21.获取进程

用字符串写一段伪代码,然后写入一个java文件,再调用进程编译

//调用javac进程
Process p = Runtime.getRuntime().exec("javac Hello.java");

//调用java进程
Process p1 = Runtime.getRuntime().exec("java Hello");

示例代码

package com.java520.iodemo01;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.OutputStream;




public class PersonDemo 
{
    public static void main(String[] args) throws Exception 
    {
        //写文件
        writeFile();
        
        //获取进程并运行
        getProcess();
    }

    private static void getProcess() throws Exception {
        // TODO Auto-generated method stub
        //1.调用javac 进程来编译Hello.java
        Process p = Runtime.getRuntime().exec("javac Hello.java");
        
        //2.有可能编译出错,所以需要获取一下编译后的流来得知编译信息
        InputStream errorStream = p.getErrorStream();
        
        byte[] b = new byte[1024];
        int ln = -1;
        while ((ln = errorStream.read(b)) != -1){
            String str = new String(b,0,ln);
            System.out.println(str);
        }
        //3.关闭资源
        errorStream.close();
        
        //4.调用java进程来编译Hello.class
        Process pjava = Runtime.getRuntime().exec("java Hello");
        
        //5.获取java进程中的的流信息
        InputStream infoStream = pjava.getInputStream();
        byte[] bjava = new byte[1024];
        int ln1 = -1;
        while((ln1 = infoStream.read(bjava)) != -1){
            String str = new String(bjava,0,ln1);
            System.out.println(str);
        }
        
        //6.关闭资源
        infoStream.close();
        
        //7.删除文件 
        new File("Hello.java").delete();
        new File("Hello.class").delete();
    }

    private static void writeFile() throws Exception{
        // TODO Auto-generated method stub
        StringBuilder str = new StringBuilder();

        str.append("public class Hello{");
        str.append("public static void main(String[] args){");
        str.append("System.out.println(\"你是我天边最美的云彩\");");
        str.append("}");
        str.append("}");

        //创建输出对象
        File file = new File("Hello.java");

        //创建输出流
        OutputStream out = new FileOutputStream(file);

        //输出
        out.write(str.toString().getBytes());
        
        //关闭
        out.close();
    }
}