org.directwebremoting.impl.PurgingDownloadManager Maven / Gradle / Ivy

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DWR is easy Ajax for Java. It makes it simple to call Java code directly from Javascript. It gets rid of almost all the boiler plate code between the web browser and your Java code.
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/*
 * 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.impl;

import java.io.IOException;
import java.util.concurrent.ScheduledThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

import javax.servlet.http.HttpServletRequest;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.directwebremoting.WebContextFactory;
import org.directwebremoting.extend.DownloadManager;
import org.directwebremoting.extend.FileGenerator;
import org.directwebremoting.util.IdGenerator;

/**
 * A {@link DownloadManager} that simply stores downloads in memory until they
 * are requested and then removes them.
 * @author Joe Walker [joe at getahead dot ltd dot uk]
 */
public abstract class PurgingDownloadManager implements DownloadManager
{
    /**
     * Schedule cache purges
     */
    public PurgingDownloadManager()
    {
        timer.scheduleWithFixedDelay(downloadPurge, queueSleepTime, queueSleepTime, TimeUnit.MILLISECONDS);
    }

    /* (non-Javadoc)
     * @see org.directwebremoting.extend.DownloadManager#addFile(org.directwebremoting.extend.DownloadManager.FileGenerator)
     */
    public String addFile(FileGenerator generator) throws IOException
    {
        String id = idGenerator.generateId(16);
        putFileGenerator(id, generator);

        HttpServletRequest request = WebContextFactory.get().getHttpServletRequest();
        return "'" + request.getContextPath() + request.getServletPath() + downloadHandlerUrl + id + "'";
    }

    /* (non-Javadoc)
     * @see org.directwebremoting.extend.DownloadManager#getFile(java.lang.String)
     */
    public FileGenerator getFile(String id)
    {
        return getFileGenerator(id);
    }

    /**
     * The URL part which we attach to the downloads.
     * @param downloadHandlerUrl The URL for this Handler.
     */
    public void setDownloadHandlerUrl(String downloadHandlerUrl)
    {
        this.downloadHandlerUrl = downloadHandlerUrl;
    }

    /**
     * @param purgeDownloadsAfter the purgeDownloadsAfter to set
     */
    public void setPurgeDownloadsAfter(long purgeDownloadsAfter)
    {
        this.purgeDownloadsAfter = purgeDownloadsAfter;
    }

    /**
     * Store a {@link FileGenerator} against a given id for
     * later retrieval.
     * @param id The id of the given FileGenerator
     * @param generator The FileGenerator to store against the id
     */
    protected abstract void putFileGenerator(String id, FileGenerator generator);

    /**
     * Retrieve a FileGenerator given the id that it was stored under
     * @param id The id to lookup
     * @return The matching FileGenerator or null if no match was found
     */
    protected abstract FileGenerator getFileGenerator(String id);

    /**
     * Remove all the stale entries from the cache
     */
    protected abstract void purge();

    /**
     * Loop over the known downloads removing the ones that are out of date
     */
    public class DownloadPurge implements Runnable
    {    
        /* (non-Javadoc)
         * @see java.lang.Runnable#run()
         */
        public void run()
        {
            purge();
        }
    }

    /**
     * The cron system
     */
    protected static ScheduledThreadPoolExecutor timer = new ScheduledThreadPoolExecutor(1);

    /**
     * Check that the cache of files does not contain out-of-date items
     */
    protected DownloadPurge downloadPurge = new DownloadPurge();

    /**
     * How often do we run purges on the data?
     */
    protected int queueSleepTime = 15000;

    /**
     * After some time we will give up waiting for a file to be downloaded.
     * By default this is 2 minutes. After this time we expect that the user
     * is no longer waiting and has gone away.
     */
    protected long purgeDownloadsAfter = 120000;

    /**
     * The URL part which we attach to the downloads.
     */
    protected String downloadHandlerUrl;

    /**
     * Unique id so we can retrieve downloads when asked
     */
    protected IdGenerator idGenerator = new IdGenerator();

    /**
     * The log stream
     */
    protected static final Log log = LogFactory.getLog(PurgingDownloadManager.class);
}