Base class for org.apache.http.client.HttpClient implementations. This class acts as a facade to a number of special purpose handler or strategy implementations responsible for handling of a particular aspect of the HTTP protocol such as redirect or authentication handling or making decision about connection persistence and keep alive duration. This enables the users to selectively replace default implementation of those aspects with custom, application specific ones. This class also provides factory methods to instantiate those objects:

• HttpRequestExecutor object used to transmit messages over HTTP connections. The createRequestExecutor() must be implemented by concrete super classes to instantiate this object.
• BasicHttpProcessor object to manage a list of protocol interceptors and apply cross-cutting protocol logic to all incoming and outgoing HTTP messages. The createHttpProcessor() must be implemented by concrete super classes to instantiate this object.
• HttpRequestRetryHandler object used to decide whether or not a failed HTTP request is safe to retry automatically. The createHttpRequestRetryHandler() must be implemented by concrete super classes to instantiate this object.
• ClientConnectionManager object used to manage persistent HTTP connections.
• ConnectionReuseStrategy object used to decide whether or not a HTTP connection can be kept alive and re-used for subsequent HTTP requests. The createConnectionReuseStrategy() must be implemented by concrete super classes to instantiate this object.
• ConnectionKeepAliveStrategy object used to decide how long a persistent HTTP connection can be kept alive. The createConnectionKeepAliveStrategy() must be implemented by concrete super classes to instantiate this object.
• CookieSpecRegistry object used to maintain a list of supported cookie specifications. The createCookieSpecRegistry() must be implemented by concrete super classes to instantiate this object.
• CookieStore object used to maintain a collection of cookies. The createCookieStore() must be implemented by concrete super classes to instantiate this object.
• AuthSchemeRegistry object used to maintain a list of supported authentication schemes. The createAuthSchemeRegistry() must be implemented by concrete super classes to instantiate this object.
• CredentialsProvider object used to maintain a collection user credentials. The createCredentialsProvider() must be implemented by concrete super classes to instantiate this object.
• AuthenticationStrategy object used to authenticate against the target host. The createTargetAuthenticationStrategy() must be implemented by concrete super classes to instantiate this object.
• AuthenticationStrategy object used to authenticate against the proxy host. The createProxyAuthenticationStrategy() must be implemented by concrete super classes to instantiate this object.
• HttpRoutePlanner object used to calculate a route for establishing a connection to the target host. The route may involve multiple intermediate hops. The createHttpRoutePlanner() must be implemented by concrete super classes to instantiate this object.
• RedirectStrategy object used to determine if an HTTP request should be redirected to a new location in response to an HTTP response received from the target server.
• UserTokenHandler object used to determine if the execution context is user identity specific. The createUserTokenHandler() must be implemented by concrete super classes to instantiate this object.

This class also maintains a list of protocol interceptors intended for processing outgoing requests and incoming responses and provides methods for managing those interceptors. New protocol interceptors can be introduced to the protocol processor chain or removed from it if needed. Internally protocol interceptors are stored in a simple java.util.ArrayList. They are executed in the same natural order as they are added to the list.

AbstractHttpClient is thread safe. It is recommended that the same instance of this class is reused for multiple request executions. When an instance of DefaultHttpClient is no longer needed and is about to go out of scope the connection manager associated with it must be shut down by calling ClientConnectionManager#shutdown()!