017 import java.util.List;
018
019 public class TestArgs4J {
020 // 利用Option注解来定义一个boolean 命令行参数 其参数name为 -re ,required指定该参数是必须的
021 @Option(name = "-re", usage = "recursively run something", required = true)
022 private boolean recursive;
023
024 //利用Option注解定义一个File 命令行参数, name为-o, 输入时候知道该file的路径就可以了
025 //metaVar 用来设定显示 使用方式时候的输出,这个输出为-o OUTPUT : output to this file
026 //如果不指定该属性 则使用默认的代替 为-o FILE : output to this file
027 @Option(name = "-o", usage = "output to this file", metaVar = "OUTPUT")
028 private File out = new File(".");
029
030 //If 'usage' value is empty, the option will not be displayed
031 // in the usage screen.
032 //注意该处没有指定 usage 属性 或者指定usage 但是其值为空的 如usage = "",这样当使用
033 //parser.printExample(ExampleMode.ALL) 请注意下面第92行的输出
034 @Option(name = "-str", required = true)
035 //@Option(name = "-str", usage = "测试", required = true) // 该行 -str参数有用
036 // no usage
037
038 private String str = "(default value)";
039
040 // 整数参数
041 @Option(name = "-n", usage = "repeat <n> times\nusage can have new lines in it and also it can be verrry long")
042 private int num = -1;
043
044 // using 'handler=...' allows you to specify a custom OptionHandler
045 // implementation class. This allows you to bind a standard Java type
046 // with a non-standard option syntax
047 //指定一个特定的handler
048 @Option(name = "-custom", handler=BooleanOptionHandler.class,usage="boolean value for checking the custom handler")
049 private boolean data;
050
051 // receives other command line parameters than options
052 @Argument
053 private List<String> arguments = new ArrayList<String>();
054
055 public static void main(String[] args) throws IOException {
056 new TestArgs4J().doMain(args);
057 }
058
059 public void doMain(String[] args) throws IOException {
060 //Creates a new command line owner that parses arguments/options
and set them into the given object.
061 CmdLineParser parser = new CmdLineParser(this);
062
063 try {
064 // parse the arguments.
065 parser.parseArgument(args);
066
067 // you can parse additional arguments if you want.
068 // parser.parseArgument("more","args");
069
070 // after parsing arguments, you should check
071 // if enough arguments are given.
072 if (arguments.isEmpty())
073 throw new CmdLineException("No argument is given");
074
075 } catch (CmdLineException e) {
076 // if there's a problem in the command line,
077 // you'll get this exception. this will report
078 // an error message.
079 System.err.println(e.getMessage()); //打印出错消息
080 System.err.println("java SampleMain [options...] arguments...");
081 // print the list of available options
082 parser.printUsage(System.err); // 打印参数的用法
083 System.err.println();
084
085 System.err.println("测试!!!!!");
086 // print option sample. This is useful some time
087 System.err.println(" Example: java SampleMain"
088 + parser.printExample(ExampleMode.ALL));
// 注意 在Option中如果没有指定 usage 属性,
089 System.err.println("/n 2.........");
//则这两行程序不会输出该参数的使用的
090
091 System.err.println(" 2 Example2: java SampleMain"
//注意 在Option中如果没有指定 usage 属性,
092 + parser.printExample(ExampleMode.REQUIRED));
//则这两行程序不会输出该参数的使用的
093 return;
094 }
095
096 // this will redirect the output to the specified output
097 System.out.println(out);
098
099 if (recursive)
100 System.out.println("-r flag is set");
101
102 if (data)
103 System.out.println("-custom flag is set");
104
105 System.out.println("-str was " + str);
106
107 if (num >= 0)
108 System.out.println("-n was " + num);
109
110 // access non-option arguments
111 System.out.println("other arguments are:");
112 for (String s : arguments)
113 System.out.println(s);
114 }
115
116 }
当不使用命令行时候 输入信息如下:
Option "-re" is required
java SampleMain [options...] arguments...
-custom : boolean value for checking the custom handler
-n N : repeat <n> times
usage can have new lines in it and also it can be verrrrrrr
rrrrrrrrrrry long
-o OUTPUT : output to this file
-re : recursively run something
测试!!!!!
Example: java SampleMain -custom -n N -o OUTPUT -re
// 注意该处没有 -str的出现/n 2.........
2 Example2: java SampleMain -re
// 注意该处没有 -str的出现当使用 -re 为命令行输入时,输出如下:// 后为作者加的注释 不是输出
Option "-str" is required
//也要指定-str该参数java SampleMain [options...] arguments...
-custom : boolean value for checking the custom handler
-n N : repeat <n> times
usage can have new lines in it and also it can be verrrrrrr
rrrrrrrrrrry long
-o OUTPUT : output to this file
-re : recursively run something
测试!!!!!
Example: java SampleMain -custom -n N -o OUTPUT -re
/n 2.........
2 Example2: java SampleMain -re
当使用-re -str some 为命令行输入时,结果如下:这是由于的73 行的判断引起的
No argument is given
java SampleMain [options...] arguments...
-custom : boolean value for checking the custom handler
-n N : repeat <n> times
usage can have new lines in it and also it can be verrrrrrr
rrrrrrrrrrry long
-o OUTPUT : output to this file
-re : recursively run something
测试!!!!!
Example: java SampleMain -custom -n N -o OUTPUT -re
/n 2.........
2 Example2: java SampleMain -re
使用-custom -n 2 -re -str some otherstring 为命令行输入时的 结果如下:
. // file
-r flag is set
-custom flag is set
-str was some
-n was 2
other arguments are:
otherstring
当使用-custom -n 2 -re -str some -o log.txt otherstring 时候的输出如下:
log.txt
-r flag is set
-custom flag is set
-str was some
-n was 2
other arguments are:
otherstring
当使用一个不存在的参数时候 会有Exception的 例如:-custom -ee 2 -re -str some -o log.txt otherstring
其中-ee参数不存在 结果如下:
"-ee" is not a valid option
java SampleMain [options...] arguments...
-custom : boolean value for checking the custom handler
-n N : repeat <n> times
......
由以上的实例可以看出 args4J 取得命令行的输入参数,然后根据保存参数的类中的属性类型比较
并转换为适当的值, 然后我们可以使用这些属性了,这样就免去了自己判断args 的麻烦了,
当默认的Handler不满足你的要求时 可以自己扩展Handler实现,关于这点请参考Args4J的测试用例,