Retry Logic
Spring Batch includes retry logic which lets configure and manage the number of attempts the process will attempt when encountering a non-fatal error. Non-fatal errors usually pass with a retry and tend to be temporary problems. Using retry logic in your batch processing tasks makes the jobs more robust, in that before labeling a job as a failure, an unsuccessful one is tried again. Below are steps that can be followed to implement retry logic in Spring Batch:
1. Identify the Batch Step:
The first step is to identify the specific batch step where you want to implement retry logic. You typically apply retry logic to a chunk-based step, where data is read, processed, and written in chunks.
2. Configure the Step:
Use StepBuilderFactory to create and configure the batch step in your Spring Batch configuration. Below is an example
Java
@Beanpublic Step myStep() { return stepBuilderFactory.get("myStep") .<Input, Output>chunk(10) // Chunk size .reader(reader()) .processor(processor()) .writer(writer()) .faultTolerant() // Enable fault tolerance .retryLimit(3) // Number of retry attempts .retry(Exception.class) // Retry on specific exception(s) .backOffPolicy(new ExponentialBackOffPolicy()) // Optional backoff policy .listener(new MyRetryListener()) // Custom retry listener (optional) .build(); } |
Where,
- chunk(10): This defines the chunk size. It specifies how many items should be read, processed, and written in each transaction. You can adjust this value based on your requirements.
- faultTolerant(): This method enables fault tolerance for the step, allowing you to configure retry and skip logic.
- retryLimit(3): This sets the maximum number of retry attempts for each item in the chunk. In this example, it’s set to 3, meaning each item will be retried up to 3 times if an exception occurs.
- retry(Exception.class): This specifies the type of exception(s) that should trigger a retry. In this case, it’s set to retry on any exception of type Exception. You can customize this to retry on specific exceptions relevant to your use case.
- backOffPolicy(): Optionally, you can configure a backoff policy to introduce delays between retry attempts. The ExponentialBackOffPolicy is one of the available policies.
- listener(): You can attach a custom retry listener to the step if you want to perform actions or logging during retries. This is optional but can be useful for monitoring and custom handling.
3. Implement Custom Retry Listeners (Optional)
If you attached a custom retry listener using listener(), you need to implement the listener as a Spring bean. A custom retry listener can be used to perform actions before and after each retry attempt. For example, you can log retry attempts or customize the behaviour:
Java
public class MyRetryListener implements RetryListener { @Override public <T, S> boolean open(RetryContext context, RetryCallback<T, S> callback) { // Code to run before a retry attempt return true; } @Override public <T, S> void close(RetryContext context, RetryCallback<T, S> callback, Throwable throwable) { // Code to run after a retry attempt, regardless of success or failure } @Override public <T, S> void onError(RetryContext context, RetryCallback<T, S> callback, Throwable throwable) { // Code to run when a retryable exception occurs } } |
4. Handle Exceptions in ItemProcessor (Optional)
If you want to apply retry logic specifically to exceptions thrown by your ItemProcessor, make sure your ItemProcessor is designed to throw these exceptions when necessary. Spring Batch will then catch these exceptions and apply the retry logic as configured.
5. Run Your Batch Job
With retry logic configured, you can now run your Spring Batch job. When exceptions occur during item processing, Spring Batch will automatically retry items based on your configuration. If the maximum number of retries is reached or if the retry logic determines that no more retries should be attempted, Spring Batch will proceed to the next item or take appropriate action based on your configuration.
Spring Batch – Configuring Retry and Skip Logic
Retry and skip logic are essential features in Spring Batch that help manage errors and exceptions during batch processing. They ensure that batch jobs can recover from failures and continue processing data without causing job failures. Here’s an explanation of retry and skip logic in Spring Batch: