用socket通讯写出客户端和服务器端的通讯，要求客户发送数据后能够回显相同的数据。

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

class Server {
	public Server() {
		BufferedReader br = null;
		PrintWriter pw = null;
		try {
			ServerSocket server = new ServerSocket(8888);// 建立服务器端
			Socket socket = server.accept();// 监听客户端
			// 得到该连接的输入流
			br = new BufferedReader(new InputStreamReader(socket
					.getInputStream()));
			// 得到该连接的输出流
			pw = new PrintWriter(socket.getOutputStream(), true);
			// 先读后写
			String data = br.readLine();
			System.out.println(data);// 输出到控制台
			pw.println(data);// 转发给客户端
		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			try {
				// 关闭读写流
				br.close();
				pw.close();
			} catch (Exception e) {
			}
		}
	}

	public static void main(String[] args) {
		Server server = new Server();
	}
}

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

class Client {
	public Client() {
		BufferedReader br = null;
		PrintWriter pw = null;
		try {
			Socket socket = new Socket("localhost", 8888);// 与服务器建立连接，服务器要先启
			// 得到Socket的输入与输出流
			br = new BufferedReader(new InputStreamReader(socket
					.getInputStream()));
			pw = new PrintWriter(socket.getOutputStream(), true);
			// 先写后读
			pw.println("Client:你好！");
			String data = null;
			while (true) {
				data = br.readLine();
				if (data != null)
					break;
			}
			System.out.println(data);
		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			try {
				br.close();
				pw.close();
			} catch (Exception e) {
			}
		}
	}

	public static void main(String[] args) {
		Client c = new Client();
	}
}