Java Apache CLI 可选命令行参数不起作用

Question

尝试使用

Apache Commons Command Line Interface 1.3.1

从这里它对于必需的参数工作正常，但似乎删除了任何可选参数。有人能发现我下面的代码有问题吗？

import org.apache.commons.cli.CommandLine;
import org.apache.commons.cli.CommandLineParser;
import org.apache.commons.cli.DefaultParser;
import org.apache.commons.cli.Option;
import org.apache.commons.cli.Options;
import org.apache.commons.cli.ParseException;

public class TestCommandLine {

    public static void main(String[] args) {

        // *****  test with command line arguments -R myfirstarg -O mysecondarg  *****
        // *****  the second arg is not being captured                          *****

        System.out.println("Number of Arguments : " + args.length);

        String commandline = "";
        for (String arg : args) {
            commandline = commandline + (arg + " ");
        }
        commandline.trim();
        System.out.println("Command-line arguments: " + commandline);

        // create Options object
        Options options = new Options();
        options.addOption("R", true, "Enter this required argument");
        Option optionalargument = Option.builder("O")
                .optionalArg(true)   // if I change this line to .hasArg(true) it works, but then is not optional
                .desc("Enter this argument if you want to")
                .build();
        options.addOption(optionalargument);

        // initialize variables used with command line arguments
        String firstargument = null;
        String secondargument = null;


        CommandLineParser parser = new DefaultParser();
        try {
            // parse the command line arguments
            CommandLine cmd = parser.parse( options, args );

            firstargument = cmd.getOptionValue("R");
            secondargument = cmd.getOptionValue("O");

            if(cmd.hasOption("R")){
                if(firstargument == null){
                    System.out.println("Must provide the first argument  ...  exiting...");
                    System.exit(0);
                }
                else {
                    System.out.println("First argument is " + firstargument);
                }
            }
            if(cmd.hasOption("O")) {
                // optional argument
                if (secondargument == null){
                    System.out.println("Second argument is NULL");
                }
                else{
                    // should end up here if optional argument is provided, but it doesn't happen
                    System.out.println("Second argument is " + secondargument);
                }
            }

        }
        catch( ParseException exp ) {
            // oops, something went wrong
            System.err.println( "Parsing failed.  Reason: " + exp.getMessage() );
        }
    }

}

上述代码的输出是：

Number of Arguments : 4
Command-line arguments: -R myfirstarg -O mysecondarg 
First argument is myfirstarg
Second argument is NULL

为什么“mysecondarg”没有被捕获？ 如果我将 .optionalArg(true) 行更改为 .hasArg(true)，则捕获第二个参数，但整个想法是能够选择将第二个参数排除在外。

Answer 1

看来除了 hasOptionalArgs 之外，您还需要设置 numberOfArgs 才能正常工作。

Answer 2

还有另一个 parse() 方法，它采用第三个参数选项，称为 stopAtNonOption。

将 stopAtNonOption 设置为 false 会导致解析失败，并在到达未知参数时抛出异常。

我发现解析器在到达未知参数时停止解析。

Answer 3

Apache Command-CLI 过于冗长，导致误解和问题。您可以使用方便的包装纸：

<dependency>
    <groupId>com.github.bogdanovmn.cmdline</groupId>
    <artifactId>cmdline-app</artifactId>
    <version>3.0.0</version>
</dependency>

原始代码将如下所示（按您的预期工作）：

import com.github.bogdanovmn.cmdline.CmdLineAppBuilder;

public class TestCommandLine {
    public static void main(String[] args) throws Exception {
        new CmdLineAppBuilder(args)
            .withArg("R", "Enter this required argument").required()
            .withArg("O", "Enter this argument if you want to")
            .withEntryPoint(options -> {
                // The R arg is required, we shouldn't check it is specified
                System.out.println("First argument is " + options.get("R"));
                if (options.has("O")) {
                    String secondargument = options.get("O");
                    if (secondargument == null) {
                        // Will never go here
                        System.out.println("Second argument is NULL");
                    } else{
                        // should end up here if optional argument is provided
                        System.out.println("Second argument is " + secondargument);
                    }
                }
            })
        .build().run();
    }
}

如果命令行参数为“-R myfirstarg -O”，它将抛出运行时异常：

java.lang.RuntimeException: Missing argument for option: O

请参阅文档了解更多详细信息