Quatz入门

Demo

SchedulerFactory schedFact = new org.quartz.impl.StdSchedulerFactory();

  Scheduler sched = schedFact.getScheduler();

  sched.start();

  // define the job and tie it to our HelloJob class
  JobDetail job = newJob(HelloJob.class)
      .withIdentity("myJob", "group1")// name, group
      .build();

  // Trigger the job to run now, and then every 40 seconds
  Trigger trigger = newTrigger()
      .withIdentity("myTrigger", "group1")
      .startNow()
      .withSchedule(simpleSchedule()
          .withIntervalInSeconds(40)
          .repeatForever())
      .build();

  // Tell quartz to schedule the job using our trigger
  sched.scheduleJob(job, trigger);

看以看到，一个Quatz分为三个部分，分别是Scheduler, Job, Trigger，后面会讲为什么trigger和job要分开。

Once a scheduler is instantiated, it can be started, placed in stand-by mode, and shutdown. Note that once a scheduler is shutdown, it cannot be restarted without being re-instaniated. Triggers do not fire(jobs do not execute) until the scheduler has been started, nor while it is in the paused state.

Jobs and Triggers

A Job is a class that implement the Job interface, which has only one simple method.

void execute(JobExecutionContext context)

When the Job’s trigger fires (more on that in a moment), the execute(..) method is invoked by one of the scheduler’s worker threads. The JobExecutionContext object that is passed to this method provides the job instance with information about its “run-time” environment - a handle to the Scheduler that executed it, a handle to the Trigger that triggered the execution, the job’s JobDetail object, and a few other items.

The JobDetail object is created by the Quartz client (your program) at the time the Job is added to the scheduler. It contains various property settings for the Job, as well as a JobDataMap, which can be used to store state information for a given instance of your job class. It is essentially the definition of the job instance, and is discussed in further detail in the next lesson.

Trigger objects are used to trigger the execution (or ‘firing’) of jobs. When you wish to schedule a job, you instantiate a trigger and ‘tune’ its properties to provide the scheduling you wish to have. Triggers may also have a JobDataMap associated with them - this is useful to passing parameters to a Job that are specific to the firings of the trigger. Quartz ships with a handful of different trigger types, but the most commonly used types are SimpleTrigger and CronTrigger.

SimpleTrigger is handy if you need ‘one-shot’ execution (just single execution of a job at a given moment in time), or if you need to fire a job at a given time, and have it repeat N times, with a delay of T between executions. CronTrigger is useful if you wish to have triggering based on calendar-like schedules - such as “every Friday, at noon” or “at 10:15 on the 10th day of every month.”

Why Jobs AND Triggers? Many job schedulers do not have separate notions of jobs and triggers. Some define a ‘job’ as simply an execution time (or schedule) along with some small job identifier. Others are much like the union of Quartz’s job and trigger objects. While developing Quartz, we decided that it made sense to create a separation between the schedule and the work to be performed on that schedule. This has (in our opinion) many benefits.

For example, Jobs can be created and stored in the job scheduler independent of a trigger, and many triggers can be associated with the same job. Another benefit of this loose-coupling is the ability to configure jobs that remain in the scheduler after their associated triggers have expired, so that that it can be rescheduled later, without having to re-define it. It also allows you to modify or replace a trigger without having to re-define its associated job.

More About Jobs and Job Details

Now consider the job class "HelloJob" defined as such:

public class HelloJob implements Job {

    public HelloJob() {
    }

    public void execute(JobExecutionContext context)
      throws JobExecutionException
    {
      System.err.println("Hello!  HelloJob is executing.");
    }
  }

Notice that we give the scheduler a JobDetail instance, and that it knows the type of job to be executed by simply providing the job's class as we build the JobDetail. 

Each (and every) time the scheduler executes the job, it creates a new instance of the class before calling its execute(..) method. When the execution is complete, references to the job class instance are dropped, and the instance is then garbage collected. One of the ramifications of this behavior is the fact that jobs must have a no-argument constructor (when using the default JobFactory implementation). Another ramification is that it does not make sense to have state data-fields defined on the job class - as their values would not be preserved between job executions.

You may now be wanting to ask "how can I provide properties/configuration for a Job instance?" and "how can I keep track of a job's state between executions?" The answer to these questions are the same: the key is the JobDataMap, which is part of the JobDetail object.

JobDataMap

The JobDataMap can be used to hold any amount of (serializable) data objects which you wish to have made available to the job instance when it executes. JobDataMap is an implementation of the Java Map interface, and has some added convenience methods for storing and retrieving data of primitive types.

 // define the job and tie it to our DumbJob class
  JobDetail job = newJob(DumbJob.class)
      .withIdentity("myJob", "group1") // name "myJob", group "group1"
      .usingJobData("jobSays", "Hello World!")
      .usingJobData("myFloatValue", 3.141f)
      .build();

Here's a quick example of getting data from the JobDataMap during the job's execution:

不太理解JobKey是干嘛用的

public class DumbJob implements Job {

    public DumbJob() {
    }

    public void execute(JobExecutionContext context)
      throws JobExecutionException
    {
      JobKey key = context.getJobDetail().getKey();

      JobDataMap dataMap = context.getJobDetail().getJobDataMap();

      String jobSays = dataMap.getString("jobSays");
      float myFloatValue = dataMap.getFloat("myFloatValue");

      System.err.println("Instance " + key + " of DumbJob says: " + jobSays + ", and val is: " + myFloatValue);
    }
  }

Be awared of the serialization problem when using self-defined type.

If you add setter methods to your job class that correspond to the names of keys in the JobDataMap (such as asetJobSays(String val) method for the data in the example above), then Quartz's default JobFactory implementation will automatically call those setters when the job is instantiated, thus preventing the need to explicitly get the values out of the map within your execute method.

Triggers can also have JobDataMaps associated with them. This can be useful in the case where you have a Job that is stored in the scheduler for regular/repeated use by multiple Triggers, yet with each independent triggering, you want to supply the Job with different data inputs.

每一个trigger还能携带数据信息，为自己的job instance提供数据。

The JobDataMap that is found on the JobExecutionContext during Job execution serves as a convenience. It is a merge of the JobDataMap found on the JobDetail and the one found on the Trigger, with the values in the latter overriding any same-named values in the former.

Here's a quick example of getting data from the JobExecutionContext's merged JobDataMap during the job's execution:

下面是提供set后的例子

public class DumbJob implements Job {


    String jobSays;
    float myFloatValue;
    ArrayList state;
      
    public DumbJob() {
    }

    public void execute(JobExecutionContext context)
      throws JobExecutionException
    {
      JobKey key = context.getJobDetail().getKey();

      JobDataMap dataMap = context.getMergedJobDataMap();  // Note the difference from the previous example

      state.add(new Date());

      System.err.println("Instance " + key + " of DumbJob says: " + jobSays + ", and val is: " + myFloatValue);
    }
    
    public void setJobSays(String jobSays) {
      this.jobSays = jobSays;
    }
    
    public void setMyFloatValue(float myFloatValue) {
      myFloatValue = myFloatValue;
    }
    
    public void setState(ArrayList state) {
      state = state;
    }
    
  }

是否需要加set函数取决于自己的喜好，它们本身也是各有利弊，没有哪个完全优越。

一个job可能取多个名字，取决于提供给他的参数，可能有个叫做“jobForA", "JobForB"

Lesson 4: More About Triggers

SimpleTrigger should meet your scheduling needs if you need to have a job execute exactly once at a specific moment in time, or at a specific moment in time followed by repeats at a specific interval. For example, if you want the trigger to fire at exactly 11:23:54 AM on January 13, 2015, or if you want it to fire at that time, and then fire five more times, every ten seconds.

Build a trigger for a specific moment in time, with no repeats:

SimpleTrigger trigger = (SimpleTrigger) newTrigger() 
    .withIdentity("trigger1", "group1")
    .startAt(myStartTime) // some Date 
    .forJob("job1", "group1") // identify job with name, group strings
    .build();

Build a trigger for a specific moment in time, then repeating every ten seconds ten times:

  trigger = newTrigger()
    .withIdentity("trigger3", "group1")
    .startAt(myTimeToStartFiring)  // if a start time is not given (if this line were omitted), "now" is implied
    .withSchedule(simpleSchedule()
        .withIntervalInSeconds(10)
        .withRepeatCount(10)) // note that 10 repeats will give a total of 11 firings
    .forJob(myJob) // identify job with handle to its JobDetail itself                   
    .build();

Build a trigger that will fire once, five minutes in the future:

 trigger = (SimpleTrigger) newTrigger() 
    .withIdentity("trigger5", "group1")
    .startAt(futureDate(5, IntervalUnit.MINUTE)) // use DateBuilder to create a date in the future
    .forJob(myJobKey) // identify job with its JobKey
    .build();

Build a trigger that will fire now, then repeat every five minutes, until the hour 22:00:

 trigger = newTrigger()
    .withIdentity("trigger7", "group1")
    .withSchedule(simpleSchedule()
        .withIntervalInMinutes(5)
        .repeatForever())
    .endAt(dateOf(22, 0, 0))
    .build();

Build a trigger that will fire at the top of the next hour, then repeat every 2 hours, forever:

trigger = newTrigger()
    .withIdentity("trigger8") // because group is not specified, "trigger8" will be in the default group
    .startAt(evenHourDate(null)) // get the next even-hour (minutes and seconds zero ("00:00"))
    .withSchedule(simpleSchedule()
        .withIntervalInHours(2)
        .repeatForever())
    // note that in this example, 'forJob(..)' is not called 
    //  - which is valid if the trigger is passed to the scheduler along with the job  
    .build();
            
    scheduler.scheduleJob(trigger, job);

最后，还有一些高级知识，比如listener, 序列化等等知识，用不到就暂时不看了。