Quartz

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Configuring Quartz with JDBCJobStore in Spring

I am starting a little series about Quartz scheduler internals, tips and tricks, this is a chapter 0 - how to configure persistent job store. In Quartz you essentially have a choice between storing jobs and triggers in memory and in a relation database ( Terracotta is a recent addition to the mix). I would say in 90% of the cases when you use

RAMJobStore

with Quartz you don't really need Quartz at all. Obviously this storage backend is transient and all your pending jobs and triggers are lost between restarts. If you are fine with that, much simpler and more lightweight solutions are available, including

ScheduledExecutorService

built into JDK and

@Scheduled(cron="*/5 * * * * MON-FRI")

in Spring. Can you justify using extra 0,5MiB JAR in this scenario?

This changes dramatically when you need clustering, fail-over, load-balancing and few other buzz-words. There are several use-cases for that:

• single server cannot handle required number of concurrent, long running jobs and the executions need to be split into several machines - but each task must be executed exactly ones
• we cannot afford to run jobs too late - if one server is down, another should run the job on time
• ...or less strictly - the job needs to run eventually - even if the one and only server was down for maintenance, delayed jobs need to be run as soon as possible after restart

In all cases above we need some sort of non-transient global storage to keep track which jobs were executed, so that they are run exactly ones by one machine. Relational database as a shared memory works good in this scenario.

So if you think you need to schedule jobs and have some of the requirements above, keep reading. I will show you how to configure Quartz with Spring and fully integrate them. First of all we need a

DataSource

:
? As you might have guessed, Quartz needs some database tables to work with. It does not create them automatically, but SQL scripts for several databases are provided, including H2 which as you can see I am using. I think Flyway is the easiest way to run database scripts on startup:

? BTW in case you haven't noticed: no, there is no XML in our sample application and yes, we are using Spring.

Let's move on to Quartz:
? It is nice to know you can inject instance of

@Configuration

annotated classes into another such class for convenience. Except that - nothing fancy. Note that we need

@DependsOn(Array("flyway"))

on Quartz scheduler factory - otherwise the scheduler might start before Flyway fired the migration script with Quartz database tables causing unpleasant errors on startup. The essential bits are

SpringBeanJobFactory

and

schedulerContextAsMap

. The special factory makes Spring responsible for creating

Job

instances. Unfortunately this factory is quite limited which we will see shortly in the following example. First we need a Spring bean and a Quartz job:
? First unexpected input is

@BeanProperty

instead of

@Autowired

or

@Resource

. Turns out that

Job

is not really a Spring bean, even though Spring creates an instance of it. Instead Spring discovers required dependencies using available setters. So where does the

msg

string come from? Keep going:
? Quartz 2.0 ships with a nice internal DSL for creating jobs and triggers in a readable manner. As you can see I am passing an extra

"Hello, world!"

parameter to the job. This parameter is stored in so called

JobData

in the database per job or per trigger. It will be provided to the job when it is executed. This way you can parametrize your jobs. However when executed our job throws

NullPointerException

... Apparently

printer

reference was not set and silently ignored. Turns out Spring won't simply look through all the beans available in the

ApplicationContext

. The

SpringBeanJobFactory

only looks into

Jobs'

and

Triggers'

JobData

and into so called scheduler context (already mentioned). If you want to inject any Spring bean into

Job

you must explicitly place a reference to that bean in

schedulerContext

:
? Unfortunately each and every Spring bean you want to inject to job has to be explicitly referenced in

schedulerContextMap

. Even worse, if you forget about it, Quartz will silently log NPE at runtime. In the future we will write more robust job factory. But for starters we have a working Spring + Quartz application ready for further experiments, sources as always available under my GitHub account.

You might ask yourself way can't we simply use MethodInvokingJobDetailFactoryBean? Well, first of all because it does not work with persistent job stores. Secondly - because it is unable to pass

JobData

to

Job

- so we can no longer distinguish between different job runs. For instance our job printing message would have to always print the same message hard-coded in the class.

BTW if anyone asks you: How many classes does a Java enterprise developer need to print “Hello world!" you can proudly reply: 4 classes, 30 JARs taking 20 MiB of space and a relational database with 10+ tables. Seriously, this is an output of our article here...

 

 

Quartz scheduler plugins - hidden treasure

Although briefly described in the official documentation, I believe Quartz plugins aren't known enough, looking at how useful they are.

Essentially plugins in Quartz are convenient classes wrapping registration of underlying listeners. You are free to write your own plugins but we will focus on existing ones shipped with Quartz.

LoggingTriggerHistoryPlugin

First some background. Two main abstractions in Quartz are jobs and triggers. Job is a piece of code that we would like to schedule. Trigger instructs the scheduler when this code should run. CRON (e.g. run every Friday between 9 AM and 5 PM until November) and simple (run 100 times every 2 hours) triggers are most commonly used. You associate any number of triggers to a single job.

Believe it or not, Quartz by default provides no logging or monitoring whatsoever of executed jobs and triggers. There is an API, but no built-in logging is implemented. It won't show you that it now executes this particular job due to this trigger firing. So the first thing you should do is adding the following lines to your

quartz.properties

:

? The first line (and the only required) loads the plugin class

LoggingTriggerHistoryPlugin

. The remaining lines are configuring the plugin, customizing the logging messages. I found the built-in defaults not very well thought, e.g. they display current time which is already part of the logging framework message. You are free to construct any logging message, see the API for details. Adding these extra few lines makes debugging and monitoring much easier:
? You see now why naming your triggers (

Demo.Every-few-seconds

) and jobs (

Demo.Print-message

) is so important.

LoggingJobHistoryPlugin

There is another handy plugin related to logging:
? The rule is the same - plugin + extra configuration. See JavaDoc of

LoggingJobHistoryPlugin

for details and possible placeholders. Quick look at logs reveals very descriptive output:
? I have no idea why these plugins aren't enabled by default. After all, if you don't want such a verbose output, you can turn it off in your logging framework. Never mind, I think it is a good idea to have them in place when troubleshooting Quartz execution.

XMLSchedulingDataProcessorPlugin

This is a pretty comprehensive plugin. It reads XML file (by default named

quartz_data.xml

) containing jobs and triggers definitions and adds them to the scheduler. This is especially useful when you have a global job that you need to add once. Plugin can either update the existing jobs/triggers or ignore the XML file if they already exist - very useful when JDBCJobStore is used.
? In the aforementioned article we have been manually adding job to the scheduler:
? The same can be achieved with XML configuration, just place the following

quartz_data.xml

in your CLASSPATH:
? The file supports both simple and CRON triggers and is well described using XML Schema. It is even possible to point out to an XML files somewhere in the file system and periodically scan them for changes (!) (see:

XMLSchedulingDataProcessorPlugin.setScanInterval()

. Guess what is Quartz using to schedule periodic scanning?
?

ShutdownHookPlugin

Last but not least,

ShutdownHookPlugin

. Small but probably useful plugin that register shutdown hook in the JVM in order to gently stop the scheduler. However I recommend turning

cleanShutdown

off - if the system already tries to abruptly stop the application (typically scheduler shutdown is called by Spring via

SchedulerFactoryBean

) or the user hit Ctrl+C - waiting for currently running jobs seems like a bad idea. After all, maybe we are killing the application because some jobs are running for too long/hunging?
? As you can see Qurtz ships with few quite interesting plugins. For some reason they aren't described in detail in the official documentation, but they work pretty well and are a valuable addition to scheduler.

The source code with applied plugins is available on GitHub.