用java做抓取的時候免不了要用到多線程的了，因為要同時抓取多個網(wǎng)站或一條線程抓取一個網(wǎng)站的話實在太慢，而且有時一條線程抓取同一個網(wǎng)站的話也比較浪費CPU資源。要用到多線程的等方面，也就免不了對線程的控制或用到線程池。?? 我在做我們現(xiàn)在的那一個抓取框架的時候，就曾經(jīng)用過java.util.concurrent.ExecutorService作為線程池，關(guān)于ExecutorService的使用代碼大概如下：
java.util.concurrent.Executors類的API提供大量創(chuàng)建連接池的靜態(tài)方法：1.固定大小的線程池：

package BackStage;import java.util.concurrent.Executors;import java.util.concurrent.ExecutorService;public class JavaThreadPool {public static void main(String[] args) {// 創(chuàng)建一個可重用固定線程數(shù)的線程池ExecutorService pool = Executors.newFixedThreadPool(2);// 創(chuàng)建實現(xiàn)了Runnable接口對象，Thread對象當然也實現(xiàn)了Runnable接口Thread t1 = new MyThread();Thread t2 = new MyThread();Thread t3 = new MyThread();Thread t4 = new MyThread();Thread t5 = new MyThread();// 將線程放入池中進行執(zhí)行 pool.execute(t1);pool.execute(t2);pool.execute(t3);pool.execute(t4);pool.execute(t5);// 關(guān)閉線程池 pool.shutdown();} }class MyThread extends Thread {@Overridepublic void run() {System.out.println(Thread.currentThread().getName() + "正在執(zhí)行。。。");} }

后來發(fā)現(xiàn)ExecutorService的功能沒有想像中的那么好，而且最多只是提供一個線程的容器而然，所以后來我用改用了java.lang.ThreadGroup，ThreadGroup有很多優(yōu)勢，最重要的一點就是它可以對線程進行遍歷，知道那些線程已經(jīng)運行完畢，還有那些線程在運行。關(guān)于ThreadGroup的使用代碼如下：

class MyThread extends Thread {boolean stopped;MyThread(ThreadGroup tg, String name) {super(tg, name);stopped = false;}public void run() {System.out.println(Thread.currentThread().getName() + " starting.");try {for (int i = 1; i < 1000; i++) {System.out.print(".");Thread.sleep(250);synchronized (this) {if (stopped)break;}}} catch (Exception exc) {System.out.println(Thread.currentThread().getName() + " interrupted.");}System.out.println(Thread.currentThread().getName() + " exiting.");}synchronized void myStop() {stopped = true;} }public class Main {public static void main(String args[]) throws Exception {ThreadGroup tg = new ThreadGroup("My Group");MyThread thrd = new MyThread(tg, "MyThread #1");MyThread thrd2 = new MyThread(tg, "MyThread #2");MyThread thrd3 = new MyThread(tg, "MyThread #3");thrd.start();thrd2.start();thrd3.start();Thread.sleep(1000);System.out.println(tg.activeCount() + " threads in thread group.");Thread thrds[] = new Thread[tg.activeCount()];tg.enumerate(thrds);for (Thread t : thrds)System.out.println(t.getName());thrd.myStop();Thread.sleep(1000);System.out.println(tg.activeCount() + " threads in tg.");tg.interrupt();} }

由以上的代碼可以看出：ThreadGroup比ExecutorService多以下幾個優(yōu)勢??

1.ThreadGroup可以遍歷線程，知道那些線程已經(jīng)運行完畢，那些還在運行??

2.可以通過ThreadGroup.activeCount知道有多少線程從而可以控制插入的線程數(shù)

轉(zhuǎn)載于:https://www.cnblogs.com/onlywujun/p/3514564.html

總結(jié)

以上是生活随笔為你收集整理的ThreadGroup其实比ExecutorService更好的全部內(nèi)容，希望文章能夠幫你解決所遇到的問題。

如果覺得生活随笔網(wǎng)站內(nèi)容還不錯，歡迎將生活随笔推薦給好友。