网络请求

2.2连接池关闭后失效

API简单，体积较小。压缩和缓存机制可以有效地减少网络访问的流量

2.3消息头加入gzip，客户端响应压缩

2.3 使用SNI(Server Name Indication)的方式进行连接

2.3压缩会话机制

4.0缓存机制

2.2版本之前，HttpClient拥有较少的bug，因此使用它是最好的选择

▪ 100 Continue ▪ 101 Switching Protocols ▪ 102 Processing

▪ 200 OK ▪ 201 Created ▪ 202 Accepted ▪ 203 Non-Authoritative Information ▪ 204 No Content ▪ 205 Reset Content ▪ 206 Partial Content ▪ 207 Multi-Status

▪ 300 Multiple Choices ▪ 301 Moved Permanently ▪ 302 Move temporarily ▪ 303 See Other ▪ 304 Not Modified ▪ 305 Use Proxy ▪ 306 Switch Proxy ▪ 307 Temporary Redirect

▪ 400 Bad Request ▪ 401 Unauthorized ▪ 402 Payment Required ▪ 403 Forbidden ▪ 404 Not Found ▪ 405 Method Not Allowed ▪ 406 Not Acceptable ▪ 407 Proxy Authentication Required ▪ 408 Request Timeout ▪ 409 Conflict ▪ 410 Gone ▪ 411 Length Required ▪ 412 Precondition Failed ▪ 413 Request Entity Too Large ▪ 414 Request-URI Too Long ▪ 415 Unsupported Media Type ▪ 416 Requested Range Not Satisfiable ▪ 417 Expectation Failed ▪ 421There are too many connections from your internet address ▪ 422 Unprocessable Entity ▪ 423 Locked ▪ 424 Failed Dependency ▪ 425 Unordered Collection ▪ 426 Upgrade Required ▪ 449 Retry With

▪ 500 Internal Server Error ▪ 501 Not Implemented ▪ 502 Bad Gateway ▪ 503 Service Unavailable ▪ 504 Gateway Timeout ▪ 505 HTTP Version Not Supported ▪ 506 Variant Also Negotiates ▪ 507 Insufficient Storage ▪ 509 Bandwidth Limit Exceeded ▪ 510 Not Extended ▪ 600 Unparseable Response Headers