Selects the proxy server to use, if any, when connecting to the
network resource referenced by a URL. A proxy selector is a
concrete sub-class of this class and is registered by invoking the
setDefault method. The
currently registered proxy selector can be retrieved by calling
getDefault method.
When a proxy selector is registered, for instance, a subclass
of URLConnection class should call the select
method for each URL request so that the proxy selector can decide
if a direct, or proxied connection should be used. The select method returns an iterator over a collection with
the preferred connection approach.
If a connection cannot be established to a proxy (PROXY or
SOCKS) servers then the caller should call the proxy selector's
connectFailed method to notify the proxy
selector that the proxy server is unavailable.
The default proxy selector does enforce a set of System Properties related to proxy settings.