[[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 `DataSource` to store job details.
Spring Batch expects a single `DataSource` by default.
To have it use a `DataSource` other than the application’s main `DataSource`, declare a `DataSource` bean, annotating its `@Bean` method with `@BatchDataSource`.
If you do so and want two data sources, remember to mark the other one `@Primary`.
To take greater control, implement `BatchConfigurer`.
See {spring-batch-api}/core/configuration/annotation/EnableBatchProcessing.html[The Javadoc of `@EnableBatchProcessing`] for more details.

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



[[howto.batch.running-jobs-on-startup]]
=== Running Spring Batch Jobs on Startup
Spring Batch auto-configuration is enabled by adding `@EnableBatchProcessing` to one of your `@Configuration` classes.

By default, it executes *all* `Jobs` in the application context on startup (see {spring-boot-autoconfigure-module-code}/batch/JobLauncherApplicationRunner.java[`JobLauncherApplicationRunner`] for details).
You can narrow down to a specific job or jobs by specifying `spring.batch.job.names` (which takes a comma-separated list of job name patterns).

See {spring-boot-autoconfigure-module-code}/batch/BatchAutoConfiguration.java[BatchAutoConfiguration] and {spring-batch-api}/core/configuration/annotation/EnableBatchProcessing.html[@EnableBatchProcessing] 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 `Environment`, see <<features#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 (i.e. without `--`), as shown in the following example:

[source,shell,indent=0,subs="verbatim"]
----
	$ java -jar myapp.jar someParameter=someValue anotherParameter=anotherValue
----

If you specify a property of the `Environment` on the command line, it is ignored by the job.
Consider the following command:

[source,shell,indent=0,subs="verbatim"]
----
	$ java -jar myapp.jar --server.port=7070 someParameter=someValue
----

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



[[howto.batch.storing-job-repository]]
=== Storing the Job Repository
Spring Batch requires a data store for the `Job` repository.
If you use Spring Boot, you must use an actual database.
Note that it can be an in-memory database, see {spring-batch-docs}job.html#configuringJobRepository[Configuring a Job Repository].