说明：  　Http客户端程序已集成在Java语言中，可以通过URLConnection类调用。遗憾的是，由于SUN没有公布Http客户程序的源码，它实现的细节仍是一个谜。本文根据HTTP协议规范，用Java.net.Socket类实现一个HTTP协议客户端程序。
(Http client program has been integrated into the Java language, URLConnection can call category. Unfortunately, because Sun has not announced Http client source code, it achieved the details are still a mystery. According to the HTTP protocol specification. with the realization of a category Java.net.Socket HTTP client program.)