java中RunTime类的用途

最近公司准备使用spark做流式计算，把原来做过的东西拿出来整理一下，有以下内容

1、通过java调用shell脚本启动spark

2、在虚拟机退出时执行特定的方法即注册一个回调函数

 对于Runtime类的测试

 Every Java application has a single instance of class Runtime 
 that allows the application to interface with the environment in 
 which the application is running.
 每个java应用程序都有一个RunTime运行时环境的实例,该实例是单例的,它代表着正在运行的应用程序的环境
 
 The current runtime can be obtained from the getRuntime method.
 An application cannot create its own instance of this class
 当前的运行时环境可以通过getRuntime方法获取,一个运行时环境不能创建自己的运行时环境的实例

package com.lyzx.linux;

import java.io.IOException;
import java.util.concurrent.TimeUnit;

public class RunTimeTest {
	public static void main(String[] args) {

//		normalExit();
		unNormalExit();
	}
	
	/**
	 * 使用java调用shell脚本,
	 * //shell脚本内容如下:spark-submit --master spark://master:7077 --class com.lyzx.pi.M /root/package/Pi.jar $1
	 * 
	 * 使用这个命令来执行shell脚本,如果按照下面的方式就意味着如果spark任务执行1个小时，就要等待一个小时才能获的执行的结果
	 * 
	 * @throws IOException
	 * @throws InterruptedException 
	 */
	public static void execShell() throws IOException{
		Runtime r = Runtime.getRuntime();
		Process p = r.exec("./spark.sh 10000");
		try {
			int waitFor = p.waitFor();
			System.out.println("waitFor:"+waitFor);
		} catch (InterruptedException e){
			e.printStackTrace();
		}
	}
	
	/**
	 * 非正常情况下推出，依然执行回调函数
	 */
	public static void unNormalExit(){
		Thread t = new Thread(new Hook());
		Runtime.getRuntime().addShutdownHook(t);
		
		Thread t1 = new Thread(new Th(),"A1");
		Thread t2 = new Thread(new Th(),"B1");
		
		t1.start();
		
		//此时主线程奔溃,但是回调函数依然执行
		int i = 1/0;
		System.out.println("====");
		t2.start();
	}
	
	/**
	 * 添加虚拟机结束时的回调函数
	 * 从下面的例子中可以看出，当4个子线程执行完毕后在执行回调函数
	 */
	public static void normalExit(){
		Thread t = new Thread(new Hook());
		Runtime.getRuntime().addShutdownHook(t);
		
		Thread t1 = new Thread(new Th(),"A");
		Thread t2 = new Thread(new Th(),"B");
		Thread t3 = new Thread(new Th(),"C");
		Thread t4 = new Thread(new Th(),"D");
		
		t1.start();
		t2.start();
		t3.start();
		t4.start();
	}
}


class Hook implements Runnable{
	@Override
	public void run() {
		System.out.println("回调函数.....");
	}
}


class Th implements Runnable{
	@Override
	public void run() {
		for(int i=0;i<500;i++){
			try {
				TimeUnit.MILLISECONDS.sleep(3);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
			System.out.println(Thread.currentThread().getName()+":::"+i);
		}
	}
}