Skip exceptions in spring-batch and commit error in database - spring-batch

Question

I'm using Spring batch to write a batch process and I'm having issues handling the exceptions.
I have a reader that fetches items from a database with an specific state. The reader passes the item to the processor step that can launch the exception MyException.class. When this exception is thrown I want to skip the item that caused that exception and continue reading the next one.
The issue here is that I need to change the state of that item in the database so it's not fetched again by the reader.
This is what I tried:
return this.stepBuilderFactory.get("name")
.<Input, Output>chunk(1)
.reader(reader())
.processor(processor())
.faultTolerant()
.skipPolicy(skipPolicy())
.writer(writer())
.build();
In my SkipPolicy class I have the next code:
public boolean shouldSkip(Throwable throwable, int skipCount) throws SkipLimitExceededException {
if (throwable instanceof MyException.class) {
// log the issue
// update the item that caused the exception in database so the reader doesn't return it again
return true;
}
return false;
}
With this code the exception is skipped and my reader is called again, however the SkipPolicy didn't commit the change or did a rollback, so the reader fetches the item and tries to process it again.
I also tried with an ExceptionHandler:
return this.stepBuilderFactory.get("name")
.<Input, Output>chunk(1)
.reader(reader())
.processor(processor())
.faultTolerant()
.skip(MyException.class)
.exceptionHandler(myExceptionHandler())
.writer(writer())
.build();
In my ExceptionHandler class I have the next code:
public void handleException(RepeatContext context, Throwable throwable) throws Throwable {
if (throwable.getCause() instanceof MyException.class) {
// log the issue
// update the item that caused the exception in database so the reader doesn't return it again
} else {
throw throwable;
}
}
With this solution the state is changed in the database, however it doesn't call the reader, instead it calls the method process of the processor() again, getting in an infinite loop.
I imagine I can use a listener in my step to handle the exceptions, but I don't like that solution because I will have to clone a lot of code asumming this exception could be launched in different steps/processors of my code.
What am I doing wrong?
EDIT: After a lot of tests and using different listeners like SkipListener, I couldn't achieve what I wanted, Spring Batch is always doing a rollback of my UPDATE.
Debugging this is what I found:
Once my listener is invoked and I update my item, the program enters the method write in the class FaultTolerantChunkProcessor (line #327).
This method will try the next code (copied from github):
try {
doWrite(outputs.getItems());
} catch (Exception e) {
status = BatchMetrics.STATUS_FAILURE;
if (rollbackClassifier.classify(e)) {
throw e;
}
/*
* If the exception is marked as no-rollback, we need to
* override that, otherwise there's no way to write the
* rest of the chunk or to honour the skip listener
* contract.
*/
throw new ForceRollbackForWriteSkipException(
"Force rollback on skippable exception so that skipped item can be located.", e);
}
The method doWrite (line #151) inside the class SimpleChunkProcessor will try to write the list of output items, however, in my case the list is empty, so in the line #159 (method writeItems) will launch an IndexOutOfBoundException, causing the ForceRollbackForWriteSkipException and doing the rollback I'm suffering.
If I override the class FaultTolerantChunkProcessor and I avoid writing the items if the list is empty, then everything works as intended, the update is commited and the program skips the error and calls the reader again.
I don't know if this is actually a bug or it's caused by something I'm doing wrong in my code.

Answer 1

A SkipListener is better suited to your use case than an ExceptionHandler in my opinion, as it gives you access to the item that caused the exception. With the exception handler, you need to carry the item in the exception or the repeat context.
Moreover, the skip listener allows you to know in which phase the exception happened (ie in read, process or write), while with the exception handler you need to find a way to detect that yourself. If the skipping code is the same for all phases, you can call the same method that updates the item's status in all the methods of the listener.