HTTP 协议可能是现在 Internet 上使用得最多、最重要的协议了，越来越多的 Java 应用程序需要直接通过 HTTP 协议来访问网络资源。虽然在 JDK 的 java.net 包中已经提供了访问 HTTP 协议的基本功能，但是对于大部分应用程序来说，JDK 库本身提供的功能还不够丰富和灵活。
HttpURLConnection是java的标准类
HttpClient 是 Apache Jakarta Common 下的子项目，用来提供高效的、最新的、功能丰富的支持 HTTP 协议的客户端编程工具包，并且它支持 HTTP 协议最新的版本和建议。HttpClient 已经应用在很多的项目中，比如 Apache Jakarta 上很著名的另外两个开源项目 Cactus 和 HTMLUnit 都使用了 HttpClient，更多使用 HttpClient 的应用可以参见http://wiki.apache.org/jakarta-httpclient/HttpClientPowered。HttpClient 项目非常活跃，使用的人还是非常多的。目前 HttpClient 版本是在 2005.10.11 发布的 3.0 RC4 。
HttpClient是个很不错的开源框架，封装了访问http的请求头，参数，内容体，响应等等，
HttpURLConnection是java的标准类，什么都没封装，用起来太原始，不方便，比如重访问的自定义，以及一些高级功能等。
推荐HttpClient！！
URLConnection HTTPClient
Proxies and SOCKS Full support in Netscape browser, appletviewer, and applications (SOCKS: Version 4 only); no additional limitations from security policies.Full support (SOCKS: Version 4 and 5); limited in applets however by security policies; in Netscape can't pick up the settings from the browser.
Authorization Full support for Basic Authorization in Netscape (can use info given by the user for normal accesses outside of the applet); no support in appletviewer or applications.Full support everywhere; however cannot access previously given info from Netscape, thereby possibly requesting the user to enter info (s)he has already given for a previous access. Also, you can add/implement additional authentication mechanisms yourself.
Methods Only has GET and POST.Has HEAD, GET, POST, PUT, DELETE, TRACE and OPTIONS, plus any arbitrary method.
Headers Currently you can only set any request headers if you are doing a POST under Netscape; for GETs and the JDK you can't set any headers. Under Netscape 3.0 you can read headers only if the resource was returned with a Content-length header; if no Content-length header was returned, or under previous versions of Netscape, or using the JDK no headers can be read.Allows any arbitrary headers to be sent and received.
Automatic Redirection Handling Yes.Yes (as allowed by the HTTP/1.1 spec).
Persistent Connections No support currently in JDK; under Netscape uses HTTP/1.0 Keep-Alive's.Supports HTTP/1.0 Keep-Alive's and HTTP/1.1 persistence.
Pipelining of Requests No.Yes.
Can handle protocols other than HTTP Theoretically; however only http is currently implemented.No.
Can do HTTP over SSL (https) Under Netscape, yes. Using Appletviewer or in an application, no.No (not yet).
Source code available No.Yes.