15. Spring Batch Events

15. Spring Batch Events
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When executing a Spring Batch job through a task, Spring Cloud Task can be configured to emit informational messages based on the Spring Batch listeners available in Spring Batch. Specifically, the following Spring Batch listeners are autoconfigured into each batch job and emit messages on the associated Spring Cloud Stream channels when run through Spring Cloud Task:

JobExecutionListener listens for job-execution-events
StepExecutionListener listens for step-execution-events
ChunkListener listens for chunk-events
ItemReadListener listens for item-read-events
ItemProcessListener listens for item-process-events
ItemWriteListener listens for item-write-events
SkipListener listens for skip-events

These listeners are autoconfigured into any AbstractJob when the appropriate beans (a Job and a TaskLifecycleListener) exist in the context. Configuration to listen to these events is handled the same way binding to any other Spring Cloud Stream channel is done. Our task (the one running the batch job) serves as a Source, with the listening applications serving as either a Processor or a Sink.

An example could be to have an application listening to the job-execution-events channel for the start and stop of a job. To configure the listening application, you would configure the input to be job-execution-events as follows:

spring.cloud.stream.bindings.input.destination=job-execution-events

	Note
	A binder implementation is also required to be on the classpath.

	Note
	A sample batch event application can be found in the samples module of the Spring Cloud Task Project, here.

15.1 Sending Batch Events to Different Channels

One of the options that Spring Cloud Task offers for batch events is the ability to alter the channel to which a specific listener can emit its messages. To do so, use the following configuration: spring.cloud.stream.bindings.<the channel>.destination=<new destination>. For example, if StepExecutionListener needs to emit its messages to another channel called my-step-execution-events instead of the default step-execution-events, you can add the following configuration:

spring.cloud.stream.bindings.step-execution-events.destination=my-step-execution-events

15.2 Disabling Batch Events

To disable the listener functionality for all batch events, use the following configuration:

spring.cloud.task.batch.events.enabled=false

To disable a specific batch event, use the following configuration:

spring.cloud.task.batch.events.<batch event listener>.enabled=false:

The following listing shows individual listeners that you can disable:

spring.cloud.task.batch.events.job-execution.enabled=false
spring.cloud.task.batch.events.step-execution.enabled=false
spring.cloud.task.batch.events.chunk.enabled=false
spring.cloud.task.batch.events.item-read.enabled=false
spring.cloud.task.batch.events.item-process.enabled=false
spring.cloud.task.batch.events.item-write.enabled=false
spring.cloud.task.batch.events.skip.enabled=false

15.3 Emit Order for Batch Events

By default, batch events have Ordered.LOWEST_PRECEDENCE. To change this value (for example, to 5 ), use the following configuration:

spring.cloud.task.batch.events.job-execution-order=5
spring.cloud.task.batch.events.step-execution-order=5
spring.cloud.task.batch.events.chunk-order=5
spring.cloud.task.batch.events.item-read-order=5
spring.cloud.task.batch.events.item-process-order=5
spring.cloud.task.batch.events.item-write-order=5
spring.cloud.task.batch.events.skip-order=5

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