ThreadGroup其实比ExecutorService更好(转)
??? 用java做抓取的时候免不了要用到多线程的了,因为要同时抓取多个网站或一条线程抓取一个网站的话实在太慢,而且有时一条线程抓取同一个网站的话也比较浪费CPU资源。要用到多线程的等方面,也就免不了对线程的控制或用到线程池。?? 我在做我们现在的那一个抓取框架的时候,就曾经用过java.util.concurrent.ExecutorService作为线程池,关于ExecutorService的使用代码大概如下:
java.util.concurrent.Executors类的API提供大量创建连接池的静态方法:1.固定大小的线程池:
1 package BackStage; 2 3 ?import java.util.concurrent.Executors; 4 ?import java.util.concurrent.ExecutorService; 5 6 ?public class JavaThreadPool { 7 public static void main(String[] args) { 8 // 创建一个可重用固定线程数的线程池 9 ? ExecutorService pool = Executors.newFixedThreadPool(2);10 // 创建实现了Runnable接口对象,Thread对象当然也实现了Runnable接口11 Thread t1 = new MyThread();12 Thread t2 = new MyThread();13 Thread t3 = new MyThread();14 Thread t4 = new MyThread();15 Thread t5 = new MyThread();16 // 将线程放入池中进行执行17 pool.execute(t1);18 pool.execute(t2);19 pool.execute(t3);20 pool.execute(t4);21 pool.execute(t5);22 // 关闭线程池23 pool.shutdown();24 }25 }26 27 class MyThread extends Thread {28 @Override29 public void run() {30 System.out.println(Thread.currentThread().getName() + "正在执行。。。");31 }32 }复制代码
?? 后来发现ExecutorService的功能没有想像中的那么好,而且最多只是提供一个线程的容器而然,所以后来我用改用了java.lang.ThreadGroup,ThreadGroup有很多优势,最重要的一点就是它可以对线程进行遍历,知道那些线程已经运行完毕,还有那些线程在运行。关于ThreadGroup的使用代码如下:
1 class MyThread extends Thread { 2 boolean stopped; 3 4 MyThread(ThreadGroup tg, String name) { 5 super(tg, name); 6 stopped = false; 7 } 8 9 public void run() {10 System.out.println(Thread.currentThread().getName() + " starting.");11 try {12 for (int i = 1; i < 1000; i++) {13 System.out.print(".");14 Thread.sleep(250);15 synchronized (this) {16 if (stopped)17 break;18 }19 }20 } catch (Exception exc) {21 System.out.println(Thread.currentThread().getName() + " interrupted.");22 }23 System.out.println(Thread.currentThread().getName() + " exiting.");24 }25 26 synchronized void myStop() {27 stopped = true;28 }29 }30 31 public class Main {32 public static void main(String args[]) throws Exception {33 ThreadGroup tg = new ThreadGroup("My Group");34 35 MyThread thrd = new MyThread(tg, "MyThread #1");36 MyThread thrd2 = new MyThread(tg, "MyThread #2");37 MyThread thrd3 = new MyThread(tg, "MyThread #3");38 39 thrd.start();40 thrd2.start();41 thrd3.start();42 43 Thread.sleep(1000);44 45 System.out.println(tg.activeCount() + " threads in thread group.");46 47 Thread thrds[] = new Thread[tg.activeCount()];48 tg.enumerate(thrds);49 for (Thread t : thrds)50 System.out.println(t.getName());51 52 thrd.myStop();53 54 Thread.sleep(1000);55 56 System.out.println(tg.activeCount() + " threads in tg.");57 tg.interrupt();58 }59 }复制代码
??由以上的代码可以看出:ThreadGroup比ExecutorService多以下几个优势??
1.ThreadGroup可以遍历线程,知道那些线程已经运行完毕,那些还在运行??
2.可以通过ThreadGroup.activeCount知道有多少线程从而可以控制插入的线程数
转自: http://www.cnblogs.com/jimmy0756/archive/2011/04/18/2019439.html