HttpAsyncClient 是一个异步的 HTTP 客户端开发包，基于 HttpCore NIO 和 HttpClient 组件。
HttpAsyncClient 的出现并不是为了替换 HttpClient，而是作为一个补充用于需要大量并发连接，对性能要求非常高的基于HTTP的原生数据通信，而且提供了事件驱动的 API。
改进日志如下：
* HttpCore upgraded to version 4.4.5
* HttpClient upgraded to version 4.5.2
* [HTTPASYNC-105] socketTimeout is not reset back to default after a request that has specific
timeout
Contributed by Oleg Kalnichevski
* [HTTPASYNC-101 CachingHttpAsyncClient to create default HttpContext if none specified
Contributed by Oleg Kalnichevski
* [HTTPASYNC-97] Upgraded HttpClient OSGi dependency to 4.5
Contributed by Oleg Kalnichevski
下载地址：http://hc.apache.org/downloads.cgi
来自:开源中国社区