Quartz 的Web 应用-监听器方式调用

A ServletContextListner that can be used to initialize Quartz.

配置和集成 Quartz 到 Web 应用的一种方式。从 2.3 版本的 Servlet API 开始，能创建监听器，由容器在其生命周期中的某个特定时间回调。其中的一个监听器接口叫做 java.servlet.ServletContextListener，它包括有两个方法：

public void contextInitialized(ServletContextEvent sce);
public void contextDestroyed(ServeltContextEvent sce);

容器会在启动和关闭的时候相应的调用这两个方法。这就可以在 contextInitialized() 方法中初始化 Quartz Scheduler，并通过 contextDestroyed() 方法关闭它。
下面是QuartzInitializerListener 源码：

/**//*
 * Copyright 2004-2005 OpenSymphony
 *
 * 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.
 *
 */

/**//*
 * Previously Copyright (c) 2001-2004 James House
 */
package org.quartz.ee.servlet;

import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

import org.quartz.Scheduler;
import org.quartz.impl.StdSchedulerFactory;

/** *//**
 * <p>
 * A ServletContextListner that can be used to initialize Quartz.
 * </p>
 *
 * <p>
 * You'll want to add something like this to your WEB-INF/web.xml file:
 *
 * <pre>
 *     &lt;context-param&gt;
 *         &lt;param-name&gt;config-file&lt;/param-name&gt;
 *         &lt;param-value&gt;/some/path/my_quartz.properties&lt;/param-value&gt;
 *     &lt;/context-param&gt;
 *     &lt;context-param&gt;
 *         &lt;param-name&gt;shutdown-on-unload&lt;/param-name&gt;
 *         &lt;param-value&gt;true&lt;/param-value&gt;
 *     &lt;/context-param&gt;
 *     &lt;context-param&gt;
 *         &lt;param-name&gt;start-scheduler-on-load&lt;/param-name&gt;
 *         &lt;param-value&gt;true&lt;/param-value&gt;
 *     &lt;/context-param&gt;
 *     
 *     &lt;listener&gt;
 *         &lt;listener-class&gt;
 *             org.quartz.ee.servlet.QuartzInitializerListener
 *         &lt;/listener-class&gt;
 *     &lt;/listener&gt;
 * </pre>
 *
 * </p>
 * <p>
 * The init parameter 'config-file' can be used to specify the path (and
 * filename) of your Quartz properties file. If you leave out this parameter,
 * the default ("quartz.properties") will be used.
 * </p>
 *
 * <p>
 * The init parameter 'shutdown-on-unload' can be used to specify whether you
 * want scheduler.shutdown() called when the servlet is unloaded (usually when
 * the application server is being shutdown). Possible values are "true" or
 * "false". The default is "true".
 * </p>
 *
 * <p>
 * The init parameter 'start-scheduler-on-load' can be used to specify whether
 * you want the scheduler.start() method called when the servlet is first loaded.
 * If set to false, your application will need to call the start() method before
 * the scheduler begins to run and process jobs. Possible values are "true" or
 * "false". The default is "true", which means the scheduler is started.
 * </p>
 *
 * A StdSchedulerFactory instance is stored into the ServletContext. You can gain access
 * to the factory from a ServletContext instance like this:
 * <br>
 * <pre>
 * StdSchedulerFactory factory = (StdSchedulerFactory) ctx
 *                .getAttribute(QuartzInitializerListener.QUARTZ_FACTORY_KEY);</pre>
 * <p>
 * The init parameter 'servlet-context-factory-key' can be used to override the
 * name under which the StdSchedulerFactory is stored into the ServletContext, in 
 * which case you will want to use this name rather than 
 * <code>QuartzInitializerListener.QUARTZ_FACTORY_KEY</code> in the above example.
 * </p>
 *
 * <p>
 * The init parameter 'start-delay-seconds' can be used to specify the amount
 * of time to wait after initializing the scheduler before scheduler.start()
 * is called.
 * </p>
 *
 * Once you have the factory instance, you can retrieve the Scheduler instance by calling
 * <code>getScheduler()</code> on the factory.
 *
 * @author James House
 * @author Chuck Cavaness
 * @author John Petrocik
 */
public class QuartzInitializerListener implements ServletContextListener {

    public static final String QUARTZ_FACTORY_KEY = "org.quartz.impl.StdSchedulerFactory.KEY";

    private boolean performShutdown = true;

    private Scheduler scheduler = null;

    /**//*
     * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     *
     * Interface.
     *
     * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     */

    public void contextInitialized(ServletContextEvent sce) {

        System.out.println("Quartz Initializer Servlet loaded, initializing Scheduler");

        ServletContext servletContext = sce.getServletContext();
        StdSchedulerFactory factory;
        try {

            String configFile = servletContext.getInitParameter("config-file");
            String shutdownPref = servletContext.getInitParameter("shutdown-on-unload");

            if (shutdownPref != null) {
                performShutdown = Boolean.valueOf(shutdownPref).booleanValue();
            }

            // get Properties
            if (configFile != null) {
                factory = new StdSchedulerFactory(configFile);
            } else {
                factory = new StdSchedulerFactory();
            }

            // Always want to get the scheduler, even if it isn't starting, 
            // to make sure it is both initialized and registered.
            scheduler = factory.getScheduler();

            // Should the Scheduler being started now or later
            String startOnLoad = servletContext
                    .getInitParameter("start-scheduler-on-load");

            int startDelay = 0;
            String startDelayS = servletContext.getInitParameter("start-delay-seconds");
            try {
                if(startDelayS != null && startDelayS.trim().length() > 0)
                    startDelay = Integer.parseInt(startDelayS);
            } catch(Exception e) {
                System.out.println("Cannot parse value of 'start-delay-seconds' to an integer: " + startDelayS + ", defaulting to 5 seconds.");
                startDelay = 5;
            }

            /**//*
             * If the "start-scheduler-on-load" init-parameter is not specified,
             * the scheduler will be started. This is to maintain backwards
             * compatability.
             */
            if (startOnLoad == null || (Boolean.valueOf(startOnLoad).booleanValue())) {
                if(startDelay <= 0) {
                    // Start now
                    scheduler.start();
                    System.out.println("Scheduler has been started");
                }
                else {
                    // Start delayed
                    scheduler.startDelayed(startDelay);
                    System.out.println("Scheduler will start in " + startDelay + " seconds.");
                }
            } else {
                System.out.println("Scheduler has not been started. Use scheduler.start()");
            }

            String factoryKey = 
                servletContext.getInitParameter("servlet-context-factory-key");
            if (factoryKey == null) {
                factoryKey = QUARTZ_FACTORY_KEY;
            }

            System.out.println("Storing the Quartz Scheduler Factory in the servlet context at key: "
                    + factoryKey);
            servletContext.setAttribute(factoryKey, factory);

        } catch (Exception e) {
            System.out.println("Quartz Scheduler failed to initialize: " + e.toString());
            e.printStackTrace();
        }
    }

    public void contextDestroyed(ServletContextEvent sce) {

        if (!performShutdown) {
            return;
        }

        try {
            if (scheduler != null) {
                scheduler.shutdown();
            }
        } catch (Exception e) {
            System.out.println("Quartz Scheduler failed to shutdown cleanly: " + e.toString());
            e.printStackTrace();
        }

        System.out.println("Quartz Scheduler successful shutdown.");
    }


}