[AndroidNet] HTTP API

Android includes two HTTP clients: HttpURLConnection and Apache HTTP Client. Both support HTTPS, streaming uploads and downloads, configurable timeouts, IPv6 and connection pooling.

• org.apache.http.impl.client.DefaultHttpClient - 主要使用 Apache 的 HttpClient
• Default implementation of an HTTP client.
• This class replaces HttpClient in HttpClient 3.

• android.net.http.AndroidHttpClient - API 8 - 主要使用 Apache 的 HttpClient
• Implementation of the Apache DefaultHttpClient that is configured with reasonable default settings and registered schemes for Android, and also lets the user add HttpRequestInterceptor classes. 
• Don't create this directly, use the newInstance(String) factory method.

Their implementation is stable and they have few bugs. But Android Team is not actively working on Apache HTTP Client.

• org.apache.http.client.httpClient - 做的事 就是 browser 送出 url 的那個動作
• Interface for an HTTP client. HTTP clients encapsulate a smorgasbord of objects required to execute HTTP requests while handling cookies, authentication, connection management, and other features. 
• Thread safety of HTTP clients depends on the implementation and configuration of the specific client.

• abstract java.net.URLConnection
• Instances of URLConnection are not reusable: you must use a different instance for each connection to a resource.
• An URLConnection for HTTP (RFC 2616) used to send and receive data over the web. Data may be of any type and length.

• java.net.HttpURLConnection extends URLConnection
• This class may be used to send and receive streaming data whose length is not known in advance.
• Is a general-purpose, lightweight HTTP client suitable for most applications.
• Prior to Froyo, HttpURLConnection had some frustrating bugs.
• Work around this by disabling connection pooling (Refer:  Android’s HTTP Clients | Android Developers Blog)
• In Gingerbread, we added transparent response compression.
• In Ice Cream Sandwich, we are adding a response cache.

• How to choose?
• Eclair and Froyo  - Apache HTTP client that has fewer bugs.
• For Gingerbread and better -  HttpURLConnection.
• Its simple API and small size makes it great fit for Android.
• Transparent compression and response caching reduce network use, improve speed and save battery.
• Android Team will be spending our energy going forward.

* Reference
- Android’s HTTP Clients | Android Developers Blog
- Android 上的 HTTP 服務相關函式 (I)
- Android 上的 HTTP 服務相關函式 (II)
- Android 上的 HTTP 服務相關函式 (III)