Spring Batch to process multiple Items at once

Question

We are using Spring Batch to do some processing, reading some ids via Reader and we want to process them as 'chunks' via a processor then write to multiple files. But the processor interface allows only one item to processed at a time, we need to do bulk processing because the processor depends on a third party and calling the service for each item is not an option.

I saw that we can create Wrappers for all Reader-Processor-Writers involved in the 'chunk' to handle List<> and delegate to some concrete reader/processor/writer. but that doesn't seem all nice to me. Like this:

   <batch:chunk reader="wrappedReader" processor="wrappedProcessor" writer="wrappedWriter" 
commit-interval="2"/>

Is there a 'chunking' option that lets chunking before the processor? rather than before Writer.

Cheers,

Answer 1

I'd recommend reconfiguring your ItemReader to return the "chunk" that needs to be processed since that's really the "item" you're processing is.

Answer 2

Since modifying the whole Spring Batch mechanic to process multiple items at once seems really complicated, I suggest you move your third party processing to a writer which actually can process a chunk of item at once.

Since you'll obviously need to maintain your current writer, you could simply use a CompositeItemWriter with 2 (or more) delegates : your new custom ItemWriter and your current one. The order of definition matters, since it will be the order in which they'll be called.

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UPDATE

Since using 2 distinct ItemWriter inside a CompositeItemWriter doesn't let you keep the modifications of the first one in the second one, you could also use an ItemWriteListener.

By implementing the method beforeWrite, you can call your third party with the actual chunk right before it's written :

@Override
public void beforeWrite(List<? extends T> items) {
    //Third party call on item chunk
}