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[#]: subject: "Parse command options in Java with commons-cli"
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[#]: via: "https://opensource.com/article/21/8/java-commons-cli"
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[#]: author: "Seth Kenlon https://opensource.com/users/seth"
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[#]: collector: "lujun9972"
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[#]: translator: "unigeorge"
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[#]: reviewer: " "
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[#]: publisher: " "
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[#]: url: " "
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Parse command options in Java with commons-cli
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======
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Let your users modify how your Java application runs with command-line
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options.
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![Learning and studying technology is the key to success][1]
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When you enter a command into your terminal, whether it's to launch a GUI app or just a terminal app, there are often [options][2] (sometimes called _switches_ or _flags_) you can use to modify how the application runs. This is a standard set by the [POSIX specification][3], so it's useful for a Java programmer to know how to detect and parse options.
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There are several ways to parse options in Java. My favorite is the [Apache Commons CLI][4] library, called **commons-cli** for short.
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### Installing commons-cli
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If you're using a project management system like [Maven][5] and an IDE, you can install the Apache Commons CLI library in your project properties (such as `pom.xml` or a configuration screen in Eclipse or NetBeans).
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If you're managing libraries manually, you can download [the latest release][6] from the Apache website. Several JAR files come bundled together. The only required JAR is the `commons-cli-X.Y.jar` (where X and Y are the latest version numbers.) Add that JAR to your project, either manually or in your IDE, and then you can use it in your code.
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### Importing a library into your Java code
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To use the **commons-cli** library in your code, you must import it. For this simple option parsing example, you can populate a file called `Main.java` with the standard minimal code:
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```
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package com.opensource.myoptparser;
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import org.apache.commons.cli.*;
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public class Main {
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public static void main([String][7][] args) {
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// code
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}
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}
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```
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Now you're set to parse options in Java.
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### Defining Boolean options in Java
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The first thing you must do to parse options is to define the valid options your application can accept. Use the `Option` (singular) class to create option objects and the `Options` (plural) class to help keep track of all the options you've created in your project.
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First, create a group for your options, and call it `options` according to convention:
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```
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//code
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Options options = new Options();
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```
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Next, define your individual options by listing a short option, a long option, a default Boolean value, and a help message. You then set whether the option is required or not, and finally add the option to the `options` object, which contains all of your options. In this example, I create just one option, arbitrarily called `alpha`:
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```
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//define options
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[Option][8] alpha = new [Option][8]("a", "alpha", false, "Activate feature alpha");
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options.addOption(alpha);
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```
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### Defining options with arguments in Java
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Sometimes you want users to provide information other than just **true** or **false** along with an option. You might want to let a user refer to a configuration file, an input file, or any setting like a date or a color. For this, you use the `builder` method, creating attributes for an option based on its short version (for example, `-c` is a short option, `--config` is a long option). Once it's defined, you add the new option to your `options` group:
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```
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[Option][8] config = [Option][8].builder("c").longOpt("config")
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.argName("config")
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.hasArg()
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.required(true)
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.desc("set config file").build();
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options.addOption(config);
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```
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With the `builder` function, you can set the short version, long version, whether it's required (I set this to **true** in this code, so my application can't run unless this option is provided by the user at launch time), the help message, and so on.
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### Parsing options with Java
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With all possible options defined, you can now iterate over arguments provided by the user, checking to see whether any argument matches your approved list of valid short options. To do this, you create an instance of the **CommandLine** itself, which contains all arguments provided by the user (valid options and otherwise.) You also create a **CommandLineParser** object, which I call `parser` in my code, to facilitate interaction over those arguments. Finally, you can create a **HelpFormatter** object (which I call `helper`) to automatically provide helpful messages to the user when either a required option is missing, or the `--help` or `-h` option is used.
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```
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// define parser
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CommandLine cmd;
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CommandLineParser parser = new BasicParser();
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HelpFormatter helper = new HelpFormatter();
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```
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Finally, add some conditionals to analyze the options provided by the user as command-line input (discovered and stored in the `cmd` variable). This sample application has two different types of options, but in both cases, you can check whether the option exists with the `.hasOption` method plus the short option name. When an option is detected, you can do whatever needs to be done with the data.
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```
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try {
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cmd = parser.parse(options, args);
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if(cmd.hasOption("a")) {
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[System][9].out.println("Alpha activated");
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}
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if (cmd.hasOption("c")) {
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[String][7] opt_config = cmd.getOptionValue("config");
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[System][9].out.println("Config set to " + opt_config);
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}
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} catch ([ParseException][10] e) {
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[System][9].out.println(e.getMessage());
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helper.printHelp("Usage:", options);
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[System][9].exit(0);
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}
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```
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The act of parsing potentially generates an error because sometimes the required `-c` or `--config` option could be missing. In that event, a help message is printed, and the application is immediately ended. Because of this error (an _exception_ in Java terminology), you must amend the start of the main method to declare a possible exception:
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```
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`public static void main(String[] args) throws ParseException {`
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```
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The sample application is now complete.
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### Test your code
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You can test the application in your IDE by adjusting the default parameters passed to your code or just build a JAR file and run it from your terminal. The process for this differs depending on your IDE. Refer to your IDE documentation, read my article on how to LINK-TO-ARTICLE[build a JAR], or see Daniel Oh's article on how to do the same with [Maven][11].
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First, confirm the parser exception by omitting the required `-c` or `--config` option:
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```
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$ java -jar dist/myapp.jar
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Missing required option: c
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usage: Usage:
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-a,--alpha Activate feature alpha
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-c,--config <config> Set config file
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```
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Try it again with the options provided:
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```
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java -jar dist/myantapp.jar --config foo -a
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Alpha activated
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Config set to foo
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```
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### Option parsing
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Including options for your users is an important feature for any application. Java and the Apache commons make it easy to do.
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Here's the full demonstration code for your reference:
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```
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package com.opensource.myapp;
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import org.apache.commons.cli.*;
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public class Main {
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/**
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* @param args the command line arguments
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* @throws org.apache.commons.cli.ParseException
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*/
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public static void main([String][7][] args) throws [ParseException][10] {
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// define options
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Options options = new Options();
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[Option][8] alpha = new [Option][8]("a", "alpha", false, "Activate feature alpha");
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options.addOption(alpha);
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[Option][8] config = [Option][8].builder("c").longOpt("config")
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.argName("config")
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.hasArg()
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.required(true)
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.desc("Set config file").build();
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options.addOption(config);
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// define parser
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CommandLine cmd;
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CommandLineParser parser = new BasicParser();
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HelpFormatter helper = new HelpFormatter();
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try {
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cmd = parser.parse(options, args);
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if(cmd.hasOption("a")) {
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[System][9].out.println("Alpha activated");
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}
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if (cmd.hasOption("c")) {
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[String][7] opt_config = cmd.getOptionValue("config");
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[System][9].out.println("Config set to " + opt_config);
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}
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} catch ([ParseException][10] e) {
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[System][9].out.println(e.getMessage());
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helper.printHelp("Usage:", options);
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[System][9].exit(0);
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}
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}
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}
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```
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### Using Java and options
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Options allow users to modify how commands work. There are many ways to parse options when using Java, and the `commons-cli` is a robust and flexible open source solution. Give it a try in your next Java project.
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--------------------------------------------------------------------------------
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via: https://opensource.com/article/21/8/java-commons-cli
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作者：[Seth Kenlon][a]
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选题：[lujun9972][b]
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译者：[unigeorge](https://github.com/unigeorge)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]: https://opensource.com/users/seth
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[b]: https://github.com/lujun9972
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[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/lead-images/studying-books-java-couch-education.png?itok=C9gasCXr (Learning and studying technology is the key to success)
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[2]: https://opensource.com/article/21/8/linux-terminal#options
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[3]: https://opensource.com/article/19/7/what-posix-richard-stallman-explains
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[4]: https://commons.apache.org/proper/commons-cli/usage.html
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[5]: https://maven.apache.org/
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[6]: https://commons.apache.org/proper/commons-cli/download_cli.cgi
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[7]: http://www.google.com/search?hl=en&q=allinurl%3Adocs.oracle.com+javase+docs+api+string
|
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[8]: http://www.google.com/search?hl=en&q=allinurl%3Adocs.oracle.com+javase+docs+api+option
|
||||
[9]: http://www.google.com/search?hl=en&q=allinurl%3Adocs.oracle.com+javase+docs+api+system
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[10]: http://www.google.com/search?hl=en&q=allinurl%3Adocs.oracle.com+javase+docs+api+parseexception
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[11]: https://developers.redhat.com/blog/2021/04/08/build-even-faster-quarkus-applications-with-fast-jar
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@ -0,0 +1,226 @@
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[#]: subject: "Parse command options in Java with commons-cli"
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[#]: via: "https://opensource.com/article/21/8/java-commons-cli"
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[#]: author: "Seth Kenlon https://opensource.com/users/seth"
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[#]: collector: "lujun9972"
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[#]: translator: "unigeorge"
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[#]: reviewer: " "
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[#]: publisher: " "
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[#]: url: " "
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使用 commons-cli 解析 Java 中的命令行选项
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======
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让用户学会用命令行选项调整你的 Java 应用程序运行方式。
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![Learning and studying technology is the key to success][1]
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通常向终端中输入命令时，无论是启动 GUI 应用程序还是仅启动终端应用程序，都可以使用
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<ruby>
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[命令行选项][2]<rp>(</rp><rt>options or switches or flags</rt><rp>)</rp>
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</ruby>
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（**以下简称选项**）来修改应用程序的运行方式。这是 [POSIX 规范][3] 设定的标准，因此能够检测和解析选项对 Java 程序员而言是很有用的技能。
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Java 中有若干种解析选项的方法，其中我最喜欢用的是 [Apache Commons CLI][4] 库，简称 **commons-cli**。
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### 安装 commons-cli
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如果你使用类似 [Maven][5] 之类的项目管理系统以及集成开发环境（Integrated Development Environment，简称IDE），可以在项目属性（比如 `pom.xml` 配置文件或者 Eclipse 和 NetBeans 的配置选项卡）中安装 Apache Commons CLI 库。
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而如果你采用手动方式管理库，则可以从 Apache 网站下载 [该库的最新版本][6]。下载到本地的是几个捆绑在一起的 JAR 文件，你只需要其中的一个文件 `commons-cli-X.Y.jar`（其中 X 和 Y 代指最新版本号）。把这个 JAR 文件或手动或使用 IDE 添加到项目，就可以在代码中使用了。
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### 将库导入至 Java 代码
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在使用 **commons-cli** 库之前，必须首先导入它。对于本次选项解析的简单示例而言，可以先在 `Main.java` 文件中简单写入以下标准代码：
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```
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package com.opensource.myoptparser;
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import org.apache.commons.cli.*;
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public class Main {
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public static void main([String][7][] args) {
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// code
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}
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}
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```
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至此在 Java 中解析选项的准备工作已经做好了。
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### 在 Java 中定义布尔选项
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要实现解析选项，首先要定义应用程序可接收的有效选项。使用 `Option`（注意是单数）类来创建选项对象，使用 `Options`（注意是复数）类来追踪项目中创建的所有选项。
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首先为选项创建一个组，按照惯例命名为 `options`：
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```
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//code
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Options options = new Options();
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```
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接下来，通过列出短选项（即选项名简写）、长选项（即全写）、默认布尔值（译注：设置是否需要选项参数，指定为 false 时此选项不带参，即为布尔选项）和帮助信息来定义选项，然后设置该选项是否为必需项（译注：下方创建 `alpha` 对象的代码中未手动设置此项），最后将该选项添加到包含所有选项的 `options` 组对象中。在下面几行代码中，我只创建了一个选项，命名为 `alpha`：
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```
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//define options
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[Option][8] alpha = new [Option][8]("a", "alpha", false, "Activate feature alpha");
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options.addOption(alpha);
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```
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### 在 Java 中定义带参选项
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有时用户需要通过选项提供 **true** 或 **false** 以外的信息，比如给出配置文件、输入文件或诸如日期、颜色这样的设置项值。这种情况可以使用 `builder` 方法，根据选项名简写为其创建属性（例如，`-c` 是短选项，`--config` 是长选项）。完成定义后，再将定义好的选项添加到 `options` 组中：
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```
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[Option][8] config = [Option][8].builder("c").longOpt("config")
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.argName("config")
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.hasArg()
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.required(true)
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.desc("set config file").build();
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options.addOption(config);
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```
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`builder`函数可以用来设置短选项、长选项、是否为必需项（本段代码中必需项设置为 **true**，也就意味着用户启动程序时必须提供此选项，否则应用程序无法运行）、帮助信息等。
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### 使用 Java 解析选项
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定义并添加所有可能用到的选项后，需要对用户提供的参数进行迭代处理，检测是否有参数同预设的有效短选项列表中的内容相匹配。为此要创建 **CommandLine** 命令行本身的一个实例，其中包含用户提供的所有参数（包含有效选项和无效选项）。为了处理这些参数，还要创建一个 **CommandLineParser** 对象，我在代码中将其命名为 `parser`。最后，还可以创建一个 **HelpFormatter** 对象（我将其命名为 `helper`），当参数中缺少某些必需项或者用户使用 `--help` 或 `-h` 选项时，此对象可以自动向用户提供一些有用的信息。
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```
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// define parser
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CommandLine cmd;
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CommandLineParser parser = new BasicParser();
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HelpFormatter helper = new HelpFormatter();
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```
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最后，添加一些条件判断来分析用户提供的选项，我们假设这些选项已经作为命令行输入被获取并存储在 `cmd` 变量中。这个示例应用程序有两种不同类型的选项，但对这两种类型都可以使用 `.hasOption` 方法加上短选项名称来检测选项是否存在。检测到一个存在的选项后，就可以对数据做进一步操作了。
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```
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try {
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cmd = parser.parse(options, args);
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||||
if(cmd.hasOption("a")) {
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[System][9].out.println("Alpha activated");
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}
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||||
if (cmd.hasOption("c")) {
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[String][7] opt_config = cmd.getOptionValue("config");
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[System][9].out.println("Config set to " + opt_config);
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}
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} catch ([ParseException][10] e) {
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[System][9].out.println(e.getMessage());
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helper.printHelp("Usage:", options);
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[System][9].exit(0);
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}
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```
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解析过程有可能会产生错误，因为有时可能缺少某些必需项如本例中的 `-c` 或 `--config` 选项。这时程序会打印一条帮助信息，并立即结束运行。考虑到此错误（Java 术语中称为 _exception_，异常），在 main 方法的开头要添加语句声明可能的异常：
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||||
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||||
```
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public static void main(String[] args) throws ParseException {
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||||
```
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示例程序至此就大功告成了。
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### 测试代码
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你可以通过调整传递给代码的默认参数来在 IDE 中测试应用程序，或者创建一个 JAR 文件并在终端运行测试。这个过程可能会因 IDE 的不同而不同。具体请参阅相应的 IDE 文档，以及我写过的关于如何创建 JAR 文件的文章，或者参考 Daniel Oh 的关于如何使用 [Maven][11] 执行同样操作的文章。
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首先，省略必需项 `-c` 或 `--config` 选项，检测解析器的异常处理：
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```
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$ java -jar dist/myapp.jar
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Missing required option: c
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||||
usage: Usage:
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||||
-a,--alpha Activate feature alpha
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||||
-c,--config <config> Set config file
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||||
```
|
||||
|
||||
然后提供输入选项再进行测试：
|
||||
|
||||
```
|
||||
java -jar dist/myantapp.jar --config foo -a
|
||||
Alpha activated
|
||||
Config set to foo
|
||||
```
|
||||
|
||||
### 选项解析
|
||||
|
||||
为用户提供选项功能对任何应用程序来说都是很重要的。有了 Java 和 Apache Commons，要实现这个功能并不难。
|
||||
|
||||
以下是完整的演示代码，供读者参考：
|
||||
|
||||
|
||||
```
|
||||
package com.opensource.myapp;
|
||||
|
||||
import org.apache.commons.cli.*;
|
||||
|
||||
public class Main {
|
||||
|
||||
/**
|
||||
* @param args the command line arguments
|
||||
* @throws org.apache.commons.cli.ParseException
|
||||
*/
|
||||
public static void main([String][7][] args) throws [ParseException][10] {
|
||||
// define options
|
||||
Options options = new Options();
|
||||
|
||||
[Option][8] alpha = new [Option][8]("a", "alpha", false, "Activate feature alpha");
|
||||
options.addOption(alpha);
|
||||
|
||||
[Option][8] config = [Option][8].builder("c").longOpt("config")
|
||||
.argName("config")
|
||||
.hasArg()
|
||||
.required(true)
|
||||
.desc("Set config file").build();
|
||||
options.addOption(config);
|
||||
|
||||
// define parser
|
||||
CommandLine cmd;
|
||||
CommandLineParser parser = new BasicParser();
|
||||
HelpFormatter helper = new HelpFormatter();
|
||||
|
||||
try {
|
||||
cmd = parser.parse(options, args);
|
||||
if(cmd.hasOption("a")) {
|
||||
[System][9].out.println("Alpha activated");
|
||||
}
|
||||
|
||||
if (cmd.hasOption("c")) {
|
||||
[String][7] opt_config = cmd.getOptionValue("config");
|
||||
[System][9].out.println("Config set to " + opt_config);
|
||||
}
|
||||
} catch ([ParseException][10] e) {
|
||||
[System][9].out.println(e.getMessage());
|
||||
helper.printHelp("Usage:", options);
|
||||
[System][9].exit(0);
|
||||
}
|
||||
}
|
||||
}
|
||||
```
|
||||
|
||||
### 使用 Java 和选项
|
||||
|
||||
选项使用户可以调整命令的工作方式。使用 Java 时解析选项的方法有很多，其中之一的 `commons-cli` 是一个强大而灵活的开源解决方案。记得在你的下一个 Java 项目中尝试一下哦。
|
||||
|
||||
--------------------------------------------------------------------------------
|
||||
|
||||
via: https://opensource.com/article/21/8/java-commons-cli
|
||||
|
||||
作者：[Seth Kenlon][a]
|
||||
选题：[lujun9972][b]
|
||||
译者：[unigeorge](https://github.com/unigeorge)
|
||||
校对：[校对者ID](https://github.com/校对者ID)
|
||||
|
||||
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
|
||||
|
||||
[a]: https://opensource.com/users/seth
|
||||
[b]: https://github.com/lujun9972
|
||||
[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/lead-images/studying-books-java-couch-education.png?itok=C9gasCXr (Learning and studying technology is the key to success)
|
||||
[2]: https://opensource.com/article/21/8/linux-terminal#options
|
||||
[3]: https://opensource.com/article/19/7/what-posix-richard-stallman-explains
|
||||
[4]: https://commons.apache.org/proper/commons-cli/usage.html
|
||||
[5]: https://maven.apache.org/
|
||||
[6]: https://commons.apache.org/proper/commons-cli/download_cli.cgi
|
||||
[7]: http://www.google.com/search?hl=en&q=allinurl%3Adocs.oracle.com+javase+docs+api+string
|
||||
[8]: http://www.google.com/search?hl=en&q=allinurl%3Adocs.oracle.com+javase+docs+api+option
|
||||
[9]: http://www.google.com/search?hl=en&q=allinurl%3Adocs.oracle.com+javase+docs+api+system
|
||||
[10]: http://www.google.com/search?hl=en&q=allinurl%3Adocs.oracle.com+javase+docs+api+parseexception
|
||||
[11]: https://developers.redhat.com/blog/2021/04/08/build-even-faster-quarkus-applications-with-fast-jar
|
||||
Loading…
Reference in New Issue
Block a user