用Java写个服务器和客户端，客户端传json给服务端，服务端读取数据传给客户

好的，这个可以使用Java的Socket编程实现。以下是一个简单的示例，仅供参考：

服务端代码：

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

public class Server {
    public static void main(String[] args) throws IOException {
        ServerSocket serverSocket = null;
        try {
            // 创建ServerSocket对象，指定监听的端口号
            serverSocket = new ServerSocket(8888);
        } catch (IOException e) {
            System.err.println("Could not listen on port: 8888.");
            System.exit(1);
        }

        Socket clientSocket = null;
        try {
            System.out.println("Waiting for connection...");
            // 等待客户端连接
            clientSocket = serverSocket.accept();
            System.out.println("Client connected: " + clientSocket);
        } catch (IOException e) {
            System.err.println("Accept failed.");
            System.exit(1);
        }

        // 获取输入输出流
        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("Received: " + inputLine);
            // 将接收到的数据发送回客户端
            out.println(inputLine);
        }

        // 关闭连接
        out.close();
        in.close();
        clientSocket.close();
        serverSocket.close();
    }
}

客户端代码：

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

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

        try {
            // 创建Socket对象，指定连接的服务器和端口号
            socket = new Socket("localhost", 8888);
            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);
        }

        // 构造JSON对象
        JSONObject json = new JSONObject();
        json.put("name", "张三");
        json.put("age", 18);

        // 向服务端发送JSON数据
        out.println(json.toString());

        // 接收服务端返回的数据
        String response = in.readLine();
        System.out.println("Response from server: " + response);

        // 关闭连接
        out.close();
        in.close();
        socket.close();
    }
}

注意：以上示例代码仅仅是一个简单的示例，实际使用时还需要处理异常、加入数据校验等等。此外，JSON的处理可以使用第三方库，比如Gson、Jackson等。