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For a project I need to process items from one table and generate 3 different items for 3 different tables, all 3 in a second data source different from the one of the first item. The implementation is done with Spring Batch over Oracle DB. I think this question has something similar to what I need, but in there it is writing at the end only one different item.

To ilustrate the situation:

DataSource 1                               DataSource 2
------------                        ------------------------------

   Table A                          Table B     Table C    Table D

The reader should read one item from table A. In the processor, using the information from the item in A, 3 new items will be created of type B, C and D. In addition, the item from table A will be updated.

The writer should be able to write at the same time all 4 items. My first implementation is using a JpaItemWriter to update the item A, but I don't know how the processor could give the other 3 items to the writer in order to save all at the same time.

Can a processor return several items from different types? Would I need to create 4 steps, each one writing one of the items? And in this case, would that be error safe (If there is an error writing D, then A, B, and C would be rollback)?

Thanks in advance for your support!

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Daniel Rodríguez
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1 Answers1

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Your question is really two questions. Let's look at each individually:

Can an ItemProcessor return multiple items
An ItemProcessor can only return one item at a time for each item that is passed in. Because of this, in your specific scenario, you'll need your ItemProcessor to return a wrapper object that wraps items A, B, C, and D.

How can I write different types in the same step
Spring Batch relies heavily on composition in it's programming model. Since your ItemProcessor will be returning a wrapper object, you'll end up writing an ItemWriter that unwraps items A, B, C, and D and delegates the writing of each to the apropriate writer. So in the final solution, you'll end up with 5 ItemWriters: one for each item type and one that wraps all of those. Take a look at our CompositeItemWriter as an example here: https://github.com/spring-projects/spring-batch/blob/master/spring-batch-infrastructure/src/main/java/org/springframework/batch/item/support/CompositeItemWriter.java

Michael Minella
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