This version is still in development and is not considered stable yet. For the latest stable version, please use Spring Batch Documentation 5.2.0!

Intercepting Step Execution

Just as with the Job, there are many events during the execution of a Step where a user may need to perform some functionality. For example, to write out to a flat file that requires a footer, the ItemWriter needs to be notified when the Step has been completed so that the footer can be written. This can be accomplished with one of many Step scoped listeners.

You can apply any class that implements one of the extensions of StepListener (but not that interface itself, since it is empty) to a step through the listeners element. The listeners element is valid inside a step, tasklet, or chunk declaration. We recommend that you declare the listeners at the level at which its function applies or, if it is multi-featured (such as StepExecutionListener and ItemReadListener), declare it at the most granular level where it applies.

  • Java

  • XML

The following example shows a listener applied at the chunk level in Java:

Java Configuration
@Bean
public Step step1(JobRepository jobRepository, PlatformTransactionManager transactionManager) {
	return new StepBuilder("step1", jobRepository)
				.<String, String>chunk(10, transactionManager)
				.reader(reader())
				.writer(writer())
				.listener(chunkListener())
				.build();
}

The following example shows a listener applied at the chunk level in XML:

XML Configuration
<step id="step1">
    <tasklet>
        <chunk reader="reader" writer="writer" commit-interval="10"/>
        <listeners>
            <listener ref="chunkListener"/>
        </listeners>
    </tasklet>
</step>

An ItemReader, ItemWriter, or ItemProcessor that itself implements one of the StepListener interfaces is registered automatically with the Step if using the namespace <step> element or one of the *StepFactoryBean factories. This only applies to components directly injected into the Step. If the listener is nested inside another component, you need to explicitly register it (as described previously under Registering ItemStream with a Step).

In addition to the StepListener interfaces, annotations are provided to address the same concerns. Plain old Java objects can have methods with these annotations that are then converted into the corresponding StepListener type. It is also common to annotate custom implementations of chunk components, such as ItemReader or ItemWriter or Tasklet. The annotations are analyzed by the XML parser for the <listener/> elements as well as registered with the listener methods in the builders, so all you need to do is use the XML namespace or builders to register the listeners with a step.

StepExecutionListener

StepExecutionListener represents the most generic listener for Step execution. It allows for notification before a Step is started and after it ends, whether it ended normally or failed, as the following example shows:

public interface StepExecutionListener extends StepListener {

    void beforeStep(StepExecution stepExecution);

    ExitStatus afterStep(StepExecution stepExecution);

}

ExitStatus has a return type of afterStep, to give listeners the chance to modify the exit code that is returned upon completion of a Step.

The annotations corresponding to this interface are:

  • @BeforeStep

  • @AfterStep

ChunkListener

A “chunk” is defined as the items processed within the scope of a transaction. Committing a transaction, at each commit interval, commits a chunk. You can use a ChunkListener to perform logic before a chunk begins processing or after a chunk has completed successfully, as the following interface definition shows:

public interface ChunkListener extends StepListener {

    void beforeChunk(ChunkContext context);
    void afterChunk(ChunkContext context);
    void afterChunkError(ChunkContext context);

}

The beforeChunk method is called after the transaction is started but before reading begins on the ItemReader. Conversely, afterChunk is called after the chunk has been committed (or not at all if there is a rollback).

The annotations corresponding to this interface are:

  • @BeforeChunk

  • @AfterChunk

  • @AfterChunkError

You can apply a ChunkListener when there is no chunk declaration. The TaskletStep is responsible for calling the ChunkListener, so it applies to a non-item-oriented tasklet as well (it is called before and after the tasklet).

ItemReadListener

When discussing skip logic previously, it was mentioned that it may be beneficial to log the skipped records so that they can be dealt with later. In the case of read errors, this can be done with an ItemReaderListener, as the following interface definition shows:

public interface ItemReadListener<T> extends StepListener {

    void beforeRead();
    void afterRead(T item);
    void onReadError(Exception ex);

}

The beforeRead method is called before each call to read on the ItemReader. The afterRead method is called after each successful call to read and is passed the item that was read. If there was an error while reading, the onReadError method is called. The exception encountered is provided so that it can be logged.

The annotations corresponding to this interface are:

  • @BeforeRead

  • @AfterRead

  • @OnReadError

ItemProcessListener

As with the ItemReadListener, the processing of an item can be “listened” to, as the following interface definition shows:

public interface ItemProcessListener<T, S> extends StepListener {

    void beforeProcess(T item);
    void afterProcess(T item, S result);
    void onProcessError(T item, Exception e);

}

The beforeProcess method is called before process on the ItemProcessor and is handed the item that is to be processed. The afterProcess method is called after the item has been successfully processed. If there was an error while processing, the onProcessError method is called. The exception encountered and the item that was attempted to be processed are provided, so that they can be logged.

The annotations corresponding to this interface are:

  • @BeforeProcess

  • @AfterProcess

  • @OnProcessError

ItemWriteListener

You can “listen” to the writing of an item with the ItemWriteListener, as the following interface definition shows:

public interface ItemWriteListener<S> extends StepListener {

    void beforeWrite(List<? extends S> items);
    void afterWrite(List<? extends S> items);
    void onWriteError(Exception exception, List<? extends S> items);

}

The beforeWrite method is called before write on the ItemWriter and is handed the list of items that is written. The afterWrite method is called after the items have been successfully written, but before committing the transaction associated with the chunk’s processing. If there was an error while writing, the onWriteError method is called. The exception encountered and the item that was attempted to be written are provided, so that they can be logged.

The annotations corresponding to this interface are:

  • @BeforeWrite

  • @AfterWrite

  • @OnWriteError

SkipListener

ItemReadListener, ItemProcessListener, and ItemWriteListener all provide mechanisms for being notified of errors, but none informs you that a record has actually been skipped. onWriteError, for example, is called even if an item is retried and successful. For this reason, there is a separate interface for tracking skipped items, as the following interface definition shows:

public interface SkipListener<T,S> extends StepListener {

    void onSkipInRead(Throwable t);
    void onSkipInProcess(T item, Throwable t);
    void onSkipInWrite(S item, Throwable t);

}

onSkipInRead is called whenever an item is skipped while reading. It should be noted that rollbacks may cause the same item to be registered as skipped more than once. onSkipInWrite is called when an item is skipped while writing. Because the item has been read successfully (and not skipped), it is also provided the item itself as an argument.

The annotations corresponding to this interface are:

  • @OnSkipInRead

  • @OnSkipInWrite

  • @OnSkipInProcess

SkipListeners and Transactions

One of the most common use cases for a SkipListener is to log out a skipped item, so that another batch process or even human process can be used to evaluate and fix the issue that leads to the skip. Because there are many cases in which the original transaction may be rolled back, Spring Batch makes two guarantees:

  • The appropriate skip method (depending on when the error happened) is called only once per item.

  • The SkipListener is always called just before the transaction is committed. This is to ensure that any transactional resources call by the listener are not rolled back by a failure within the ItemWriter.