用java语言写tcp通信的代码

下面是一个简单的Java TCP通信示例代码：

服务端代码：

import java.io.*;
import java.net.*;

public class TCPServer {
    public static void main(String[] args) throws IOException {
        ServerSocket serverSocket = null;
        try {
            serverSocket = new ServerSocket(9000);
        } catch (IOException e) {
            System.err.println("Could not listen on port: 9000.");
            System.exit(1);
        }

        Socket clientSocket = null;
        try {
            System.out.println("Waiting for connection.....");
            clientSocket = serverSocket.accept();
            System.out.println("Accepted connection from client: " + clientSocket.getInetAddress().getHostName());
        } catch (IOException e) {
            System.err.println("Accept failed.");
            System.exit(1);
        }

        PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);
        BufferedReader in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));

        String inputLine;

        while ((inputLine = in.readLine()) != null) {
            System.out.println("Server: " + inputLine);
            out.println(inputLine);

            if (inputLine.equals("Bye.")) {
                break;
            }
        }

        out.close();
        in.close();
        clientSocket.close();
        serverSocket.close();
    }
}

客户端代码：

import java.io.*;
import java.net.*;

public class TCPClient {
    public static void main(String[] args) throws IOException {
        Socket socket = null;
        PrintWriter out = null;
        BufferedReader in = null;

        try {
            socket = new Socket("localhost", 9000);
            out = new PrintWriter(socket.getOutputStream(), true);
            in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
        } catch (UnknownHostException e) {
            System.err.println("Don't know about host: localhost.");
            System.exit(1);
        } catch (IOException e) {
            System.err.println("Couldn't get I/O for the connection to: localhost.");
            System.exit(1);
        }

        BufferedReader stdIn = new BufferedReader(new InputStreamReader(System.in));
        String userInput;

        while ((userInput = stdIn.readLine()) != null) {
            out.println(userInput);

            String responseLine = in.readLine();
            System.out.println("Client: " + responseLine);

            if (responseLine.equals("Bye.")) {
                break;
            }
        }

        out.close();
        in.close();
        stdIn.close();
        socket.close();
    }
}

在这个例子中，服务端监听9000端口，等待客户端连接。客户端连接上服务端后，它可以从标准输入读取消息，并将其发送到服务端。服务端接收到消息后，将其打印到控制台上，并将其发送回客户端。客户端接收到响应后，也将其打印到控制台上。这个过程将一直持续，直到客户端发送`Bye.`消息，服务端将关闭连接。