编写Java程序，实现一个简单的echo程序（网络编程TCP实践练习）

首先启动服务端，客户端通过TCP的三次握手与服务端建立连接；

然后，客户端发送一段字符串，服务端收到字符串后，原封不动的发回给客户端。

ECHO 程序是网络编程通信交互的一个经典案例，称为回应程序，即客户端输入哪些内容，服务端会在这些内容前加上“ECHO”并将信息发回给客户端。

EchoServer.java

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.net.ServerSocket;
import java.net.Socket;

public class EchoServer {
	private ServerSocket server;

	public EchoServer() throws IOException {
		// 创建服务端套接字对象
		this.server = new ServerSocket(8888);
		System.out.println("服务器启动" + "在" + 8888 + "端口监听连接请求");
	}

	// 服务器主要的处理逻辑
	public void service() {
		// 是否关闭服务端连接
		boolean flag = true;
		while (flag) {
			Socket socket = null;
			try {
				// 获取连接的客户端套接字对象
				socket = server.accept();
				// 获取socket相关的输入流和输出流
				BufferedReader reader = getReader(socket);
				BufferedWriter writer = getWriter(socket);
				// 保存客户端发送的数据
				String data = null;
				// 读取客户端发送的数据
				while ((data = reader.readLine()) != null) {
					// 当获取的信息是“bye”时，关闭流
					if ("bye".equals(data)) {
						flag = false;
						if (reader != null) {
							reader.close();
						}
						if (writer != null) {
							writer.close();
						}
						break;
					} else {
						System.out.println("来自客户端的数据：" + data);
						// 回显给客户端的数据
						writer.write("echo:" + data);
						// 插入一个行分割符，readLine()方法用来判定字符串有没结束
						writer.newLine();
						// 刷新输出缓冲区
						writer.flush();
					}
				}
			} catch (IOException e) {
				// 设置结束循环
				flag = false;
			} finally {
				try {
					if (server != null && (!server.isClosed())) {
						server.close();
						System.out.println("服务端关闭");
					}
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
		}
	}

	// 获取socket相关的输入流对象
	private BufferedReader getReader(Socket socket) throws IOException {
		InputStream in = socket.getInputStream();
		return new BufferedReader(new InputStreamReader(in));
	}

	// 获取socket相关的输出流对象
	private BufferedWriter getWriter(Socket socket) throws IOException {
		OutputStream out = socket.getOutputStream();
		return new BufferedWriter(new OutputStreamWriter(out));
	}

	public static void main(String arg[]) throws IOException {
		new EchoServer().service();
	}
}

EchoClient.java

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.net.Socket;

public class EchoClient {
	private Socket socket;

	public EchoClient() {
		try {
			// 创建客户端套接字对象
			this.socket = new Socket("127.0.0.1", 8888);
		} catch (IOException e) {
			e.printStackTrace();
		}
	}

	public void talkToServer() {
		System.out.println("请输入要发送给服务端的数据：");
		BufferedReader localReader = null;
		String data = null;
		// 获取客户端套接字相关的输入流和输出流
		BufferedReader reader = getReader(socket);
		BufferedWriter writer = getWriter(socket);
		try {
			// 创建读取用户输入的读取流
			localReader = new BufferedReader(new InputStreamReader(System.in));
			while ((data = localReader.readLine()) != null) {
				// 如果客户端输入的数据是"bye"，则关闭I/O流
				if ("bye".equals(data)) {
					System.out.println("客服端关闭!");
					if (reader != null) {
						reader.close();
					}
					if (writer != null) {
						writer.close();
					}
					break;
				} else {
					// readLine方法必须读取到行分割符才返回读取。所以传递给输入流的字符串必须包含行分割符
					System.out.println("客户端输出的数据--->\t" + data);
					writer.write(data);
					// 插入一个行分隔符,作为内容结束的标识
					writer.newLine();
					// 非常重要的是必须显式的将数据推送到服务器哪里去
					writer.flush();
					// 读取服务端返回的数据
					System.out.println("服务器响应的数据--->\t " + reader.readLine());
				}
			}
		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			// 关闭客户端套接字连接
			try {
				if (socket != null) {
					socket.close();
				}
			} catch (IOException e) {
				e.printStackTrace();
			}
		}
	}

	// 获取客户端套接字相关的输出流
	private BufferedWriter getWriter(Socket socket) {
		try {
			OutputStream out = null;
			BufferedWriter writer = null;
			out = socket.getOutputStream();
			writer = new BufferedWriter(new OutputStreamWriter(out));
			return writer;
		} catch (Exception e) {
			e.printStackTrace();
		}
		return null;
	}

	// 获取客户端套接字相关的输入流
	private BufferedReader getReader(Socket socket) {
		try {
			InputStream in = null;
			BufferedReader reader = null;
			in = socket.getInputStream();
			reader = new BufferedReader(new InputStreamReader(in));
			return reader;
		} catch (Exception e) {
			e.printStackTrace();
		}
		return null;
	}

	public static void main(String[] args) {
		new EchoClient().talkToServer();
	}
}