[[howto.batch]]
= Batch Applications

A number of questions often arise when people use Spring Batch from within a Spring Boot application.
This section addresses those questions.



[[howto.batch.specifying-a-data-source]]
== Specifying a Batch Data Source

By default, batch applications require a javadoc:javax.sql.DataSource[] to store job details.
Spring Batch expects a single javadoc:javax.sql.DataSource[] by default.
To have it use a javadoc:javax.sql.DataSource[] other than the application’s main javadoc:javax.sql.DataSource[], declare a javadoc:javax.sql.DataSource[] bean, annotating its javadoc:org.springframework.context.annotation.Bean[format=annotation] method with javadoc:org.springframework.boot.autoconfigure.batch.BatchDataSource[format=annotation].
If you do so and want two data sources (for example by retaining the main auto-configured javadoc:javax.sql.DataSource[]), set the `defaultCandidate` attribute of the javadoc:org.springframework.context.annotation.Bean[format=annotation] annotation to `false`.
To take greater control, add javadoc:org.springframework.batch.core.configuration.annotation.EnableBatchProcessing[format=annotation] to one of your javadoc:org.springframework.context.annotation.Configuration[format=annotation] classes or extend javadoc:org.springframework.batch.core.configuration.support.DefaultBatchConfiguration[].
See the API documentation of javadoc:{url-spring-batch-javadoc}/org.springframework.batch.core.configuration.annotation.EnableBatchProcessing[format=annotation]
and javadoc:{url-spring-batch-javadoc}/org.springframework.batch.core.configuration.support.DefaultBatchConfiguration[] for more details.

For more info about Spring Batch, see the {url-spring-batch-site}[Spring Batch project page].



[[howto.batch.specifying-a-transaction-manager]]
== Specifying a Batch Transaction Manager

Similar to xref:batch.adoc#howto.batch.specifying-a-data-source[], you can define a javadoc:org.springframework.transaction.PlatformTransactionManager[] for use in batch processing by annotating its javadoc:org.springframework.context.annotation.Bean[format=annotation] method with javadoc:org.springframework.boot.autoconfigure.batch.BatchTransactionManager[format=annotation].
If you do so and want two transaction managers (for example by retaining the auto-configured javadoc:org.springframework.transaction.PlatformTransactionManager[]), set the `defaultCandidate` attribute of the javadoc:org.springframework.context.annotation.Bean[format=annotation] annotation to `false`.



[[howto.batch.specifying-a-task-executor]]
== Specifying a Batch Task Executor

Similar to xref:batch.adoc#howto.batch.specifying-a-data-source[], you can define a javadoc:org.springframework.core.task.TaskExecutor[] for use in batch processing by annotating its javadoc:org.springframework.context.annotation.Bean[format=annotation] method with javadoc:org.springframework.boot.autoconfigure.batch.BatchTaskExecutor[format=annotation].
If you do so and want two task executors (for example by retaining the auto-configured javadoc:org.springframework.core.task.TaskExecutor[]), set the `defaultCandidate` attribute of the javadoc:org.springframework.context.annotation.Bean[format=annotation] annotation to `false`.



[[howto.batch.running-jobs-on-startup]]
== Running Spring Batch Jobs on Startup

Spring Batch auto-configuration is enabled by adding `spring-boot-starter-batch` to your application's classpath.

If a single javadoc:org.springframework.batch.core.Job[] bean is found in the application context, it is executed on startup (see javadoc:org.springframework.boot.autoconfigure.batch.JobLauncherApplicationRunner[] for details).
If multiple javadoc:org.springframework.batch.core.Job[] beans are found, the job that should be executed must be specified using configprop:spring.batch.job.name[].

To disable running a javadoc:org.springframework.batch.core.Job[] found in the application context, set the configprop:spring.batch.job.enabled[] to `false`.

See {code-spring-boot-autoconfigure-src}/batch/BatchAutoConfiguration.java[`BatchAutoConfiguration`] for more details.



[[howto.batch.running-from-the-command-line]]
== Running From the Command Line

Spring Boot converts any command line argument starting with `--` to a property to add to the javadoc:org.springframework.core.env.Environment[], see xref:reference:features/external-config.adoc#features.external-config.command-line-args[accessing command line properties].
This should not be used to pass arguments to batch jobs.
To specify batch arguments on the command line, use the regular format (that is without `--`), as shown in the following example:

[source,shell]
----
$ java -jar myapp.jar someParameter=someValue anotherParameter=anotherValue
----

If you specify a property of the javadoc:org.springframework.core.env.Environment[] on the command line, it is ignored by the job.
Consider the following command:

[source,shell]
----
$ java -jar myapp.jar --server.port=7070 someParameter=someValue
----

This provides only one argument to the batch job: `someParameter=someValue`.



[[howto.batch.restarting-a-failed-job]]
== Restarting a Stopped or Failed Job

To restart a failed javadoc:org.springframework.batch.core.Job[], all parameters (identifying and non-identifying) must be re-specified on the command line.
Non-identifying parameters are *not* copied from the previous execution.
This allows them to be modified or removed.

NOTE: When you're using a custom javadoc:org.springframework.batch.core.JobParametersIncrementer[], you have to gather all parameters managed by the incrementer to restart a failed execution.



[[howto.batch.storing-job-repository]]
== Storing the Job Repository

Spring Batch requires a data store for the javadoc:org.springframework.batch.core.Job[] repository.
If you use Spring Boot, you must use an actual database.
Note that it can be an in-memory database, see {url-spring-batch-docs}/job.html#configuringJobRepository[Configuring a Job Repository].
