Executor將線程的創建和線程的執行解耦，比較下面兩個例子：

1：TaskExecutionWebServer.java

package chapter06;

import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.concurrent.Executor;
import java.util.concurrent.Executors;

public class TaskExecutionWebServer {
    private static final
 
 int NTHREADS=100;
    private static final Executor exec = Executors.newFixedThreadPool(NTHREADS);

    public static void main(String[] args) throws IOException {
        ServerSocket serverSocket = new ServerSocket(100);

        while (true) {
            final Socket connection=serverSocket.accept();
            Runnable task
 
=new Runnable() {  //Runnable 不處理異常，callable 處理異常。
                @Override
                public void run() {
                    //handlerRequest (connection);
                }
            };

            exec.execute(task);  //將Runnable 交給executor
        }
    }
}

2：ThreadPerTaskWebServer ,不可取。

package
 
 chapter06;

import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;

/**
 * @program: GradleTestUseSubModule
 * @author: Yafei Li
 * @create: 2018-07-13 21:05
 **/
public class ThreadPerTaskWebServer {
    public static void main(String[] args) throws IOException {
        ServerSocket socket = new ServerSocket(80);
        while (true) {
            final Socket connection=socket.accept();
            Runnable task=new Runnable() {
                @Override
                public void run() {
//                    handleRequest(connection);
                }
            };
            new Thread(task).start();
        }
    }
}

從上面兩個例子可以看出 Executors 會創建線程池，從線程池中取出線程執行任務。可以控制線程的數量。

而Thread要為每個任務創建一個線程，浪費資源。 開銷比較高。

所以Executors 能夠將創建線程與任務執行解耦， 控制線程數量等優點。

當遇到new Thread(Runnable).start(); 時，應該換為Executor.execute(Runnable);

Executor框架與Thread