java代码实现socket做服务端接收报文，并返回响应报文

可以使用以下代码实现socket做服务端接收报文，并返回响应报文：

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

public class Server {
    public static void main(String[] args) throws IOException {
        ServerSocket serverSocket = new ServerSocket(12345);
        System.out.println("Server started.");

        while (true) {
            Socket socket = serverSocket.accept();
            System.out.println("Client connected: " + socket.getInetAddress().getHostAddress());

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

            String inputLine;
            while ((inputLine = in.readLine()) != null) {
                System.out.println("Received message: " + inputLine);
                out.println("Response message: " + inputLine);
            }

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

这段代码会监听12345端口，当有客户端连接时，会打印客户端的IP地址。然后会读取客户端发送的消息，并返回相同的消息。当客户端关闭连接时，服务端也会关闭连接。