“关闭钩子”(ShutdownHook)是这样一个概念:向虚拟机注册一个线程,当程序退出(Ctrl+C)时虚拟机会启动这个线程,我们可以在这个线程的run()中做一些清除的工作,如:释放数据库连接,关闭文件等.
注册:
Runtime.getRuntime().addShutdownHook(Thread t);
注销:
Runtime.getRuntime().removeShutdownHook(Thread t);
[例子]
/**
* 在这个线程中实现程序退出前的清理工作
*
* @author Administrator
*
*/
class TestThread extends Thread {
boolean isTerminal = false;
public void run() {
while (!isTerminal) {
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("run sub thread");
}
}
/**//**
* 清理工作
*/
public void onTerminal() {
isTerminal = true;
System.out.println("stop sun sub thread");
}
}
/**//**
* ShutdownDownHook测试类
*
* @author Administrator
*
*/
public class TestShutdownHook extends Thread {
TestThread testThread;
public void addThread(TestThread t) {
testThread = t;
}
/**//**
* 实现程序退出前的清理工作
*/
public void run() {
System.out.println("This is ShutdownHook");
testThread.onTerminal();
}
public static void main(String[] args) {
TestShutdownHook m = new TestShutdownHook();
TestThread t = new TestThread();
t.start();
m.addThread(t);
// 注册退出处理线程
Runtime.getRuntime().addShutdownHook(m);
}
}
运行结果:
run sub thread
run sub thread
run sub thread
run sub thread
This is ShutdownHook
stop sun sub thread
可以看到:当程序退出时启动了TestThread线程,执行了定义的释放工作。