Mastering the SkipPolicyFailedException in Spring Batch

Exploring and unlocking the potential of the powerful SkipPolicyFailedException in Spring Batch, through code examples and intricate details you must know!

In the ocean of batch processing, the Spring Batch framework is undoubtedly one of the most convenient, powerful, and versatile tools developers hold dear. Its carefully crafted programming model handy for large volume applications, cloud-based functionality, and extensive set of services and APIs are a testament to its prowess. However, to harness Spring Batch fully, it is crucial to understand various exceptions and how to handle them. This article aims to deep dive into the SkipPolicyFailedException.

What is the SkipPolicyFailedException?

In simple terms, SkipPolicyFailedException occurs when a developer-configured skip policy, in essence, a strategy to deal with record errors, is unable to determine whether to skip an item or not in a batch job. But before we get into the SkipPolicyFailedException in detail, let’s understand the context in which it operates.

Job job = jobBuilders.get("job").start(step).build();
Step step = stepBuilders.get("step")
    .<String, String> chunk(10)
      .reader(flatFileItemReader())
      .writer(itemWriter())
      .faultTolerant()
      .skipPolicy(jobSkipPolicy())
    .build();

Setting up a SkipPolicy

In Spring Batch, you can define a custom SkipPolicy by implementing the SkipPolicy interface. Here’s an example:

public class CustomSkipPolicy implements SkipPolicy {

    @Override
    public boolean shouldSkip(Throwable exception, int skipCount) throws SkipLimitExceededException {
        if(exception instanceof CustomException && skipCount < 5 ){
            return true;
        } else {
            return false;
        }
    }
}

In the above example, the CustomSkipPolicy will skip the record when it throws a CustomException and has not been skipped more than five times. Now, suppose you want to throw a SkipPolicyFailedException, that can be done by changing the shouldSkip method:

@Override
public boolean shouldSkip(Throwable exception, int skipCount) throws SkipLimitExceededException {
    if(exception instanceof CustomException && skipCount < 5 ){
        return true;
    } else {
        throw new SkipPolicyFailedException(exception);
    }
}

The SkipPolicyFailedException will wrap around the original exception, effectively relaying the root cause of the issue.

Handling the SkipPolicyFailedException

Now, once we know the skip policy can fail and cause an exception, it’s essential to know how to handle it effectively. To handle the exception, we can create an Exception Handler class.

public class CustomExceptionHandler implements ExceptionHandler {
 
    @Override
    public void handleException(RepeatContext context, Throwable throwable) throws Throwable {
        if(throwable.getCause() instanceof SkipPolicyFailedException) {
            System.out.println("Handling SkipPolicyFailedException: " + throwable.getMessage());
        } 
        throw throwable;
    }
}

In the above code snippet, the ExceptionHandler class catches the SkipPolicyFailedException, and handles it by displaying a custom message to the console.

Closing Thoughts

Understanding the nuts and bolts of Spring Batch exceptions like SkipPolicyFailedException helps write more robust solutions in batch processing. It equips you to manage batch situations that deviate from a happy path, and handle them with utmost effectiveness.

While Spring Batch can seem overwhelming given its expansive nature, focusing on one aspect at a time, like we did today with SkipPolicyFailedException, can simplify the learning curve and yield a much better grasp of this fantastic framework!

References

• Spring Batch Documentation
• Spring’s Exception Handling
• Spring Batch’s SkipPolicy Interface
• SkipPolicyFailedException

Stay tuned for more technical deep-dives into the alluring world of Spring Batch!