org.directwebremoting.servlet.DwrServlet 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.servlet;

import java.io.IOException;

import javax.servlet.ServletConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.commons.logging.LogFactory;
import org.apache.commons.logging.Log;
import org.directwebremoting.Container;
import org.directwebremoting.WebContextFactory.WebContextBuilder;
import org.directwebremoting.extend.ServerLoadMonitor;
import org.directwebremoting.impl.ContainerUtil;
import org.directwebremoting.impl.StartupUtil;

/**
 * This is the main servlet that handles all the requests to DWR.
 * It is on the large side because it can't use technologies like JSPs etc
 * since it all needs to be deployed in a single jar file, and while it might be
 * possible to integrate Velocity or similar I think simplicity is more
 * important, and there are only 2 real pages both script heavy in this servlet
 * anyway.
 * There are 5 things to do, in the order that you come across them:
 * 
 * The index test page that points at the classes
 * The class test page that lets you execute methods
 * The interface javascript that uses the engine to send requests
 * The engine javascript to form the iframe request and process replies
 * The exec 'page' that executes the method and returns data to the iframe
 * 
 * @author Joe Walker [joe at getahead dot ltd dot uk]
 * @noinspection RefusedBequest
 */
public class DwrServlet extends HttpServlet
{
    /* (non-Javadoc)
     * @see javax.servlet.GenericServlet#init(javax.servlet.ServletConfig)
     */
    @Override
    public void init(ServletConfig servletConfig) throws ServletException
    {
        super.init(servletConfig);
        ServletContext servletContext = servletConfig.getServletContext();

        try
        {
            // setupLogging() only needed for servlet logging if commons-logging is unavailable
            // logStartup() just outputs some version numbers
            StartupUtil.logStartup(servletConfig);

            // create and setup a DefaultContainer
            container = ContainerUtil.createAndSetupDefaultContainer(servletConfig);

            StartupUtil.initContainerBeans(servletConfig, servletContext, container);
            webContextBuilder = container.getBean(WebContextBuilder.class);

            ContainerUtil.prepareForWebContextFilter(servletContext, servletConfig, container, webContextBuilder, this);
            ContainerUtil.publishContainer(container, servletConfig);
            ContainerUtil.configureContainerFully(container, servletConfig);
        }
        catch (ExceptionInInitializerError ex)
        {
            log.fatal("ExceptionInInitializerError. Nested exception:", ex.getException());
            throw new ServletException(ex);
        }
        catch (Exception ex)
        {
            log.fatal("DwrServlet.init() failed", ex);
            throw new ServletException(ex);
        }
        finally
        {
            if (webContextBuilder != null)
            {
                webContextBuilder.unset();
            }
        }
    }

    /* (non-Javadoc)
     * @see javax.servlet.GenericServlet#destroy()
     */
    @Override
    public void destroy()
    {
        shutdown();
        super.destroy();
    }

    /**
     * Kill all comet polls.
     * Technically a servlet engine ought to call this only when all the
     * threads are already removed, however at least Tomcat doesn't do this
     * properly (it waits for a while and then calls destroy anyway).
     * It would be good if we could get {@link #destroy()} to call this
     * method however destroy() is only called once all threads are done so it's
     * too late.
     */
    public void shutdown()
    {
        ServerLoadMonitor monitor = container.getBean(ServerLoadMonitor.class);
        monitor.shutdown();
    }

    /* (non-Javadoc)
     * @see javax.servlet.http.HttpServlet#doGet(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse)
     */
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException, ServletException
    {
        doPost(req, resp);
    }

    /* (non-Javadoc)
     * @see javax.servlet.http.HttpServlet#doPost(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse)
     */
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException
    {
        try
        {
            webContextBuilder.set(request, response, getServletConfig(), getServletContext(), container);

            UrlProcessor processor = container.getBean(UrlProcessor.class);
            processor.handle(request, response);
        }
        finally
        {
            webContextBuilder.unset();
        }
    }

    /**
     * Accessor for the DWR IoC container.
     * @return DWR's IoC container
     */
    public Container getContainer()
    {
        return container;
    }

    /**
     * Our IoC container
     */
    private Container container = null;

    /**
     * The WebContext that keeps http objects local to a thread
     */
    private WebContextBuilder webContextBuilder = null;

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