Job storage in Quartz using Files, A FileJobStore Class

Quartz supports mainly two types of Job Storage for Scheduler information.
• Memory (non persistent) storage


The memory job storage facility for Quartz is provided by a class called org.quartz.simpl.RAMJobStore, The RAMJobStore is the default, i.e unless you change the configuration, and this is the JobStore that will be used for any Quartz application. Using this JobStore has some advantage
1. Easy to configure, because already configured by Scheduler as a default
2. It’s fast - a plain old simple memory access
But, as a computer memory is volatile, when your Quartz application is stopped, it releases the memory back to the operating system. Of course, along with everything else stored in that released memory is the scheduling information.


• Persistent storage


Second is using database for Job storage which implements JobStoreSupport abstract class
Quartz offers two different types of concrete persistent JobStores, each one designed for a specific database environment and configuration:
1. org.quartz.impl.jdbcjobstore.JobStoreTX - Persistent Storage in a Stand-Alone Environment
2. org.quartz.impl.jdbcjobstore.JobStoreCMT - Persistent Storage in an Application Container
(For more information on this two concrete classes see, Quartz Docs)


This storage classes implements the JobStore interface.

Now to implement the FileJobStore for which saves our jobs in file by using serialization, we need to implement the JobStore interface

Implementing the JobStore Interface


The JobStore interface has 40 methods that must be implemented by any JobStore implementation, including user defined methods. How you implement those methods depends entirely on the type of JobStore that you are building. That doesn't mean that your JobStore will have only 40 methods; this is just the minimum that the interface requires. These 40 methods represent the public contract between a JobStore and the Scheduler.
Let's consider a method,
public void schedulerStarted() throws SchedulerException ;
The Scheduler calls the JobStore's schedulerStarted() method to inform the JobStore that the Scheduler has been started. If you look at the implementation in RAMJobStore, you can see that nothing is done inside this method for this implementation:



public void schedulerStarted() throws SchedulerException {
// nothing to do
}

The org.quartz.spi.JobStore interface has too many methods to list here, but the API for the JobStore interface can be generalized into the following categories:


• Job-related API
• Trigger-related API
• Calendar-related API
• Scheduler-related API


Quartz users almost never access or see concrete classes that implement the JobStore interface; they are used internally by the Quartz Scheduler to retrieve job and trigger information during runtime.
Now to implement FileJobStore, there are some important to method to override, eg

Store job

/**
Store the Job
*/
public void storeJob(SchedulingContext ctxt, JobDetail newJob,
boolean replaceExisting) throws ObjectAlreadyExistsException
{
// Here comes some other logic to store various parameters of Job
jobDetailMap.put(newJob.getName(), newJob);

}


/**
Called by the QuartzScheduler to inform the JobStore that it should free up all of it's resources because the scheduler is shutting down.
*/
public void shutdown()
{

log.info("SYSTEM IS SHUTTING DOWN .. SERILAZING THE JOBS ..");
// A temporary JobDetail object,
JobDetail jobDetailTemp = null;
try
{
// create the job.txt file to searilaze Jobs
objOutStream = new ObjectOutputStream(new FileOutputStream("job.txt", false));

// fetch each Job from joDetailMap
Iterator<Map.Entry<String, JobDetail>> it = jobDetailMap.entrySet().iterator();
// this list is serilized
ArrayList<JobDetail> jobDetailList = new ArrayList<JobDetail>();
while(it.hasNext())
{
jobDetailTemp = it.next().getValue();
// add Jobs to list
jobDetailList.add(jobDetailTemp);
}

// write to file
objOutStream.writeObject(jobDetailList);
objOutStream.flush();
objOutStream.close();
} catch (FileNotFoundException fnfex)
{
log.error("Problem in reading job file, job.txt; Exception " + fnfex.getMessage());
} catch (IOException ioex)
{
log.error("Problem in output stream; Exception :" + ioex.getMessage());
}
}

You can implement your own method for Job storage or enhance this code; I’m giving the source file of my implementation.
Download: FileJobStore.java
I know this implementation need some enhancements, as I’m not Java Guru, your comments are welcomed.
Updates: Removed a bug, new revision 1.2 of FileJobStore.java uploaded !!

Comments

Anonymous said…
Can you paste a link that works to your source code please?
Sagar Rohankar said…
@Anonymous - Sorry buddy, I lost that file somewhere...
Anonymous said…
Hey mate,

Any chance you can find the source code? I'm doing something similar to what you describe- would love to compare. Thanks!
Sagar Rohankar said…
The file is lost, but the implementation shouldn't be difficult. If you read post, you will know which methods are need to implement.

Popular Posts