DDevelopment & Design

Chaining job execution in Quartz

  • byRafal P
  • February 2, 2011
  • 1 minute read

Quartz javaThere isn’t explicit way to chain jobs in Quartz. However this is still possible, by doing some tricks. Here is an explanation on how to do that (in very few words).

There are two ways to put job in chain:
– first one, by using Listeners( for example JobChainingJobListener),
– and the second one, by using JobDataMap which every job contains.
I prefer the second way with JobDataMaps. Why ? Because DataMaps are persistent so information about chained jobs survives restart of the server.

Chain is nothing more than normal queue of the jobs, so to put two jobs into chain we need to create queue from them. Queue should be bidirectional to allow easy manipulation. The idea is to put 4 properties into JobDataMaps:
– nextJobName, nextJobGroup – identify next job in chain
– previousJobName, previousJobGroup – identify previous job in chain

Those 4 variables are enough to implement standard bi-directional queue operations like: addJobToQueue(..), removeFromQueue(..), moveUp(..) and moveDown(..). One thing to remeber: adding job to chain should stop it, to avoid triggering jobs in unspecified order.

Last thing to do is to create own implementation of the Quartz Job interface which, in execute() method, will fire/trigger next job in chain, if there is any.

That’s all.

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DDevelopment & Design

Simple trick to DRY your Grails controller

Grails controllers are not very DRY. It's easy to find duplicated code fragments in default generated controller. Take a look at code sample below. It is duplicated four times in show, edit, update and delete actions:

class BookController {
def show() {
def bookInstance = Book.get(params.id)
if (!bookInstance) {
flash.message = message(code: 'default.not.found.message', args: [message(code: 'book.label', default: 'Book'), params.id])
redirect(action: "list")
return
        }
        [bookInstance: bookInstance]
    }
}

Why is it duplicated?

There is a reason for that duplication, though. If you move this snippet to a method, it can redirect to "list" action, but it can't prevent controller from further execution. After you call redirect, response status changes to 302, but after method exits, controller still runs subsequent code.

Solution

At TouK we've implemented a simple trick to resolve that situation:

  1. wrap everything with a simple withStoppingOnRender method,
  2. whenever you want to render or redirect AND stop controller execution - throw EndRenderingException.

We call it Big Return - return from a method and return from a controller at once. Here is how it works:

class BookController {
def show(Long id) {
withStoppingOnRender {
Book bookInstance = Book.get(id)
validateInstanceExists(bookInstance)
            [bookInstance: bookInstance]
        }
    }

protected Object withStoppingOnRender(Closure closure) {
try {
return closure.call()
        } catch (EndRenderingException e) {}
    }

private void validateInstanceExists(Book instance) {
if (!instance) {
flash.message = message(code: 'default.not.found.message', args: [message(code: 'book.label', default: 'Book'), params.id])
redirect(action: "list")
throw new EndRenderingException()
        }
    }
}

class EndRenderingException extends RuntimeException {}

Example usage

For simple CRUD controllers, you can use this solution and create some BaseController class for your controllers. We use withStoppingOnRender in every controller so code doesn't look like a spaghetti, we follow DRY principle and code is self-documented. Win-win-win! Here is a more complex example:

class DealerController {
@Transactional
def update() {
withStoppingOnRender {
Dealer dealerInstance = Dealer.get(params.id)
validateInstanceExists(dealerInstance)
validateAccountInExternalService(dealerInstance)
checkIfInstanceWasConcurrentlyModified(dealerInstance, params.version)
            dealerInstance.properties = params
saveUpdatedInstance(dealerInstance)
redirectToAfterUpdate(dealerInstance)
        }
    }
}