Runtime.addShutdownHook用法

一.Runtime.addShutdownHook理解

在看别人的代码时，发现其中有这个方法，便顺便梳理一下。

void java.lang.Runtime.addShutdownHook(Thread hook)

该方法用来在jvm中增加一个关闭的钩子。当程序正常退出,系统调用 System.exit方法或虚拟机被关闭时才会执行添加的shutdownHook线程。其中shutdownHook是一个已初始化但并不有启动的线程，当jvm关闭的时候，会执行系统中已经设置的所有通过方法addShutdownHook添加的钩子，当系统执行完这些钩子后，jvm才会关闭。所以可通过这些钩子在jvm关闭的时候进行内存清理、资源回收等工作。  

 

二.示例代码

 

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

		Thread shutdownHookOne = new Thread() {
			public void run() {
				System.out.println("shutdownHook one...");
			}
		};
		Runtime.getRuntime().addShutdownHook(shutdownHookOne);

		Runnable threadOne = new Runnable() {
			public void run() {
				try {
					Thread.sleep(1000);
				} catch (InterruptedException e) {
					e.printStackTrace();
				}
				System.out.println("thread one doing something...");
			}
		};

		Runnable threadTwo = new Thread() {
			public void run() {
				try {
					Thread.sleep(2000);
				} catch (InterruptedException e) {
					e.printStackTrace();
				}
				System.out.println("thread two doing something...");
			}
		};

		threadOne.run();
		threadTwo.run();
	}
}

  

输出如下：

 

thread one doing something...
thread two doing something...

shutdownHook one...