Java Socket 多线程实例

概述

Java 网络编程的客户端和服务端编写都非常简单。客户端使用 Socket 对象与服务端交互；服务端创建 ServerSocket 对象，然后使用accept()方法进行监听，并返回一个Socket的对象。accept 方法是阻塞调用，并将一直阻塞，直到接收到下一个客户端请求为止。非多线程情况下，服务器同时只能服务一个客户端。这通常是不能满足现实需求的。

对于现实场景是通过在服务端创建多个线程来服务多个客户端，如下图：

服务端

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.SocketException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class EchoMultiServer {
    private static ServerSocket server = null;
    private static ExecutorService threadPool;

    public static void main(String[] args) {
        threadPool = Executors.newCachedThreadPool();
        threadPool.submit(new Monitor());

        try {
            server = new ServerSocket(10000);

            System.out.println("Server listening on port 10000 ....");
            System.out.println("Hit Enter to stop the server");

            while (true) {
                Socket socket = server.accept();
                System.out.println("Thread created");
                threadPool.submit(new EchoThread(socket));
            }
        } catch (SocketException e) {
            System.out.println("Server is down");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private static void shutdownServer() {
        try {
            server.close();
        } catch (IOException e) {
            e.printStackTrace();
        }

        threadPool.shutdown();
        System.exit(0);
    }

    private static class Monitor implements Runnable {

        @Override
        public void run() {
            try {
                while (System.in.read() != '\n') {}
            } catch (IOException e) {
            }

            shutdownServer();
        }
    }
}

class EchoThread implements Runnable {
    private Socket socket = null;
    private byte[] buffer = new byte[512];

    public EchoThread(Socket socket) {
        this.socket = socket;
    }

    @Override
    public void run() {
        try {
            InputStream is = socket.getInputStream();
            is.read(buffer);
            OutputStream os = socket.getOutputStream();
            os.write(buffer);
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                socket.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

客户端

import java.io.InputStream;
import java.io.OutputStream;
import java.net.InetSocketAddress;
import java.net.Socket;
import java.util.Scanner;

public class EchoMultiClient {
    private static int counter;

    public static void main(String[] args) {
        for (int i = 0; i < 100; i++) {
            counter++;
            new Thread(new Client(counter)).start();
        }
    }

    private static class Client implements Runnable {
        private int counter;

        public Client(int counter) {
            this.counter = counter;
        }

        @Override
        public void run() {
            try {
                Socket socket = new Socket();
                socket.connect(new InetSocketAddress("localhost", 10000), 1000);

                try {
                    OutputStream os = socket.getOutputStream();
                    String str = "Hello from Client " + counter;
                    os.write(str.getBytes());
                    InputStream is = socket.getInputStream();
                    Scanner scanner = new Scanner(is);
                    while (scanner.hasNextLine()) {
                        System.out.println(scanner.nextLine());
                    }

                    Thread.sleep(10);
                    scanner.close();
                } finally {
                    socket.close();
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
}