:spring_boot_version: 0.5.0.M6
:Component: http://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/stereotype/Component.html
:EnableAutoConfiguration: http://docs.spring.io/spring-boot/docs/{spring_boot_version}/api/org/springframework/boot/autoconfigure/EnableAutoConfiguration.html
:SpringApplication: http://docs.spring.io/spring-boot/docs/{spring_boot_version}/api/org/springframework/boot/SpringApplication.html
:toc:
:icons: font
:source-highlighter: prettify
:project_id: gs-batch-processing
This guide walks you through the process of creating a basic batch-driven solution.

== What you'll build

You'll build a service that imports data from a CSV spreadsheet, transforms it with custom code, and stores the final results in a database.


== What you'll need

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[[scratch]]
== Set up the project
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`build.gradle`
// AsciiDoc source formatting doesn't support groovy, so using java instead
[source,java]
----
include::initial/build.gradle[]
----

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Typically your customer or a business analyst supplies a spreadsheet. In this case, you make it up.

`src/main/resources/sample-data.csv`
[source,csv]
----
include::initial/src/main/resources/sample-data.csv[]
----

This spreadsheet contains a first name and a last name on each row, separated by a comma. This is a fairly common pattern that Spring handles out-of-the-box, as you will see.


Next, you write a SQL script to create a table to store the data.

`src/main/resources/schema-all.sql`
[source,sql]
----
include::initial/src/main/resources/schema-all.sql[]
----

NOTE: Spring Boot runs `schema-@@platform@@.sql` automatically during startup. `-all` is the default for all platforms.


[[initial]]
== Create a business class

Now that you see the format of data inputs and outputs, you write code to represent a row of data.

`src/main/java/hello/Person.java`
[source,java]
----
include::complete/src/main/java/hello/Person.java[]
----

You can instantiate the `Person` class either with first and last name through a constructor, or by setting the properties.


== Create an intermediate processor

A common paradigm in batch processing is to ingest data, transform it, and then pipe it out somewhere else. Here you write a simple transformer that converts the names to uppercase.

`src/main/java/hello/PersonItemProcessor.java`
[source,java]
----
include::complete/src/main/java/hello/PersonItemProcessor.java[]
----

`PersonItemProcessor` implements Spring Batch's `ItemProcessor` interface. This makes it easy to wire the code into a batch job that you define further down in this guide. According to the interface, you receive an incoming `Person` object, after which you transform it to an upper-cased `Person`.

NOTE: There is no requirement that the input and output types be the same. In fact, after one source of data is read, sometimes the application's data flow needs a different data type.


== Put together a batch job

Now you put together the actual batch job. Spring Batch provides many utility classes that reduce the need to write custom code. Instead, you can focus on the business logic.

`src/main/java/hello/BatchConfiguration.java`
[source,java]
----
include::complete/src/main/java/hello/BatchConfiguration.java[]
----

For starters, the `@EnableBatchProcessing` annotation adds many critical beans that support jobs and saves you a lot of leg work. This example uses a memory-based database (provided by `@EnableBatchProcessing`), meaning that when it's done, the data is gone.

Break it down:

`src/main/java/hello/BatchConfiguration.java`
[source,java]
----
include::/complete/src/main/java/hello/BatchConfiguration.java[tag=readerwriterprocessor]
----
.
The first chunk of code defines the input, processor, and output.
- `reader()` creates an `ItemReader`. It looks for a file called `sample-data.csv` and parses each line item with enough information to turn it into a `Person`.
- `processor()` creates an instance of our `PersonItemProcessor` you defined earlier, meant to uppercase the data.
- `write(DataSource)` creates an `ItemWriter`. This one is aimed at a JDBC destination and automatically gets a copy of the dataSource created by `@EnableBatchProcessing`. It includes the SQL statement needed to insert a single `Person` driven by Java bean properties.

The next chunk focuses on the actual job configuration.

`src/main/java/hello/BatchConfiguration.java`
[source,java]
----
include::/complete/src/main/java/hello/BatchConfiguration.java[tag=jobstep]
----
.
The first method defines the job and the second one defines a single step. Jobs are built from steps, where each step can involve a reader, a processor, and a writer. 

In this job definition, you need an incrementer because jobs use a database to maintain execution state. You then list each step, of which this job has only one step. The job ends, and the Java API produces a perfectly configured job.

In the step definition, you define how much data to write at a time. In this case, it writes up to ten records at a time. Next, you configure the reader, processor, and writer using the injected bits from earlier. 

NOTE: chunk() is prefixed `<Person,Person>` because it's a generic method. This represents the input and output types of each "chunk" of processing, and lines up with `ItemReader<Person>` and `ItemWriter<Person>`.


== Make the application executable

Although batch processing can be embedded in web apps and WAR files, the simpler approach demonstrated below creates a standalone application. You package everything in a single, executable JAR file, driven by a good old Java `main()` method.


`src/main/java/hello/Application.java`
[source,java]
----
include::complete/src/main/java/hello/Application.java[]
----

The `main()` method defers to the {SpringApplication}[`SpringApplication`] helper class, providing `Application.class` as an argument to its `run()` method. This tells Spring to read the annotation metadata from `Application` and to manage it as a component in the link:/understanding/application-context[Spring application context].

The `@ComponentScan` annotation tells Spring to search recursively through the `hello` package and its children for classes marked directly or indirectly with Spring's {Component}[`@Component`] annotation. This directive ensures that Spring finds and registers `BatchConfiguration`, because it is marked with `@Configuration`, which in turn is a kind of `@Component` annotation.

The {EnableAutoConfiguration}[`@EnableAutoConfiguration`] annotation switches on reasonable default behaviors based on the content of your classpath. For example, it looks for any class that implements the `CommandLineRunner` interface and invokes its `run()` method. In this case, it runs the demo code for this guide.

For demonstration purposes, there is code to create a `JdbcTemplate`, query the database, and print out the names of people the batch job inserts.

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:module: batch job
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The job prints out a line for each person that gets transformed. After the job runs, you can also see the output from querying the database.

....
Converting (firstName: Jill, lastName: Doe) into (firstName: JILL, lastName: DOE)
Converting (firstName: Joe, lastName: Doe) into (firstName: JOE, lastName: DOE)
Converting (firstName: Justin, lastName: Doe) into (firstName: JUSTIN, lastName: DOE)
Converting (firstName: Jane, lastName: Doe) into (firstName: JANE, lastName: DOE)
Converting (firstName: John, lastName: Doe) into (firstName: JOHN, lastName: DOE)
Found <firstName: JILL, lastName: DOE> in the database.
Found <firstName: JOE, lastName: DOE> in the database.
Found <firstName: JUSTIN, lastName: DOE> in the database.
Found <firstName: JANE, lastName: DOE> in the database.
Found <firstName: JOHN, lastName: DOE> in the database.
....


== Summary

Congratulations! You built a batch job that ingested data from a spreadsheet, processed it, and wrote it to a database.