Quartz是一款定時任務調度的開源框架，使用起來比較方便。並且Spring的support包對Quartz有集成。但是筆者在web應用使用的過程中卻遇到了內存洩漏的問題。
問題的產生
筆者在使用Spring+Quartz的用法如下（熟悉Spring+Quartz的可以跳過直接看問題）：
1.配置Scheduler工廠
<bean id="schedulerFactory" class="org.springframework.scheduling.quartz.SchedulerFactoryBean">
</bean>
2.編寫Job的實現類QuartzJob，用來執行任務
//這裡須繼承spring的QuartzJobBean
public class QuartzJob extends QuartzJobBean {/**
* 任務執行內容。
*/
@Override
protected void executeInternal(JobExecutionContext context) throws JobExecutionException {
// 執行任務的代碼
}
}
3.將Scheduler工廠生產的scheduler注入到業務邏輯類中。這裡注意，注入的其實是由schedulerFactory生產出來的scheduler實例（對Spring不熟悉的人會自然而然的認為注入的是schedulerFactory的實例，這是因為Spring的SchedulerFactoryBean實現了FactoryBean接口，所以注入的結果會是FactoryBean.getObject()獲得的實例，題外話）。
<bean id="taskService" class="com.xxxx.xx.service.impl.TaskServiceImpl" init-method="init" scope="singleton">
<property name="scheduler">
<ref bean="schedulerFactory"/>
</property>
</bean>
public class TaskServiceImpl {
private Scheduler scheduler;/**
* 由spring通過工廠注入，此實例為單例。
* @param scheduler
*/
public void setScheduler(Scheduler scheduler) {
this.scheduler = scheduler;
}
4.在業務邏輯類TaskServiceImpl中，使用scheduler執行任務。這裡可以動態對任務執行增加、刪除、重啟等等操作。還有一個重要的特性是可以動態的改變Cron表達式，對任務的定時規則進行更改。
1 /**
2 * 新增任務。
3 * @param jobName
4 * @param jobGroup
5 * @param cron
6 */
7 public void addJob(String jobName, String jobGroup, String cron, String kindId) {
8 try {
9 if (StringUtil.isEmpty(jobName) || StringUtil.isEmpty(jobGroup) || StringUtil.isEmpty(cron)) {
10 throw new BusinessException("定時任務創建失敗，參數為空");
11 }
12 JobDetail jobDetail = JobBuilder.newJob(QuartzJob.class).withIdentity(jobName, jobGroup).build();
13 jobDetail.getJobDataMap().put("JobKind", kindId);
14 //表達式調度構建器
15 CronScheduleBuilder scheduleBuilder = CronScheduleBuilder.cronSchedule(cron);
16 //按新的cronExpression表達式構建一個新的trigger
17 CronTrigger trigger = TriggerBuilder.newTrigger().withIdentity(jobName, jobGroup).withSchedule(scheduleBuilder).build();
18 scheduler.scheduleJob(jobDetail, trigger);
19 log.info("新增定時任務，name:" + jobName + ",group:" + jobGroup + ",cron:" + cron);
20 } catch (SchedulerException e) {
21 // 對異常的處理
22 }
23 }
注意18行的scheduler是由Spring注入的。
這種用法在使用過程中沒有問題，但在web應用在Tomcat6中熱部署時出險了以下嚴重警告，如果忽略這種警告，在頻繁的reload後會造成Tomcat 的 Permgen space OOM。
Jun 24, 2014 5:14:38 AM org.apache.catalina.loader.WebappClassLoader clearReferencesThreads
SEVERE: The web application [/feeder##1.5.0] appears to have started a thread named [scheduler_Worker-1] but has failed to stop it. This is very likely to create a memory leak.
Jun 24, 2014 5:14:38 AM org.apache.catalina.loader.WebappClassLoader clearReferencesThreads
SEVERE: The web application [/feeder##1.5.0] appears to have started a thread named [scheduler_Worker-2] but has failed to stop it. This is very likely to create a memory leak.
Jun 24, 2014 5:14:38 AM org.apache.catalina.loader.WebappClassLoader clearReferencesThreads
SEVERE: The web application [/feeder##1.5.0] appears to have started a thread named [scheduler_Worker-3] but has failed to stop it. This is very likely to create a memory leak.
Jun 24, 2014 5:14:38 AM org.apache.catalina.loader.WebappClassLoader clearReferencesThreads
SEVERE: The web application [/feeder##1.5.0] appears to have started a thread named [scheduler_Worker-4] but has failed to stop it. This is very likely to create a memory leak.
Jun 24, 2014 5:14:38 AM org.apache.catalina.loader.WebappClassLoader clearReferencesThreads
SEVERE: The web application [/feeder##1.5.0] appears to have started a thread named [scheduler_Worker-5] but has failed to stop it. This is very likely to create a memory leak.
Jun 24, 2014 5:14:38 AM org.apache.catalina.loader.WebappClassLoader clearReferencesThreads
SEVERE: The web application [/feeder##1.5.0] appears to have started a thread named [scheduler_Worker-6] but has failed to stop it. This is very likely to create a memory leak.
Jun 24, 2014 5:14:38 AM org.apache.catalina.loader.WebappClassLoader clearReferencesThreads
問題的原因
究其原因是開啟的scheduler_Worker線程沒有關閉。但Spring的SchedulerFactoryBean實現了DisposableBean接口，表示web容器關閉時會執行destroy()，執行內容如下：
/**
* Shut down the Quartz scheduler on bean factory shutdown,
* stopping all scheduled jobs.
*/
public void destroy() throws SchedulerException {
logger.info("Shutting down Quartz Scheduler");
this.scheduler.shutdown(this.waitForJobsToCompleteOnShutdown);
}
表示工廠已經做了shutdown。所以，問題出現在真正執行的scheduler.shutdown(true)。
原來這是Quartz的bug(見https://jira.terracotta.org/jira/browse/QTZ-192)，在調用scheduler.shutdown(true)後，Quartz檢查線程並沒有等待那些worker線程被停止就結束了。
網上說在Quartz2.1版本已經修補了這個bug，但筆者使用的2.2.1版本仍舊有問題。
問題的解決
那麼問題如何解決，這裡有一個不太美觀的方案：在調用scheduler.shutdown(true)後，增加一點睡眠時間，等待worker線程全部停止。如下：
1。自定義schedulerFactory繼承Spring的SchedulerFactoryBean，覆蓋destroy()增加延時。
public class SchedulerFactoryBeanWithShutdownDelay extends SchedulerFactoryBean {
/**
* 關於Quartz內存洩漏的不太美觀的解決方案：
* 在調用scheduler.shutdown(true)後增加延時，等待worker線程結束。
*/
@Override
public void destroy() throws SchedulerException {
super.destroy();
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
throw new RuntimeException(e);
}
}
}
2。把spring配置文件中的SchedulerFactoryBean替換為自定義的工廠即可。
<bean id="schedulerFactory" class="com.sinosoft.ms.task.SchedulerFactoryBeanWithShutdownDelay">
</bean>
OK，問題解決。
Spring配置Quartz任務調度框架教程 http://www.linuxidc.com/Linux/2014-11/108907.htm
Quartz深入淺出 http://www.linuxidc.com/Linux/2014-09/107007.htm
Quartz1.6有狀態JOB碰到的棘手問題既解決方案 http://www.linuxidc.com/Linux/2014-09/107005.htm
Spring 3整合Quartz 2實現定時任務 http://www.linuxidc.com/Linux/2014-09/107006.htm
Java項目中定時任務之Quartz的應用 http://www.linuxidc.com/Linux/2013-12/94443.htm
Spring 3 調度器示例 —— JDK 定時器和 Quartz 展示 http://www.linuxidc.com/Linux/2013-10/91946.htm