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Question

I have a problem where in I need to receive a series of messages from an MQ queue and write this to a file and initiate a spring batch job with the file as input. Right now I'm thinking of launching the job with wired @Autowired JobLauncher jobLauncher and @Autowired Job job; from the MDB itself.But I feel this is not a good approach as spring batch may create a series of threads and EJB as such doesnt support multi threading.

Is there any other effective way to do this? I dont want to use quartz scheduler or anything else since it adds complexity. Is there any interface in spring batch itself which launches a job soon after a file comes in a directory? Any leads in doing this better would be appreciated.

Thanks.

Answer 1

• I have a problem where in I need to receive a series of messages from an MQ queue and write this to a file and initiate a spring batch job with the file as input

One way to do that would be engage a bit of Spring Integration, where you would have a file poller, that would poll for a new file:

<file:inbound-channel-adapter id="filePoller"
                              channel="filesAreComing" 
                              directory="file:${input.directory}"
                              filename-pattern="test*" />

Adapt a file message ( java.io.File ) to a file name ( String ), since that is what Spring Batch needs. This can be done with a JobLauncher adapter, that is already available from Spring Batch Admin here :

@ServiceActivator
public JobLaunchRequest adapt(File file) throws NoSuchJobException {

    JobParameters jobParameters = new JobParametersBuilder().addString(
            "input.file", file.getAbsolutePath()).toJobParameters();

    return new JobLaunchRequest(job, jobParameters);
}

wrap it to a JobLaunchRequest ( which is just a holder for a Job and JobParameters ) and send this request [as a message] to JobLaunchingMessageHandler :

<service-activator input-channel="jobLauncher">
    <beans:bean class="org.springframework.batch.integration.launch.JobLaunchingMessageHandler">
        <beans:constructor-arg ref="jobLauncher" />
    </beans:bean>
</service-activator>

that would launch the job.

"input.file" is a parameter that is bound at runtime ( hence #{...} ):

<bean id="reader" class="org.springframework.batch.item.file.FlatFileItemReader" scope="step">
    <property name="resource" value="#{jobParameters[input.file]}" />
    ... line mapper and other props
</bean>

Answer 2

I'm not sure I understand why you have a message queue, a message-driven POJO/EJB, AND a batch job.

One way to do it is to have the message driven POJO/EJB do the work. It's already an asynch process. You can pool the message driven beans so there are sufficient workers to handle the load. Why add complexity?

If you'd rather not do that, forget the queue and use Spring Batch on its own. I wouldn't do both.