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jeremybenn |
/* CallFilter.java --
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Copyright (C) 1999,2000,2001 Free Software Foundation, Inc.
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This file is part of GNU Classpath.
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GNU Classpath is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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GNU Classpath is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with GNU Classpath; see the file COPYING. If not, write to the
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Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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02110-1301 USA.
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Linking this library statically or dynamically with other modules is
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making a combined work based on this library. Thus, the terms and
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conditions of the GNU General Public License cover the whole
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combination.
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As a special exception, the copyright holders of this library give you
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permission to link this library with independent modules to produce an
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executable, regardless of the license terms of these independent
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modules, and to copy and distribute the resulting executable under
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terms of your choice, provided that you also meet, for each linked
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independent module, the terms and conditions of the license of that
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module. An independent module is a module which is not derived from
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or based on this library. If you modify this library, you may extend
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this exception to your version of the library, but you are not
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obligated to do so. If you do not wish to do so, delete this
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exception statement from your version. */
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package gnu.xml.pipeline;
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import java.io.IOException;
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import java.io.OutputStreamWriter;
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import java.net.URL;
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import java.net.URLConnection;
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import java.io.Writer;
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import org.xml.sax.DTDHandler;
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import org.xml.sax.ErrorHandler;
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import org.xml.sax.InputSource;
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import org.xml.sax.SAXException;
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import org.xml.sax.SAXNotRecognizedException;
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import org.xml.sax.XMLReader;
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import org.xml.sax.helpers.XMLReaderFactory;
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import gnu.xml.util.Resolver;
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import gnu.xml.util.XMLWriter;
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/**
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* Input is sent as an XML request to given URI, and the output of this
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* filter is the parsed response to that request.
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* A connection is opened to the remote URI when the startDocument call is
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* issued through this filter, and the request is finished when the
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* endDocument call is issued. Events should be written quickly enough to
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* prevent the remote HTTP server from aborting the connection due to
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* inactivity; you may want to buffer text in an earlier pipeline stage.
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* If your application requires validity checking of such
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* outputs, have the output pipeline include a validation stage.
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*
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* <p>In effect, this makes a remote procedure call to the URI, with the
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* request and response document syntax as chosen by the application.
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* <em>Note that all the input events must be seen, and sent to the URI,
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* before the first output event can be seen. </em> Clients are delayed
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* at least by waiting for the server to respond, constraining concurrency.
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* Services can thus be used to synchronize concurrent activities, and
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* even to prioritize service among different clients.
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*
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* <p> You are advised to avoid restricting yourself to an "RPC" model
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* for distributed computation. With a World Wide Web, network latencies
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* and failures (e.g. non-availability)
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* are significant; adopting a "procedure" model, rather than a workflow
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* model where bulk requests are sent and worked on asynchronously, is not
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* generally an optimal system-wide architecture. When the messages may
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* need authentication, such as with an OpenPGP signature, or when server
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* loads don't argue in favor of immediate responses, non-RPC models can
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* be advantageous. (So-called "peer to peer" computing models are one
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* additional type of model, though too often that term is applied to
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* systems that still have a centralized control structure.)
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*
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* <p> <em>Be strict in what you send, liberal in what you accept,</em> as
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* the Internet tradition goes. Strictly conformant data should never cause
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* problems to its receiver; make your request pipeline be very strict, and
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* don't compromise on that. Make your response pipeline strict as well,
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* but be ready to tolerate specific mild, temporary, and well-documented
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* variations from specific communications peers.
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*
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* @see XmlServlet
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*
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* @author David Brownell
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*/
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final public class CallFilter implements EventConsumer
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{
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private Requestor req;
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private EventConsumer next;
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private URL target;
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private URLConnection conn;
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private ErrorHandler errHandler;
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/**
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* Initializes a call filter so that its inputs are sent to the
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* specified URI, and its outputs are sent to the next consumer
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* provided.
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*
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* @exception IOException if the URI isn't accepted as a URL
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*/
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// constructor used by PipelineFactory
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public CallFilter (String uri, EventConsumer next)
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throws IOException
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{
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this.next = next;
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req = new Requestor ();
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setCallTarget (uri);
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}
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/**
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* Assigns the URI of the call target to be used.
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* Does not affect calls currently being made.
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*/
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final public void setCallTarget (String uri)
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throws IOException
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{
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target = new URL (uri);
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}
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/**
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* Assigns the error handler to be used to present most fatal
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* errors.
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*/
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public void setErrorHandler (ErrorHandler handler)
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{
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req.setErrorHandler (handler);
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}
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/**
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* Returns the call target's URI.
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*/
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final public String getCallTarget ()
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{
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return target.toString ();
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}
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/** Returns the content handler currently in use. */
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final public org.xml.sax.ContentHandler getContentHandler ()
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{
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return req;
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}
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/** Returns the DTD handler currently in use. */
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final public DTDHandler getDTDHandler ()
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{
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return req;
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}
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/**
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* Returns the declaration or lexical handler currently in
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* use, or throws an exception for other properties.
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*/
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final public Object getProperty (String id)
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throws SAXNotRecognizedException
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{
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if (EventFilter.DECL_HANDLER.equals (id))
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return req;
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if (EventFilter.LEXICAL_HANDLER.equals (id))
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return req;
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throw new SAXNotRecognizedException (id);
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}
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// JDK 1.1 seems to need it to be done this way, sigh
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ErrorHandler getErrorHandler () { return errHandler; }
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//
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// Takes input and echoes to server as POST input.
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// Then sends the POST reply to the next pipeline element.
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//
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final class Requestor extends XMLWriter
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{
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Requestor ()
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{
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super ((Writer)null);
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}
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public synchronized void startDocument () throws SAXException
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{
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// Connect to remote object and set up to send it XML text
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try {
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if (conn != null)
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throw new IllegalStateException ("call is being made");
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conn = target.openConnection ();
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conn.setDoOutput (true);
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conn.setRequestProperty ("Content-Type",
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"application/xml;charset=UTF-8");
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setWriter (new OutputStreamWriter (
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conn.getOutputStream (),
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"UTF8"), "UTF-8");
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} catch (IOException e) {
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fatal ("can't write (POST) to URI: " + target, e);
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}
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// NOW base class can safely write that text!
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super.startDocument ();
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}
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public void endDocument () throws SAXException
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{
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//
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// Finish writing the request (for HTTP, a POST);
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// this closes the output stream.
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//
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super.endDocument ();
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//
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// Receive the response.
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// Produce events for the next stage.
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//
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InputSource source;
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XMLReader producer;
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String encoding;
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try {
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source = new InputSource (conn.getInputStream ());
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// FIXME if status is anything but success, report it!! It'd be good to
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// save the request data just in case we need to deal with a forward.
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encoding = Resolver.getEncoding (conn.getContentType ());
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if (encoding != null)
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source.setEncoding (encoding);
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producer = XMLReaderFactory.createXMLReader ();
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producer.setErrorHandler (getErrorHandler ());
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EventFilter.bind (producer, next);
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producer.parse (source);
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conn = null;
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} catch (IOException e) {
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fatal ("I/O Exception reading response, " + e.getMessage (), e);
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}
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}
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}
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}
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