pollhandler.java

来自「反向的AJAX。最大的特性是我们成为反向的Ajax。DWR1.x允许你用java」· Java 代码 · 共 445 行 · 第 1/2 页

/*
 * Copyright 2005 Joe Walker
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.directwebremoting.dwrp;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.directwebremoting.extend.ConverterManager;
import org.directwebremoting.extend.EnginePrivate;
import org.directwebremoting.extend.Handler;
import org.directwebremoting.extend.PageNormalizer;
import org.directwebremoting.extend.RealScriptSession;
import org.directwebremoting.extend.ScriptSessionManager;
import org.directwebremoting.extend.ServerException;
import org.directwebremoting.extend.ServerLoadMonitor;
import org.directwebremoting.util.Continuation;
import org.directwebremoting.util.MimeConstants;

/**
 * A Marshaller that output plain Javascript.
 * This marshaller can be tweaked to output Javascript in an HTML context.
 * This class works in concert with CallScriptConduit, they should be
 * considered closely related and it is important to understand what one does
 * while editing the other.
 * @author Joe Walker [joe at getahead dot ltd dot uk]
 */
public class PollHandler implements Handler
{
    /**
     * @param plain Are we using plain javascript or html wrapped javascript
     */
    public PollHandler(boolean plain)
    {
        this.plain = plain;
    }

    /* (non-Javadoc)
     * @see org.directwebremoting.Handler#handle(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse)
     */
    public void handle(HttpServletRequest request, HttpServletResponse response) throws IOException
    {
        // If you're new to understanding this file, you may wish to skip this
        // step and come back to it later ;-)
        // So Jetty does something a bit weird with Ajax Continuations. You
        // suspend a request (which works via an exception) while keeping hold
        // of a continuation object. There are methods on this continuation
        // object to restart the request. Also you can write to the output at
        // any time the request is suspended. When the continuation is
        // restarted, rather than restart the thread from where is was
        // suspended, it starts it from the beginning again. Since we are able
        // to write to the response outside of the servlet thread, there is no
        // need for us to do anything if we have been restarted. So we ignore
        // all Jetty continuation restarts.
        if (JettyContinuationSleeper.isRestart(request))
        {
            JettyContinuationSleeper.restart(request);
            return;
        }

        // A PollBatch is the information that we expect from the request.
        // if the parse fails we can do little more than tell the browser that
        // something went wrong.
        final PollBatch batch;
        try
        {
            batch = new PollBatch(request, pageNormalizer);
        }
        catch (ServerException ex)
        {
            // Send a batch exception to the server because the parse failed
            String script = EnginePrivate.getRemoteHandleBatchExceptionScript(null, ex);
            sendErrorScript(response, script);
            return;
        }

        String bodySessionId = batch.getHttpSessionId();
        checkNotCsrfAttack(request, bodySessionId);

        // We might need to complain that reverse ajax is not enabled.
        if (!activeReverseAjaxEnabled)
        {
            log.error("Polling and Comet are disabled. To enable them set the init-param activeReverseAjaxEnabled to true. See http://getahead.org/dwr/server/servlet for more.");
            String script = EnginePrivate.getRemotePollCometDisabledScript(batch.getBatchId());
            sendErrorScript(response, script);
            return;
        }

        // Complain if GET is disallowed
        if (batch.isGet() && !allowGetForSafariButMakeForgeryEasier)
        {
            // Send a batch exception to the server because the parse failed
            String script = EnginePrivate.getRemoteHandleBatchExceptionScript(batch.getBatchId(), new SecurityException("GET Disallowed"));
            sendErrorScript(response, script);
            return;
        }

        // A script conduit is some route from a ScriptSession back to the page
        // that belongs to the session. There may be zero or many of these
        // conduits (although if there are more than 2, something is strange)
        // All scripts destined for a page go to a ScriptSession and then out
        // via a ScriptConduit.
        final RealScriptSession scriptSession = batch.getScriptSession();

        // Create a conduit depending on the type of request (from the URL)
        final BaseScriptConduit conduit = createScriptConduit(batch, response);

        // So we're going to go to sleep. How do we wake up?
        final Sleeper sleeper;
        // If this is Jetty then we can use Continuations
        if (Continuation.isJetty())
        {
            sleeper = new JettyContinuationSleeper(request);
        }
        else
        {
            sleeper = new ThreadWaitSleeper();
        }

        // There are various reasons why we want to wake up and carry on ...
        final List alarms = new ArrayList();

        // If the conduit has an error flushing data, it needs to give up
        alarms.add(conduit.getErrorAlarm());

        // Set the system up to resume on output (perhaps with delay)
        if (batch.getPartialResponse() == PartialResponse.NO || maxWaitAfterWrite != -1)
        {
            // add an output listener to the script session that calls the
            // "wake me" method on whatever is putting us to sleep
            alarms.add(new OutputAlarm(scriptSession, maxWaitAfterWrite));
        }

        // Set the system up to resume anyway after maxConnectedTime
        long connectedTime = serverLoadMonitor.getConnectedTime();
        alarms.add(new TimedAlarm(connectedTime));

        // We also need to wake-up if the server is being shut down
        // WARNING: This code has a non-obvious side effect - The server load
        // monitor (which hands out shutdown messages) also monitors usage by
        // looking at the number of connected alarms.
        alarms.add(new ShutdownAlarm(serverLoadMonitor));

        // Make sure that all the alarms know what to wake
        for (Iterator it = alarms.iterator(); it.hasNext();)
        {
            Alarm alarm = (Alarm) it.next();
            alarm.setAlarmAction(sleeper);
        }

        // Register the conduit with a script session so messages can get out.
        // This must happen late on in this method because this will cause any
        // scripts cached in the script session (because there was no conduit
        // available when they were written) to be sent to the conduit.
        // We need any AlarmScriptConduits to be notified so they can make
        // maxWaitWfterWrite work for all cases
        scriptSession.addScriptConduit(conduit);

        // We need to do something sensible when we wake up ...
        Runnable onAwakening = new Runnable()
        {
            public void run()
            {
                // Cancel all the alarms
                for (Iterator it = alarms.iterator(); it.hasNext();)
                {
                    Alarm alarm = (Alarm) it.next();
                    alarm.cancel();
                }

                // We can't be used as a conduit to the browser any more
                scriptSession.removeScriptConduit(conduit);

                // Tell the browser to come back at the right time
                try
                {
                    int timeToNextPoll = serverLoadMonitor.getDisconnectedTime();
                    conduit.close(timeToNextPoll);
                }
                catch (IOException ex)
                {
                    log.warn("Failed to write reconnect info to browser");
                }
            }
        };

        // Actually go to sleep. This *must* be the last thing in this method to
        // cope with all the methods of affecting Threads. Jetty throws,
        // Weblogic continues, others wait().
        sleeper.goToSleep(onAwakening);
    }

    /**
     * Check that this request is not subject to a CSRF attack
     * @param request The original browser's request
     * @param bodySessionId The session id 
     */
    private void checkNotCsrfAttack(HttpServletRequest request, String bodySessionId)
    {
        // A check to see that this isn't a csrf attack
        // http://en.wikipedia.org/wiki/Cross-site_request_forgery
        // http://www.tux.org/~peterw/csrf.txt