JVM 关闭钩子

package cn.edu.buaa.jvmhook;

/**
 * Runtime.getRuntime().addShutdownHook(shutdownHook);
 * <p>
 * 这个方法的意思就是在jvm中增加一个关闭的钩子，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。所以这些钩子可以在jvm关闭的时候进行内存清理、对象销毁等操作。
 * </p>
 * 用途１:应用程序正常退出，在退出时执行特定的业务逻辑，或者关闭资源等操作。
 */
public class JVMHook1 {

    public static void start() {
        System.out.println("The JVM is started");
        Runtime.getRuntime().addShutdownHook(new Thread() {
            public void run() {
                try {
                    // do something
                    System.out.println("The JVM Hook is execute");
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    public static void main(String[] args) {
        start();

        System.out.println("The Application is doing something");

        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        while (true) {
            ;
        }
    }
}


The JVM is started
The Application is doing something

package cn.edu.buaa.jvmhook;

/**
 * Runtime.getRuntime().addShutdownHook(shutdownHook);
 * <p>
 * 这个方法的意思就是在jvm中增加一个关闭的钩子，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。所以这些钩子可以在jvm关闭的时候进行内存清理、对象销毁等操作。
 * </p>
 * 用途２:虚拟机非正常退出，比如用户按下ctrl+c、OutofMemory宕机、操作系统关闭等。在退出时执行必要的挽救措施。
 */
public class JVMHook2 {
    public static void start() {
        System.out.println("The JVM is started");
        Runtime.getRuntime().addShutdownHook(new Thread() {
            public void run() {
                try {
                    // do something
                    System.out.println("The JVM Hook is execute");
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    public static void main(String[] args) {
        start();

        System.out.println("The Application is doing something");

        byte[] b = new byte[-1];

        System.out.println("The Application continues to do something");

        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}


The JVM is started
The Application is doing something
Exception in thread "main" java.lang.NegativeArraySizeException
    at cn.edu.buaa.jvmhook.JVMHook2.main(JVMHook2.java:31)
The JVM Hook is execute