The HttpCore components implement the most fundamental aspects of the HTTP
protocol. They are nonetheless sufficient to develop basic client-side and
server-side HTTP services with a minimal footprint and no external
dependencies.

The HttpCore base module contains the public API and the default
implementation based on the Java classic (blocking) I/O model. It requires
a Java 1.3 compatible runtime and has no dependency on any external libraries.

HttpCore NIO extensions contain optional components that leverage the event
driven, non-blocking I/O (NIO) model. HttpCore NIO extensions require a
Java 5.0 compatible runtime and the HttpCore base module. HttpCore NIO
extensions are intended for those usage scenarios where raw throughput is
less important than the ability to handle thousands of simultaneous HTTP
connections in a resource efficient manner.

WWW: http://hc.apache.org/httpcomponents-core/