欢迎使用Java Socket编程示例。
每个服务器都是在特定系统上运行并在特定端口上侦听的程序。
套接字绑定到端口号，当我们运行任何服务器时，它仅侦听套接字并等待客户端请求。
例如，运行在端口8080上的tomcat服务器等待客户端请求，一旦获得任何客户端请求，它就会响应它们。

Java套接字编程

套接字是网络上运行的两个程序之间双向通信链接的一个端点。
套接字绑定到一个端口号，以便TCP层可以识别应发送数据的应用程序。

在Java套接字编程示例教程中，我们将学习如何编写Java套接字服务器和Java套接字客户端程序。
我们还将学习服务器客户端程序如何在套接字上读写数据。

java.net.Socket和java.net.ServerSocket是实现Socket和Socket服务器的Java类。

Java套接字服务器示例

package com.theitroad.socket;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.lang.ClassNotFoundException;
import java.net.ServerSocket;
import java.net.Socket;

/**
 * This class implements java Socket server
 * @author hyman
 *
 */
public class SocketServerExample {
  
  //static ServerSocket variable
  private static ServerSocket server;
  //socket server port on which it will listen
  private static int port = 9876;
  
  public static void main(String args[]) throws IOException, ClassNotFoundException{
      //create the socket server object
      server = new ServerSocket(port);
      //keep listens indefinitely until receives 'exit' call or program terminates
      while(true){
          System.out.println("Waiting for the client request");
          //creating socket and waiting for client connection
          Socket socket = server.accept();
          //read from socket to ObjectInputStream object
          ObjectInputStream ois = new ObjectInputStream(socket.getInputStream());
          //convert ObjectInputStream object to String
          String message = (String) ois.readObject();
          System.out.println("Message Received: " + message);
          //create ObjectOutputStream object
          ObjectOutputStream oos = new ObjectOutputStream(socket.getOutputStream());
          //write object to Socket
          oos.writeObject("Hi Client "+message);
          //close resources
          ois.close();
          oos.close();
          socket.close();
          //terminate the server if client sends exit request
          if(message.equalsIgnoreCase("exit")) break;
      }
      System.out.println("Shutting down Socket server!!");
      //close the ServerSocket object
      server.close();
  }
  
}

Java套接字客户端

package com.theitroad.socket;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.InetAddress;
import java.net.Socket;
import java.net.UnknownHostException;

/**
 * This class implements java socket client
 * @author hyman
 *
 */
public class SocketClientExample {

  public static void main(String[] args) throws UnknownHostException, IOException, ClassNotFoundException, InterruptedException{
      //get the localhost IP address, if server is running on some other IP, you need to use that
      InetAddress host = InetAddress.getLocalHost();
      Socket socket = null;
      ObjectOutputStream oos = null;
      ObjectInputStream ois = null;
      for(int i=0; i<5;i++){
          //establish socket connection to server
          socket = new Socket(host.getHostName(), 9876);
          //write to socket using ObjectOutputStream
          oos = new ObjectOutputStream(socket.getOutputStream());
          System.out.println("Sending request to Socket Server");
          if(i==4)oos.writeObject("exit");
          else oos.writeObject(""+i);
          //read the server response message
          ois = new ObjectInputStream(socket.getInputStream());
          String message = (String) ois.readObject();
          System.out.println("Message: " + message);
          //close resources
          ois.close();
          oos.close();
          Thread.sleep(100);
      }
  }
}

为了测试服务器与客户端通信的Java套接字编程，首先我们需要运行SocketServerExample类。
当您运行套接字服务器时，它将仅显示" Waiting for client request"(等待客户端请求)，然后等待客户端请求。

现在，当您运行SocketClientExample类时，它将向Java套接字服务器发送请求，并将响应消息打印到控制台。

这是Java套接字服务器SocketServerExample程序的输出。

Waiting for the client request
Message Received: 0
Waiting for the client request
Message Received: 1
Waiting for the client request
Message Received: 2
Waiting for the client request
Message Received: 3
Waiting for the client request
Message Received: exit
Shutting down Socket server!!

这是Java套接字客户端SocketClientExample程序的输出。

Sending request to Socket Server
Message: Hi Client 0
Sending request to Socket Server
Message: Hi Client 1
Sending request to Socket Server
Message: Hi Client 2
Sending request to Socket Server
Message: Hi Client 3
Sending request to Socket Server
Message: Hi Client exit