说明：  编写一个Java网络应用程序，该应用分服务器端程序和客户端程序两部分。服务器程序启动后，监听端口5678的请求；客户端程序启动后，向服务器端口5678发送请求。服务器不断接收客户机所写入的信息，并且服务器也会做出"Receive"为回应，告知客户机已接收到消息。要求：服务器程序采用多线程开发，允许多个客户端程序同时连接。客户机发送"End"字符串时，客户端程序退出
(Write a Java web application, the application sub-server-side program and client program in two parts. Server program started, listening port 5678 of the request client program starts, send a request to the server port 5678. Server, the client continued to receive the written information, and the server will also make a " Receive" In response to inform the client has received the message. Requirements: Multi-threaded server program development, allowing multiple simultaneous connections the client program. The client sends " End" string, the client program exit)