improve experience when configuring an alternative JobRepository

[joshlong]

improve experience when configuring an alternative JobRepository, as the DefaultBatchConfiguration, upon which Spring Boot in turn relies, assumes only JDBC-based infrastructure. This means that, when using Spring Boot, you can't simply replace one bean of type JobRepository and have things work. Everything must be redone from scratch, as we used to do before Spring Boot existed.

This will be a problem for users of Spring Batch who want to avail themselves of the new "resourceless" and MongoDB job repository alternatives.

[fmbenhassine]

@EnableBatchProcessing (and in turn DefaultBatchConfiguration) was designed as the Java counterpart of the XML element job-repository from the batch namespace where a datasource is required:

<batch:job-repository id="jobRepository" data-source="dataSource" transaction-manager="transactionManager"/>

So yes, @EnableBatchProcessing assumes a JDBC infrastructure, and this should change now that we introduced the mongo job repository and the resourceless job repository.

I have a couple ideas on how we can address this issue and of course I am open to any thoughts about this as well. I will share these ideas with the community when we start working on this design issue for the next major release. This comment is only to validate and acknowledge the issue. Thank you for reporting it, @joshlong !