Quartz源碼節選（一）JobDetail與Trigger的創建

參考資料

• Quartz文檔譯文
• Quartz官方文檔
• Quartz源碼解析

第一篇配合第二篇閱讀，講解一些基本概念。若已瞭解可跳過。
推薦閱讀第三篇，因爲本文是基於第三篇的筆記。

DEMO

一個DEMO，每3秒輸出helloworld

public class MyJob implements Job {
    @Override
    public void execute(JobExecutionContext context) throws JobExecutionException {
        JobDataMap jobDataMap = context.getMergedJobDataMap();
        String say = jobDataMap.getString("say");
        System.out.println(say);
    }
}

public class Demo {
    public static void main(String[] args) {
        JobDetail jd = JobBuilder.newJob(MyJob.class)
                .withIdentity("myJob","jobGroup1")
                .withDescription("a demo jobDetail")
                .usingJobData("say","helloworld")
                .build(); //本文要講的部分

        CronTrigger cronTrigger = TriggerBuilder.newTrigger()
                .withIdentity("myCronTrigger","triggerGroup1")
                .withSchedule(CronScheduleBuilder.cronSchedule("0/3 * * * * ?"))
                .forJob(jd) //本文要講的部分
                .build(); //本文要講的部分
        
        try {
            Scheduler scheduler = new StdSchedulerFactory().getScheduler();
            scheduler.scheduleJob(jd,cronTrigger);
            scheduler.start();
        } catch (SchedulerException e) {
            e.printStackTrace();
        }
    }
}

JobDetail實例的創建

我們比較一下JobDetailImpl和JobBuilder的成員變量

public class JobDetailImpl implements Cloneable, java.io.Serializable, JobDetail {
    private static final long serialVersionUID = -6069784757781506897L;
    private String name;
    private String group = Scheduler.DEFAULT_GROUP;
    private String description;
    private Class<? extends Job> jobClass;
    private JobDataMap jobDataMap;
    private boolean durability = false;
    private boolean shouldRecover = false;
    private transient JobKey key = null;
}

public class JobBuilder {
    private JobKey key;
    private String description;
    private Class<? extends Job> jobClass;
    private boolean durability;
    private boolean shouldRecover;
    private JobDataMap jobDataMap = new JobDataMap();

JobDetail的創建是典型的builder模式。JobBuilder的成員變量和JobDetail相似。把想要的內容交給JobBuilder，JobBuilder在build()方法把對應成員賦給JobDetail。

• JobBuilder.buid()

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;
    }

Trigger實例的創建

和JobDetail類似，Trigger實例也是通過TriggerBuilder.build()獲得，但Trigger實例並不是由TriggerBuilder自己創建，而是委託給成員scheduleBuilder創建。

• TriggerBuilder.build()

public T build() {

        if(scheduleBuilder == null)
            scheduleBuilder = SimpleScheduleBuilder.simpleSchedule();
        MutableTrigger trig = scheduleBuilder.build(); //scheduleBuilder負責創建Trigger實例
        
        trig.setCalendarName(calendarName);
        trig.setDescription(description);
        trig.setStartTime(startTime);
        trig.setEndTime(endTime);
        if(key == null)
            key = new TriggerKey(Key.createUniqueName(null), null);
        trig.setKey(key); 
        if(jobKey != null)
            trig.setJobKey(jobKey);
        trig.setPriority(priority);
        
        if(!jobDataMap.isEmpty())
            trig.setJobDataMap(jobDataMap);
        
        return (T) trig;
    }

ScheduleBuilder有多種具體實現，這裏以CronScheduleBuilder爲例。

• CronScheduleBuilder.build()

public MutableTrigger build() {

        CronTriggerImpl ct = new CronTriggerImpl();

        ct.setCronExpression(cronExpression);
        ct.setTimeZone(cronExpression.getTimeZone());
        ct.setMisfireInstruction(misfireInstruction);

        return ct;
    }

scheduleBuilder成員是怎麼來的呢？是在TriggerBuilder設置觸發時間的時候

• TriggerBuilder.withSchedule(ScheduleBuilder schedBuilder)

public <SBT extends T> TriggerBuilder<SBT> withSchedule(ScheduleBuilder<SBT> schedBuilder) {
        this.scheduleBuilder = schedBuilder; //設置scheduleBuilder成員
        return (TriggerBuilder<SBT>) this;
    }

Trigger與JobDetail綁定

創建Trigger的時候可以指定對應的JobDetail

• TriggerBuilder.forJob(JobDetail jobDetail)

public TriggerBuilder<T> forJob(JobDetail jobDetail) {
        JobKey k = jobDetail.getKey();
        if(k.getName() == null)
            throw new IllegalArgumentException("The given job has not yet had a name assigned to it.");
        this.jobKey = k;
        return this;
    }

JobKey內容簡單，操作由Key來實現

public final class JobKey extends Key<JobKey> {

    private static final long serialVersionUID = -6073883950062574010L;
    
    public JobKey(String name) {
        super(name, null);
    }

    public JobKey(String name, String group) {
        super(name, group);
    }

    public static JobKey jobKey(String name) {
        return new JobKey(name, null);
    }
    
    public static JobKey jobKey(String name, String group) {
        return new JobKey(name, group);
    }

}