《自己手动实现java虚拟机》第一章

一、实现命令行工具

1.1 java命令行格式

java [-options] class [args]
java [-options] -jar jarfile [args]

javaw [-options] class [args]

javaw [-options] -jar jarfile [args]

java命令传递三组参数：选项、主类名（或者JAR文件名）和main()方法参数。选项由减号（–）开头。javaw命令和java命令几乎一样，唯一的差别在于，javaw命令不显示命令行窗口

1.2 go语言源码实现

package main

import (
	"flag"
	"fmt"
	"os"
)
type Cmd struct {
	helpFlag bool
	versionFlag bool
	cpOption string
	class string
	args []string
}
func parseCmd() *Cmd  {
	cmd := &Cmd{}
	flag.Usage = printUsage
	// flag.TypeVar(Type指针, flag名, 默认值, 帮助信息)
	flag.BoolVar(&cmd.helpFlag,"help",false,"print help message")
	flag.BoolVar(&cmd.helpFlag,"?",false,"print help message")
	flag.BoolVar(&cmd.versionFlag,"version",false,"print version message")
	flag.StringVar(&cmd.cpOption,"classpath","","classpath")
	flag.StringVar(&cmd.cpOption,"cp","","classpath")
	flag.Parse()
	args := flag.Args()
	if len(args) > 0 {
		cmd.class = args[0]
		cmd.args = args[1:]
	}
	return cmd
}

func printUsage()  {
	fmt.Printf("Usage: %s [-options] class [args...]\n", os.Args[0])
}

package main
import "fmt"
func main() {
	cmd := parseCmd()
	if cmd.versionFlag{
		fmt.Println("version 0.0.1")
	}else if cmd.helpFlag || cmd.class == "" {
		printUsage()
	}else{
		startJVM(cmd)
	}
}

func startJVM(cmd *Cmd)  {
	fmt.Printf("classpath:%s class:%s args:%v\n",cmd.cpOption, cmd.class, cmd.args)
}

1.3 测试?

通过 go install编译，在设置go的工作环境时，通过setx GOPATH E:\go\workplace设置会生效