java Echo服务的客户端是如何实现的？

import java.io.BufferedReader; import java.io.DataInputStream; import java.io.DataOutputStream; import java.io.IOException; import java.io.InputStreamReader; import java.net.Socket; import java.net.UnknownHostException; public class EchoClient { public static void main(String args[]) { try { Socket connection = new Socket("", 7);// 创建Socket对象，Echo协议对应的端口为7号 System.out.println("已建立连接:"); DataInputStream in = new DataInputStream(connection .getInputStream());// 根据返回的Socket对象的输入流创建数据输入流 DataOutputStream out = new DataOutputStream(connection .getOutputStream());// 根据返回的Socket对象的输出流创建数据输出流 String line = new String(""); while (!line.toUpperCase().equals(".QUIT")) { System.out.println("输入字符串: "); line = EchoClient.readString();// 由键盘输入字符串 System.out.println("\t字符串发送到服务器 ..."); out.writeUTF(line);// 以UTF的编码形式将一个字符串写入数据输出流 System.out.println("\t等待服务器响应 ..."); line = in.readUTF();// 以UTF的编码形式从数据输入流中读字符串 System.out.println("Received: " + line);// 将读取的字符串显示出来 } in.close(); out.close(); connection.close(); } catch (UnknownHostException e) { System.err.println("Unknown host: " + args[0]); } catch (IOException e) { System.err.println(e.getMessage()); } } public static String readString() { String string = new String(); BufferedReader in = new BufferedReader(new InputStreamReader(System.in));// 创建一个可键盘录入的字符串缓冲区 try { string = in.readLine(); } catch (IOException e) { } return string; } }