@ -2104,36 +2104,75 @@ The preceding example overrides the default factory, and it should be applied to
[[howto-batch-applications]]
== Batch Applications
This section answers questions that arise from using Spring Batch with Spring Boot.
A number of questions often arise when people use Spring Batch from within a Spring Boot application.
This section addresses those questions.
NOTE: By default, batch applications require a `DataSource` to store job details.
Batch autowires a single `DataSource` in your context and uses that for processing.
To have Batch 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 create another one and mark it as `@Primary`.
[[howto-spring-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 about Spring Batch, see the {spring-batch}[Spring Batch project page].
For more info about Spring Batch, see the {spring-batch}[Spring Batch project page].
[[howto-execute-spring-batch-jobs-on-startup]]
=== Execute Spring Batch Jobs on Startup
Spring Batch auto-configuration is enabled by adding `@EnableBatchProcessing` (from Spring Batch) somewhere in your context.
[[howto-spring-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/JobLauncherCommandLineRunner.java[JobLauncherCommandLineRunner] for details).
By default, it executes *all* `Jobs` in the application context on startup (see {spring-boot-autoconfigure-module-code}/batch/JobLauncherCommandLineRunner.java[`JobLauncherCommandLineRunner`] 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).
[TIP]
.Specifying job parameters on the command line
====
Unlike command line option arguments that <<spring-boot-features.adoc#boot-features-external-config-command-line-args,set properties in the `Environment`>> (i.e. by starting with `--`, such as `--my-property=value`), job parameters have to be specified on the command line without dashes (e.g. `jobParam=value`).
====
See {spring-boot-autoconfigure-module-code}/batch/BatchAutoConfiguration.java[BatchAutoConfiguration] and {spring-batch-api}/core/configuration/annotation/EnableBatchProcessing.html[@EnableBatchProcessing] for more details.
[[howto-spring-batch-running-command-line]]
=== Running from the Command Line
Running Spring Batch with Spring Boot from the command line differs from running Spring Batch by itself from the command line.
The most important difference is that they parse command line arguments differently, which can cause trouble, as described in the next section.
==== Passing Command-line Arguments
Spring Boot uses `--` (two hyphens) to signal application arguments.
Spring Batch uses a single hyphen as a special marker on the `jobParameters` argument.
This section explains how to reconcile that difference when you use the `jobParameters` argument for Spring Batch within a Spring Boot application.
If you run Spring Batch with Spring Boot, Spring Boot strips the first `-` character from each command line argument.
For example, `--exampleArgument` becomes `-exampleArgument`.
Whether a command-line option has one hyphen or two often makes no difference in Spring Boot.
However, in Spring Batch, putting a single `-` character before the `jobParameters` parameter indicates that Spring Batch should not use the `jobParameters` value as the identifier for the `Job`.
Best practice is to use the `jobParameters` value as the identifier for the `Job`, so this issue may cause problems.
To avoid the issue, you should generally use no `-` characters for the command-line options that you pass to Spring Boot on behalf of Spring Batch, as shown in the following example:
[source,properties,indent=0]
----
someParameter=someValue
----
However, if you mean to not use `someValue` value as the identifier for the `Job`, use two hyphens, as shown in the following example:
[source,properties,indent=0]
----
--jobParameters=someValue
----
In the second example, Spring Boot passes the parameter to Spring Batch as `-jobParameters="someValue"`, and `someValue` is used as a non-identifying job parameter.
If the application context includes a `JobRegistry`, the jobs in `spring.batch.job.names` are looked up in the registry instead of being autowired from the context.
This is a common pattern with more complex systems, where multiple jobs are defined in child contexts and registered centrally.
See {spring-boot-autoconfigure-module-code}/batch/BatchAutoConfiguration.java[BatchAutoConfiguration] and https://github.com/spring-projects/spring-batch/blob/master/spring-batch-core/src/main/java/org/springframework/batch/core/configuration/annotation/EnableBatchProcessing.java[@EnableBatchProcessing] for more details.
[[howto-spring-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].
Stephane Nicoll
5 years ago