利用java socket 服务端客户端采用多线程，主线程负责接收请求，由主线程启动5个工作线程，每个工作线程隔100-1000毫秒，从11个地区号中随机抽取一个，开始5001端口，显示返回地区名称，每个线程抽取10次，即客户端共发起50个请求

好的，这个问题其实是对之前提到的多线程和Socket的应用。下面是利用Java Socket实现服务端和客户端多线程之间的交互，实现上述要求的代码：

服务端代码：

import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;

public class Server {
    public static void main(String[] args) {
        ServerSocket serverSocket = null;
        try {
            serverSocket = new ServerSocket(5001);
            System.out.println("Server started");
            for (int i = 1; i <= 5; i++) {
                WorkerThread workerThread = new WorkerThread(i);
                workerThread.start();
            }
            while (true) {
                Socket socket = serverSocket.accept();
                System.out.println("New client connected");
                ClientHandler clientHandler = new ClientHandler(socket);
                clientHandler.start();
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (serverSocket != null) {
                try {
                    serverSocket.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

上述代码中，我们首先创建了一个ServerSocket对象，并且在端口5001上启动服务。然后我们启动了5个工作线程WorkerThread，并且每个线程随机从11个地区中抽取一个，并且显示返回地区名称。

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;
import java.util.Random;

public class ClientHandler extends Thread {
    final Socket socket;

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

    @Override
    public void run() {
        try {
            BufferedReader input = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            PrintWriter output = new PrintWriter(socket.getOutputStream(), true);
            String request = input.readLine();
            System.out.println("Received request: " + request);
            Random random = new Random();
            String[] areas = {"Beijing", "Shanghai", "Guangzhou", "Shenzhen", "Hangzhou", "Chengdu", "Chongqing", "Wuhan", "Nanjing", "Suzhou", "Tianjin"};
            for (int i = 1; i <= 10; i++) {
                int areaIndex = random.nextInt(11);
                int port = 5001 + i;
                String response = areas[areaIndex];
                Thread.sleep(random.nextInt(901) + 100);
                output.println(response);
                System.out.println("Sent response: " + response);
            }
            socket.close();
        } catch (IOException | InterruptedException e) {
            e.printStackTrace();
        }
    }
}

上述代码中，我们创建了一个ClientHandler类，继承自Thread类，并且重写了run()方法。在run()方法中，我们首先从客户端读取请求，然后随机从11个地区中抽取一个，并且显示返回地区名称。在发送每个响应之间，我们让线程随机休眠100到1000毫秒，模拟真实场景下的网络延迟。

客户端代码：

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;

public class Client {
    public static void main(String[] args) {
        try {
            Socket socket = new Socket("localhost", 5001);
            PrintWriter output = new PrintWriter(socket.getOutputStream(), true);
            BufferedReader input = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            for (int i = 1; i <= 50; i++) {
                String request = "Request " + i;
                output.println(request);
                System.out.println("Sent request: " + request);
                String response = input.readLine();
                System.out.println("Received response: " + response);
            }
            socket.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

上述代码中，我们创建了一个Socket对象，并且连接到了服务端的IP地址和端口号。然后我们向服务端发送50个请求，并且输出发送和接收的请求和响应。

注意：上述代码仅为示例代码，可能无法直接运行，需要根据具体情况进行调整和修改。