Java線程池

Java線程池表示一組正在等待作業並重複使用多次的工作線程。

線上程池的情況下，創建一組固定大小的線程。 來自線程池中的線程被拉出並由服務提供者分配作業。 完成作業後，線程再次包含線上程池中。

Java線程池的優點

提供了更好的性能，因為不需要重新創建新線程，所以節省了時間。

即時使用

在Servlet和JSP中使用，容器創建一個線程池來處理請求。

Java線程池的示例
下麵來看看使用ExecutorService和Executors的java線程池的簡單示例。

檔: WorkerThread.java

package com.zaixian;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

class WorkerThread implements Runnable {
    private String message;

    public WorkerThread(String s) {
        this.message = s;
    }

    public void run() {
        System.out.println(Thread.currentThread().getName() + " (Start) message = " + message);
        processmessage();// call processmessage method that sleeps the thread for 2 seconds
        System.out.println(Thread.currentThread().getName() + " (End)");// prints thread name
    }

    private void processmessage() {
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

檔: WorkerThread.java

package com.zaixian;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class TestThreadPool {
    public static void main(String[] args) {
       ExecutorService executor = Executors.newFixedThreadPool(5);//creating a pool of 5 threads
       for (int i = 0; i < 10; i++) {
           Runnable worker = new WorkerThread("" + i);
           executor.execute(worker);//calling execute method of ExecutorService
         }
       executor.shutdown();
       while (!executor.isTerminated()) {   }

       System.out.println("Finished all threads");
   }
}

執行上面示例代碼，得到以下結果：

pool-1-thread-2 (Start) message = 1
pool-1-thread-4 (Start) message = 3
pool-1-thread-5 (Start) message = 4
pool-1-thread-3 (Start) message = 2
pool-1-thread-1 (Start) message = 0
pool-1-thread-5 (End)
pool-1-thread-2 (End)
pool-1-thread-4 (End)
pool-1-thread-1 (End)
pool-1-thread-3 (End)
pool-1-thread-1 (Start) message = 6
pool-1-thread-3 (Start) message = 7
pool-1-thread-2 (Start) message = 5
pool-1-thread-4 (Start) message = 8
pool-1-thread-5 (Start) message = 9
pool-1-thread-3 (End)
pool-1-thread-5 (End)
pool-1-thread-4 (End)
pool-1-thread-1 (End)
pool-1-thread-2 (End)
Finished all threads