用 JAVA 撸一遍 JVM 01: 命令行工具

第一章先通过main方法模拟cmd 输出一些相关信息

jcommander

引入依赖

<!-- 命令行参数解析器 -->
<dependency>
    <groupId>com.beust</groupId>
    <artifactId>jcommander</artifactId>
    <version>1.72</version>
</dependency>

Cmd

package com.linnine.jvm;

public class Cmd {

    @Parameter(names = {"-?", "-help"}, description = "print help message", order = 3, help = true)
    boolean helpFlag = false;

    @Parameter(names = "-version", description = "pringt version and exit", order = 2)
    boolean versionFlag = false;

    @Parameter(names = {"-cp", "-classpath"}, description = "classpath", order = 1)
    String classpath;

    @Parameter(description = "main class and args")
    List<String> mainClassAndArgs;

    boolean ok;

    String getMainClass() {
        return mainClassAndArgs != null && !mainClassAndArgs.isEmpty() ? mainClassAndArgs.get(0) : null;
    }

    List<String> getAppArgs() {
        return mainClassAndArgs != null && mainClassAndArgs.size() > 1 ? mainClassAndArgs.subList(1, mainClassAndArgs.size()) : null;
    }

    static Cmd parse(String[] argv) {
        Cmd args = new Cmd();
        JCommander cmd = JCommander.newBuilder().addCommand(args).build();
        cmd.parse(argv);
        args.ok = true;
        return args;
    }
}

main

package com.linnine.jvm;

public class Main {

    public static void main(String[] args) {
        Cmd cmd = Cmd.parse(args);
        if(!cmd.ok || cmd.helpFlag){
            System.out.println("Usage: <main class> [-options] class [args...]");
            return;
        }
        if (cmd.versionFlag){
            System.out.println("java version "1.8.0"");
            return;
        }
        startJvm(cmd);

    }

    private static void startJvm(Cmd cmd) {
        System.out.printf("classpath:%s class:%s args:%s
", cmd.classpath, cmd.getMainClass(), cmd.getAppArgs());
    }
}

报错了,挺懵逼的

人麻了 这里方法用错了,上面顺手打了个addCommand() 但还是有点问题 还是不太行 先跳过

我又跳回来了, 少了一些调试配置

idea上面的run , 这里加上参数-version, 原本是提示program arguments 然后就可以了