写一个Java程序满足客户端和服务器互相发送和接收字符串，使用多线程

以下是一个使用多线程的Java程序示例，满足客户端和服务器之间互相发送和接收字符串需求：

// 服务器
import java.io.*;
import java.net.*;

public Server {
    public static void main(String[] args {
        try {
            ServerSocket serverSocket = ServerSocket(8080);
            System.out.println("服务器已启动，等待客户端连接...");

            while (true) {
                Socket clientSocket = serverSocket.accept();
                System.out.println("客户端连接成功！");

                ClientHandler clientHandler = new ClientHandler(clientSocket);
                clientHandler.start();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

class ClientHandler extends Thread {
    private Socket clientSocket;

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

    @Override
    public void run() {
        try {
            BufferedReader reader = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
            PrintWriter writer = new PrintWriter(clientSocket.getOutputStream(), true);

            String inputLine;
            while ((inputLine = reader.readLine()) != null) {
                System.out.println("接收到客户端消息：" + inputLine);
                writer.println("服务器已接收到消息：" + inputLine);
            }

            reader.close();
            writer.close();
            clientSocket.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

// 客户端
import java.io.*;
import java.net.*;

public class Client {
    public static void main(String[] args) {
        try {
            Socket socket = new Socket("localhost", 8080);
            System.out.println("已连接到服务器！");

            BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
            BufferedReader serverReader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            PrintWriter writer = new PrintWriter(socket.getOutputStream(), true);

            String inputLine;
            while ((inputLine = reader.readLine()) != null) {
                writer.println(inputLine);
                String response = serverReader.readLine();
                System.out.println("服务器响应：" + response);
            }

            reader.close();
            serverReader.close();
            writer.close();
            socket.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

以上代码中，服务器监听本地的8080端口，客户端连接到服务器的地址和端口。客户端发送输入的字符串到服务器，服务器接收到字符串后发送响应给客户端。这个过程在两个独立的线程中进行，分别处理客户端和服务器的输入输出。