如何使用Runtime.addShutdownHook

2019-11-18 15:29:47

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供稿：網(wǎng)友

以前從未用過 Runtime.addShutdownHook(Thread)，也不知道什么是 shutdown hook.
最近剛剛接觸了一點(diǎn)，總結(jié)一下。

根據(jù) java API, 所謂 shutdown hook 就是已經(jīng)初始化但尚未開始執(zhí)行的線程對(duì)象。在
Runtime 注冊(cè)后，假如 jvm 要停止前，這些 shutdown hook 便開始執(zhí)行。

有什么用呢？就是在你的程序結(jié)束前，執(zhí)行一些清理工作，尤其是沒有用戶界面的程序。

很明顯，這些 shutdown hook 都是些線程對(duì)象，因此，你的清理工作要寫在 run() 里。
根據(jù) Java API，你的清理工作不能太重了，要盡快結(jié)束。但仍然可以對(duì)數(shù)據(jù)庫進(jìn)行操作。

舉例如下：

package john2;
/**
* test shutdown hook
* All rights released and correctness not guaranteed.
*/
public class ShutdownHook implements Runnable {
public ShutdownHook() {
// register a shutdown hook for this class.
// a shutdown hook is an initialzed but not started thread, which will get up and run
// when the JVM is about to exit. this is used for short clean up tasks.
Runtime.getRuntime().addShutdownHook(new Thread(this));
System.out. }
// this method will be executed of course, since it's a Runnable.
// tasks should not be light and short, accessing database is alright though.
public void run() {
System.out.println("/n>>> About to execute: " + ShutdownHook.class.getName() + ".run() to clean up before JVM exits.");
this.cleanUp();
System.out.println(">>> Finished execution: " + ShutdownHook.class.getName() + ".run()");