Quartz源碼分析（二）

原文位址：http://smurfs.iteye.com/blog/1157692

Quartz架構執行的任務需要寫在一個實作Job接口的類中，在實作類中的execute(JobExecutionContext context)中執行相關的操作，通過實作Job接口來使你的Java 元件可以很簡單的被scheduler執行，下面是job接口：

/**
     * <p>
     * Called by the <code>{@link Scheduler}</code> when a <code>{@link Trigger}</code>
     * fires that is associated with the <code>Job</code>.
     * </p>
     * 
     * <p>
     * The implementation may wish to set a 
     * {@link JobExecutionContext#setResult(Object) result} object on the 
     * {@link JobExecutionContext} before this method exits.  The result itself
     * is meaningless to Quartz, but may be informative to 
     * <code>{@link JobListener}s</code> or 
     * <code>{@link TriggerListener}s</code> that are watching the job's 
     * execution.
     * </p>
     * 
     * @throws JobExecutionException
     *           if there is an exception while executing the job.
     */
    void execute(JobExecutionContext context)
        throws JobExecutionException;
           

如上，你會看到job觸發器出發時，job的execute方法會被執行。那麼，scheduler的job是通過何種方式建立和執行的呢。先來看看job的部署，job是通過jobdetail scheduler到架構中去的，然後通過getJobClass()方法擷取到job實作類的class位元組碼的，通過jobFactory的newJob()方法反射出Java 的具體執行個體，然後在JobRunShell線程對象的run方法中執行。

1、  先看看jobdetail的建立，在quartz2.2.1中，jobdetail是通過jobbuilder建立

/**
     * Produce the <code>JobDetail</code> instance defined by this 
     * <code>JobBuilder</code>.
     * 
     * @return the defined JobDetail.
     */
    public JobDetail build() {

        JobDetailImpl job = new JobDetailImpl();
        
        job.setJobClass(jobClass);
        job.setDescription(description);
        if(key == null)
            key = new JobKey(Key.createUniqueName(null), null);
        job.setKey(key); 
        job.setDurability(durability);
        job.setRequestsRecovery(shouldRecover);
        
        
        if(!jobDataMap.isEmpty())
            job.setJobDataMap(jobDataMap);
        
        return job;
    }
           

Jobbuilder 通過靜态方法 newjob() 不同重載來建立 Jobbuilder ，通過 withIdentity() 重載設定參數，如下：

/**
     * Create a JobBuilder with which to define a <code>JobDetail</code>,
     * and set the class name of the <code>Job</code> to be executed.
     * 
     * @return a new JobBuilder
     */
    public static JobBuilder newJob(Class <? extends Job> jobClass) {
        JobBuilder b = new JobBuilder();
        b.ofType(jobClass);
        return b;
    }
           

/**
     * Use a <code>JobKey</code> with the given name and default group to
     * identify the JobDetail.
     * 
     * <p>If none of the 'withIdentity' methods are set on the JobBuilder,
     * then a random, unique JobKey will be generated.</p>
     * 
     * @param name the name element for the Job's JobKey
     * @return the updated JobBuilder
     * @see JobKey
     * @see JobDetail#getKey()
     */
    public JobBuilder withIdentity(String name) {
        key = new JobKey(name, null);
        return this;
    }
           

2、  建立好jobdetail後，scheduler通過線程類JobRunShell來執行Job。

通過initialize方法中調用JobFactory的newJob()建立Job執行個體。

public void initialize(QuartzScheduler sched)
        throws SchedulerException {
        this.qs = sched;

        Job job = null;
        JobDetail jobDetail = firedTriggerBundle.getJobDetail();

        try {
            job = sched.getJobFactory().newJob(firedTriggerBundle, scheduler);
        } catch (SchedulerException se) {
            sched.notifySchedulerListenersError(
                    "An error occured instantiating job to be executed. job= '"
                            + jobDetail.getKey() + "'", se);
            throw se;
        } catch (Throwable ncdfe) { // such as NoClassDefFoundError
            SchedulerException se = new SchedulerException(
                    "Problem instantiating class '"
                            + jobDetail.getJobClass().getName() + "' - ", ncdfe);
            sched.notifySchedulerListenersError(
                    "An error occured instantiating job to be executed. job= '"
                            + jobDetail.getKey() + "'", se);
            throw se;
        }

        this.jec = new JobExecutionContextImpl(scheduler, firedTriggerBundle, job);
    }
           

JobFactory 的 newJob() 方法通過反射使用預設無參數的構造方法實作 job 執行個體建立，如下：

public Job newJob(TriggerFiredBundle bundle, Scheduler Scheduler) throws SchedulerException {

        JobDetail jobDetail = bundle.getJobDetail();
        Class<? extends Job> jobClass = jobDetail.getJobClass();
        try {
            if(log.isDebugEnabled()) {
                log.debug(
                    "Producing instance of Job '" + jobDetail.getKey() + 
                    "', class=" + jobClass.getName());
            }
            
            return jobClass.newInstance();
        } catch (Exception e) {
            SchedulerException se = new SchedulerException(
                    "Problem instantiating class '"
                            + jobDetail.getJobClass().getName() + "'", e);
            throw se;
        }
    }
           

Job 的執行很簡單，直接調用 execute 方法即可：

public QuartzScheduler(QuartzSchedulerResources resources, long idleWaitTime, @Deprecated long dbRetryInterval)
        throws SchedulerException {
        this.resources = resources;
        if (resources.getJobStore() instanceof JobListener) {
            addInternalJobListener((JobListener)resources.getJobStore());
        }

        this.schedThread = new QuartzSchedulerThread(this, resources);
        ThreadExecutor schedThreadExecutor = resources.getThreadExecutor();
        schedThreadExecutor.execute(this.schedThread);
        if (idleWaitTime > 0) {
            this.schedThread.setIdleWaitTime(idleWaitTime);
        }

        jobMgr = new ExecutingJobsManager();
        addInternalJobListener(jobMgr);
        errLogger = new ErrorLogger();
        addInternalSchedulerListener(errLogger);

        signaler = new SchedulerSignalerImpl(this, this.schedThread);
        
        if(shouldRunUpdateCheck()) 
            updateTimer = scheduleUpdateCheck();
        else
            updateTimer = null;
        
        getLog().info("Quartz Scheduler v." + getVersion() + " created.");
    }
           

Job 的實作和執行很簡單，   主要是業務邏輯，以下簡單的把類之間的關系整理下：