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Improve Spring Batch coverage in reference documentation 

See gh-19211
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Jay Bryant 2019-12-02 12:59:42 -06:00 committed by Stephane Nicoll
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commit 6bd9b2ebc6
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spring-boot-project/spring-boot-docs/src/main/asciidoc/howto.adoc
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@ -2104,9 +2104,13 @@ 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.
[[howto-spring-batch-specifying-a-data-source]]
=== Specifying a Batch Data Source
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`.
@ -2115,26 +2119,54 @@ See {spring-batch-api}/core/configuration/annotation/EnableBatchProcessing.html[
For more about Spring Batch, see the {spring-batch}[Spring Batch project page].
[[howto-execute-spring-batch-jobs-on-startup]]
=== Execute Spring Batch Jobs on Startup
[[howto-running-spring-batch-jobs-on-startup]]
=== Running Spring Batch Jobs on Startup
Spring Batch auto-configuration is enabled by adding `@EnableBatchProcessing` (from Spring Batch) somewhere in your context.
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`).
====
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-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.
Spring Boot uses a class called `JobLaunchingCommandLineRunner`.
Spring Batch uses a class called `CommandLineJobRunner`.
They work a bit differently. However, for the most part, the differences do not cause trouble.
However, 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]
someParameter="someValue"
However, if you mean to not use the `someValue` value as the identifier for the `Job`, use two hyphens, as shown in the following example:
[source]
--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.
[[howto-spring-batch-storing-job-repository]]
=== Storing the Job Repository
Spring Batch requires a memory 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 https://docs.spring.io/spring-batch/trunk/reference/html/configureJob.html#configuringJobRepository[Configuring a Job Repository].
[[howto-actuator]]