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Args4J 使用指南

Args4J 是一個用來出來命令行的工具.

在實際的項目中用到命令行的并不是很常見,但當真正使用到時,特別是在程序啟動時配置一下參數的時候就很有用了,如果參數很多的話,一個一個解析命令行還是比較麻煩的.這時使用Args4J就相當好辦了. 在本文中我們來看看Args4J的使用,當需要時能提供一個解決方案.

Args4J使用一個被稱為Option類的類來保存輸入的參數,讓后根據該類來應用參數,每個參數可以對應一個類中的屬性,該屬性用Annotation注釋,在Annotation中給出該參數 的選項, 還可以配置其他有用的信息.該Annotation就是 Option 注解: 該注解的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 (see AccessibleObject.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.

該注解有5各域 其中name是必須的,其他四個是可選的.如下所示,關于該注解的詳細Doc請查看 其docs.

當命令行設定后 其使用方式和java 命令里面的參數使用方式一樣 如:java -cp ./calssPath/.......

下面通過一個例子來解釋:

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注解來定義一個boolean?命令行參數?其參數name為?-re?,required指定該參數是必須的
021???@Option(name?=?"-re",?usage?=?"recursively?run?something",?required?=?true)
022???private?boolean?recursive;
023?
024???//利用Option注解定義一個File?命令行參數,?name為-o,?輸入時候知道該file的路徑就可以了
025???//metaVar?用來設定顯示?使用方式時候的輸出,這個輸出為-o?OUTPUT?:?output?to?this?file
026???//如果不指定該屬性?則使用默認的代替?為-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???//注意該處沒有指定?usage?屬性?或者指定usage?但是其值為空的?如usage?=?"",這樣當使用
033???//parser.printExample(ExampleMode.ALL)?請注意下面第92行的輸出
034???@Option(name?=?"-str",?required?=?true)
035???//@Option(name?=?"-str",?usage?=?"測試",?required?=?true)??//?該行?-str參數有用
036???//?no?usage
037???
038???private?String?str?=?"(default?value)";
039?
040???//?整數參數
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???//指定一個特定的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());??//打印出錯消息
080???????System.err.println("java?SampleMain?[options...]?arguments...");
081???????//?print?the?list?of?available?options
082???????parser.printUsage(System.err);??//?打印參數的用法
083???????System.err.println();
084?
085???????System.err.println("測試!!!!!");
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中如果沒有指定 usage 屬性,
089???????System.err.println("/n?2.........");???????????????

//則這兩行程序不會輸出該參數的使用的
090?
091???????System.err.println("?2?Example2:?java?SampleMain"?

//注意 在Option中如果沒有指定 usage 屬性,
092???????????+?parser.printExample(ExampleMode.REQUIRED));??

//則這兩行程序不會輸出該參數的使用的
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?}

當不使用命令行時候 輸入信息如下:

當使用 -re 為命令行輸入時,輸出如下:// 后為作者加的注釋 不是輸出

當使用-re -str some 為命令行輸入時,結果如下:這是由于的73 行的判斷引起的

使用-custom -n 2 -re -str some otherstring 為命令行輸入時的 結果如下:

當使用-custom -n 2 -re -str some -o log.txt otherstring 時候的輸出如下:

當使用一個不存在的參數時候 會有Exception的 例如:-custom -ee 2 -re -str some -o log.txt otherstring

其中-ee參數不存在 結果如下:

......

由以上的實例可以看出 args4J 取得命令行的輸入參數,然后根據保存參數的類中的屬性類型比較
?
并轉換為適當的值, 然后我們可以使用這些屬性了,這樣就免去了自己判斷args 的麻煩了,

當默認的Handler不滿足你的要求時 可以自己擴展Handler實現,關于這點請參考Args4J的測試用例,

From : java 愛好者? by : icess