透明 Transparent connections through HTTP proxies.

透明语境：

5、7层模型中数据链路层：透明传输；

谈谈如何使用Netty开发实现高性能的RPC服务器 - Newland - 博客园 http://www.cnblogs.com/jietang/p/5615681.html

RPC（Remote Procedure Call Protocol）远程过程调用协议，它是一种通过网络，从远程计算机程序上请求服务，而不必了解底层网络技术的协议。说的再直白一点，就是客户端在不必知道调用细节的前提之下，调用远程计算机上运行的某个对象，使用起来就像调用本地的对象一样。目前典型的RPC实现框架有：Thrift（facebook开源）、Dubbo（alibaba开源）等等。RPC框架针对网络协议、网络I/O模型的封装是透明的，对于调用的客户端而言，它就认为自己在调用本地的一个对象。至于传输层上，运用的是TCP协议、UDP协议、亦或是HTTP协议，一概不关心。从网络I/O模型上来看，是基于select、poll、epoll方式、还是IOCP（I/O Completion Port）方式承载实现的，对于调用者而言也不用关心。

Apache HttpComponents – HttpComponents HttpClient Overview http://hc.apache.org/httpcomponents-client-5.0.x/index.html

Features

• Standards based, pure Java, implementation of HTTP versions 1.0 and 1.1
• Full implementation of all HTTP methods (GET, POST, PUT, DELETE, HEAD, OPTIONS, and TRACE) in an extensible OO framework.
• Supports encryption with HTTPS (HTTP over SSL) protocol.
• Transparent connections through HTTP proxies.
• Tunneled HTTPS connections through HTTP proxies, via the CONNECT method.
• Basic, Digest, NTLMv1, NTLMv2, NTLM2 Session, SNPNEGO, Kerberos authentication schemes.
• Plug-in mechanism for custom authentication schemes.
• Pluggable secure socket factories, making it easier to use third party solutions
• Connection management support for use in multi-threaded applications. Supports setting the maximum total connections as well as the maximum connections per host. Detects and closes stale connections.
• Automatic Cookie handling for reading Set-Cookie: headers from the server and sending them back out in a Cookie: header when appropriate.
• Plug-in mechanism for custom cookie policies.
• Request output streams to avoid buffering any content body by streaming directly to the socket to the server.
• Response input streams to efficiently read the response body by streaming directly from the socket to the server.
• Persistent connections using KeepAlive in HTTP/1.0 and persistance in HTTP/1.1
• Direct access to the response code and headers sent by the server.
• The ability to set connection timeouts.
• Support for HTTP/1.1 response caching.
• Source code is freely available under the Apache License.