Class CallFilter

Input is sent as an XML request to given URI, and the output of this filter is the parsed response to that request. A connection is opened to the remote URI when the startDocument call is issued through this filter, and the request is finished when the endDocument call is issued. Events should be written quickly enough to prevent the remote HTTP server from aborting the connection due to inactivity; you may want to buffer text in an earlier pipeline stage. If your application requires validity checking of such outputs, have the output pipeline include a validation stage.

In effect, this makes a remote procedure call to the URI, with the request and response document syntax as chosen by the application. Note that all the input events must be seen, and sent to the URI, before the first output event can be seen. Clients are delayed at least by waiting for the server to respond, constraining concurrency. Services can thus be used to synchronize concurrent activities, and even to prioritize service among different clients.

You are advised to avoid restricting yourself to an "RPC" model for distributed computation. With a World Wide Web, network latencies and failures (e.g. non-availability) are significant; adopting a "procedure" model, rather than a workflow model where bulk requests are sent and worked on asynchronously, is not generally an optimal system-wide architecture. When the messages may need authentication, such as with an OpenPGP signature, or when server loads don't argue in favor of immediate responses, non-RPC models can be advantageous. (So-called "peer to peer" computing models are one additional type of model, though too often that term is applied to systems that still have a centralized control structure.)

Be strict in what you send, liberal in what you accept, as the Internet tradition goes. Strictly conformant data should never cause problems to its receiver; make your request pipeline be very strict, and don't compromise on that. Make your response pipeline strict as well, but be ready to tolerate specific mild, temporary, and well-documented variations from specific communications peers.

public CallFilter(String uri,
                  EventConsumer next)
            throws IOException

public final String getCallTarget()

public final ContentHandler getContentHandler()

public final DTDHandler getDTDHandler()

public final Object getProperty(String id)
            throws SAXNotRecognizedException

public final void setCallTarget(String uri)
            throws IOException

public void setErrorHandler(ErrorHandler handler)