# Single Step Batch Job Starter

This section goes into how to develop a Spring Batch `Job` with a single `Step` by using the starter included in Spring Cloud Task. This starter lets you use configuration to define an `ItemReader`, an `ItemWriter`, or a full single-step Spring Batch `Job`. For more about Spring Batch and its capabilities, see the Spring Batch documentation.

To obtain the starter for Maven, add the following to your build:

    <dependency>
        <groupId>org.springframework.cloud</groupId>
        <artifactId>spring-cloud-starter-single-step-batch-job</artifactId>
        <version>2.3.0</version>
    </dependency>

To obtain the starter for Gradle, add the following to your build:

    compile "org.springframework.cloud:spring-cloud-starter-single-step-batch-job:2.3.0"

## Defining a Job

You can use the starter to define as little as an `ItemReader` or an `ItemWriter` or as much as a full `Job`. In this section, we define which properties are required to be defined to configure a `Job`.

### Properties

To begin, the starter provides a set of properties that let you configure the basics of a Job with one Step:

Table 1. Job Properties
Property | Type | Default Value | Description
--- | --- | --- | ---
`spring.batch.job.jobName` | `String` | `null` | The name of the job.
`spring.batch.job.stepName` | `String` | `null` | The name of the step.
`spring.batch.job.chunkSize` | `Integer` | `null` | The number of items to be processed per transaction.

With the above properties configured, you have a job with a single, chunk-based step. This chunk-based step reads, processes, and writes `Map<String, Object>` instances as the items. However, the step does not yet do anything. You need to configure an `ItemReader`, an optional `ItemProcessor`, and an `ItemWriter` to give it something to do. To configure one of these, you can either use properties and configure one of the options that has provided autoconfiguration or you can configure your own with the standard Spring configuration mechanisms.

| If you configure your own, the input and output types must match the others in the step. The `ItemReader` implementations and `ItemWriter` implementations in this starter all use a `Map<String, Object>` as the input and the output item.

## Autoconfiguration for ItemReader Implementations

This starter provides autoconfiguration for four different `ItemReader` implementations: `AmqpItemReader`, `FlatFileItemReader`, `JdbcCursorItemReader`, and `KafkaItemReader`. In this section, we outline how to configure each of these by using the provided autoconfiguration.

### AmqpItemReader

You can read from a queue or topic with AMQP by using the `AmqpItemReader`. The autoconfiguration for this `ItemReader` implementation is dependent upon two sets of configuration. The first is the configuration of an `AmqpTemplate`. You can either configure this yourself or use the autoconfiguration provided by Spring Boot. See the Spring Boot AMQP documentation. Once you have configured the `AmqpTemplate`, you can enable the batch capabilities to support it by setting the following properties:

Table 2. `AmqpItemReader` Properties
Property | Type | Default Value | Description
--- | --- | --- | ---
`spring.batch.job.amqpitemreader.enabled` | `boolean` | `false` | If `true`, the autoconfiguration will execute.
`spring.batch.job.amqpitemreader.jsonConverterEnabled` | `boolean` | `true` | Indicates if the `Jackson2JsonMessageConverter` should be registered to parse messages.

For more information, see the `AmqpItemReader` documentation.

### FlatFileItemReader

`FlatFileItemReader` lets you read from flat files (such as CSVs and other file formats). To read from a file, you can provide some components yourself through normal Spring configuration (`LineTokenizer`, `RecordSeparatorPolicy`, `FieldSetMapper`, `LineMapper`, or `SkippedLinesCallback`). You can also use the following properties to configure the reader:

Table 3. `FlatFileItemReader` Properties
Property | Type | Default Value | Description
--- | --- | --- | ---
`spring.batch.job.flatfileitemreader.saveState` | `boolean` | `true` | Determines if the state should be saved for restarts.
`spring.batch.job.flatfileitemreader.name` | `String` | `null` | Name used to provide unique keys in the `ExecutionContext`.
`spring.batch.job.flatfileitemreader.maxItemcount` | `int` | `Integer.MAX_VALUE` | Maximum number of items to be read from the file.
`spring.batch.job.flatfileitemreader.currentItemCount` | `int` | 0 | Number of items that have already been read. Used on restarts.
`spring.batch.job.flatfileitemreader.comments` | `List<String>` | empty List | A list of Strings that indicate commented lines (lines to be ignored) in the file.
`spring.batch.job.flatfileitemreader.resource` | `Resource` | `null` | The resource to be read.
`spring.batch.job.flatfileitemreader.strict` | `boolean` | `true` | If set to `true`, the reader throws an exception if the resource is not found.
`spring.batch.job.flatfileitemreader.encoding` | `String` | `FlatFileItemReader.DEFAULT_CHARSET` | Encoding to be used when reading the file.
`spring.batch.job.flatfileitemreader.linesToSkip` | `int` | 0 | Indicates the number of lines to skip at the start of a file.
`spring.batch.job.flatfileitemreader.delimited` | `boolean` | `false` | Indicates whether the file is a delimited file (CSV and other formats). Only one of this property or `spring.batch.job.flatfileitemreader.fixedLength` can be `true` at the same time.
`spring.batch.job.flatfileitemreader.delimiter` | `String` | `DelimitedLineTokenizer.DELIMITER_COMMA` | If reading a delimited file, indicates the delimiter to parse on.
`spring.batch.job.flatfileitemreader.quoteCharacter` | `char` | `DelimitedLineTokenizer.DEFAULT_QUOTE_CHARACTER` | Used to determine the character used to quote values.
`spring.batch.job.flatfileitemreader.includedFields` | `List<Integer>` | empty list | A list of indices to determine which fields in a record to include in the item.
`spring.batch.job.flatfileitemreader.fixedLength` | `boolean` | `false` | Indicates if a file’s records are parsed by column numbers. Only one of this property or `spring.batch.job.flatfileitemreader.delimited` can be `true` at the same time.
`spring.batch.job.flatfileitemreader.ranges` | `List<Range>` | empty list | List of column ranges by which to parse a fixed width record. See the Range documentation.
`spring.batch.job.flatfileitemreader.names` | `String []` | `null` | List of names for each field parsed from a record. These names are the keys in the `Map<String, Object>` in the items returned from this `ItemReader`.
`spring.batch.job.flatfileitemreader.parsingStrict` | `boolean` | `true` | If set to `true`, the mapping fails if the fields cannot be mapped.

See the `FlatFileItemReader` documentation.

### JdbcCursorItemReader

The `JdbcCursorItemReader` runs a query against a relational database and iterates over the resulting cursor (`ResultSet`) to provide the resulting items. This autoconfiguration lets you provide a `PreparedStatementSetter`, a `RowMapper`, or both. You can also use the following properties to configure a `JdbcCursorItemReader`:

Table 4. `JdbcCursorItemReader` Properties
Property | Type | Default Value | Description
--- | --- | --- | ---
`spring.batch.job.jdbccursoritemreader.saveState` | `boolean` | `true` | Determines whether the state should be saved for restarts.
`spring.batch.job.jdbccursoritemreader.name` | `String` | `null` | Name used to provide unique keys in the `ExecutionContext`.
`spring.batch.job.jdbccursoritemreader.maxItemcount` | `int` | `Integer.MAX_VALUE` | Maximum number of items to be read from the file.
`spring.batch.job.jdbccursoritemreader.currentItemCount` | `int` | 0 | Number of items that have already been read. Used on restarts.
`spring.batch.job.jdbccursoritemreader.fetchSize` | `int` |  | A hint to the driver to indicate how many records to retrieve per call to the database system. For best performance, you usually want to set it to match the chunk size.
`spring.batch.job.jdbccursoritemreader.maxRows` | `int` |  | Maximum number of items to read from the database.
`spring.batch.job.jdbccursoritemreader.queryTimeout` | `int` |  | Number of milliseconds for the query to timeout.
`spring.batch.job.jdbccursoritemreader.ignoreWarnings` | `boolean` | `true` | Determines whether the reader should ignore SQL warnings when processing.
`spring.batch.job.jdbccursoritemreader.verifyCursorPosition` | `boolean` | `true` | Indicates whether the cursor’s position should be verified after each read to verify that the `RowMapper` did not advance the cursor.
`spring.batch.job.jdbccursoritemreader.driverSupportsAbsolute` | `boolean` | `false` | Indicates whether the driver supports absolute positioning of a cursor.
`spring.batch.job.jdbccursoritemreader.useSharedExtendedConnection` | `boolean` | `false` | Indicates whether the connection is shared with other processing (and is therefore part of a transaction).
`spring.batch.job.jdbccursoritemreader.sql` | `String` | `null` | SQL query from which to read.

See the `JdbcCursorItemReader` documentation.

### KafkaItemReader

Ingesting a partition of data from a Kafka topic is useful and exactly what the `KafkaItemReader` can do. To configure a `KafkaItemReader`, two pieces of configuration are required. First, configuring Kafka with Spring Boot’s Kafka autoconfiguration is required (see the Spring Boot Kafka documentation). Once you have configured the Kafka properties from Spring Boot, you can configure the `KafkaItemReader` itself by setting the following properties:

Table 5. `KafkaItemReader` Properties
Property | Type | Default Value | Description
--- | --- | --- | ---
`spring.batch.job.kafkaitemreader.name` | `String` | `null` | Name used to provide unique keys in the `ExecutionContext`.
`spring.batch.job.kafkaitemreader.topic` | `String` | `null` | Name of the topic from which to read.
`spring.batch.job.kafkaitemreader.partitions` | `List<Integer>` | empty list | List of partition indices from which to read.
`spring.batch.job.kafkaitemreader.pollTimeOutInSeconds` | `long` | 30 | Timeout for the `poll()` operations.
`spring.batch.job.kafkaitemreader.saveState` | `boolean` | `true` | Determines whether the state should be saved for restarts.

See the `KafkaItemReader` documentation.

## ItemProcessor Configuration

The single-step batch job autoconfiguration accepts an `ItemProcessor` if one is available within the `ApplicationContext`. If one is found of the correct type (`ItemProcessor<Map<String, Object>, Map<String, Object>>`), it is autowired into the step.

## Autoconfiguration for ItemWriter implementations

This starter provides autoconfiguration for `ItemWriter` implementations that match the supported `ItemReader` implementations: `AmqpItemWriter`, `FlatFileItemWriter`, `JdbcItemWriter`, and `KafkaItemWriter`. This section covers how to use autoconfiguration to configure a supported `ItemWriter`.

### AmqpItemWriter

To write to a RabbitMQ queue, you need two sets of configuration. First, you need an `AmqpTemplate`. The easiest way to get this is by using Spring Boot’s RabbitMQ autoconfiguration. See the Spring Boot RabbitMQ documentation. Once you have configured the `AmqpTemplate`, you can configure the `AmqpItemWriter` by setting the following properties:

Table 6. `AmqpItemWriter` Properties
Property | Type | Default Value | Description
--- | --- | --- | ---
`spring.batch.job.amqpitemwriter.enabled` | `boolean` | `false` | If `true`, the autoconfiguration runs.
`spring.batch.job.amqpitemwriter.jsonConverterEnabled` | `boolean` | `true` | Indicates whether `Jackson2JsonMessageConverter` should be registered to convert messages.

### FlatFileItemWriter

To write a file as the output of the step, you can configure `FlatFileItemWriter`. Autoconfiguration accepts components that have been explicitly configured (such as `LineAggregator`, `FieldExtractor`, `FlatFileHeaderCallback`, or a `FlatFileFooterCallback`) and components that have been configured by setting the following properties specified:

Table 7. `FlatFileItemWriter` Properties
Property | Type | Default Value | Description
--- | --- | --- | ---
`spring.batch.job.flatfileitemwriter.resource` | `Resource` | `null` | The resource to be read.
`spring.batch.job.flatfileitemwriter.delimited` | `boolean` | `false` | Indicates whether the output file is a delimited file. If `true`, `spring.batch.job.flatfileitemwriter.formatted` must be `false`.
`spring.batch.job.flatfileitemwriter.formatted` | `boolean` | `false` | Indicates whether the output file a formatted file. If `true`, `spring.batch.job.flatfileitemwriter.delimited` must be `false`.
`spring.batch.job.flatfileitemwriter.format` | `String` | `null` | The format used to generate the output for a formatted file. The formatting is performed by using `String.format`.
`spring.batch.job.flatfileitemwriter.locale` | `Locale` | `Locale.getDefault()` | The `Locale` to be used when generating the file.
`spring.batch.job.flatfileitemwriter.maximumLength` | `int` | 0 | Max length of the record. If 0, the size is unbounded.
`spring.batch.job.flatfileitemwriter.minimumLength` | `int` | 0 | The minimum record length.
`spring.batch.job.flatfileitemwriter.delimiter` | `String` | `,` | The `String` used to delimit fields in a delimited file.
`spring.batch.job.flatfileitemwriter.encoding` | `String` | `FlatFileItemReader.DEFAULT_CHARSET` | Encoding to use when writing the file.
`spring.batch.job.flatfileitemwriter.forceSync` | `boolean` | `false` | Indicates whether a file should be force-synced to the disk on flush.
`spring.batch.job.flatfileitemwriter.names` | `String []` | `null` | List of names for each field parsed from a record. These names are the keys in the `Map<String, Object>` for the items received by this `ItemWriter`.
`spring.batch.job.flatfileitemwriter.append` | `boolean` | `false` | Indicates whether a file should be appended to if the output file is found.
`spring.batch.job.flatfileitemwriter.lineSeparator` | `String` | `FlatFileItemWriter.DEFAULT_LINE_SEPARATOR` | What `String` to use to separate lines in the output file.
`spring.batch.job.flatfileitemwriter.name` | `String` | `null` | Name used to provide unique keys in the `ExecutionContext`.
`spring.batch.job.flatfileitemwriter.saveState` | `boolean` | `true` | Determines whether the state should be saved for restarts.
`spring.batch.job.flatfileitemwriter.shouldDeleteIfEmpty` | `boolean` | `false` | If set to `true`, an empty file (there is no output) is deleted when the job completes.
`spring.batch.job.flatfileitemwriter.shouldDeleteIfExists` | `boolean` | `true` | If set to `true` and a file is found where the output file should be, it is deleted before the step begins.
`spring.batch.job.flatfileitemwriter.transactional` | `boolean` | `FlatFileItemWriter.DEFAULT_TRANSACTIONAL` | Indicates whether the reader is a transactional queue (indicating that the items read are returned to the queue upon a failure).

See the `FlatFileItemWriter` documentation.

### JdbcBatchItemWriter

To write the output of a step to a relational database, this starter provides the ability to autoconfigure a `JdbcBatchItemWriter`. The autoconfiguration lets you provide your own `ItemPreparedStatementSetter` or `ItemSqlParameterSourceProvider` and configuration options by setting the following properties:

Table 8. `JdbcBatchItemWriter` Properties
Property | Type | Default Value | Description
--- | --- | --- | ---
`spring.batch.job.jdbcbatchitemwriter.name` | `String` | `null` | Name used to provide unique keys in the `ExecutionContext`.
`spring.batch.job.jdbcbatchitemwriter.sql` | `String` | `null` | The SQL used to insert each item.
`spring.batch.job.jdbcbatchitemwriter.assertUpdates` | `boolean` | `true` | Whether to verify that every insert results in the update of at least one record.

See the `JdbcBatchItemWriter` documentation.

### KafkaItemWriter

To write step output to a Kafka topic, you need `KafkaItemWriter`. This starter provides autoconfiguration for a `KafkaItemWriter` by using facilities from two places. The first is Spring Boot’s Kafka autoconfiguration. (See the Spring Boot Kafka documentation.) Second, this starter lets you configure two properties on the writer.

Table 9. `KafkaItemWriter` Properties
Property | Type | Default Value | Description
--- | --- | --- | ---
`spring.batch.job.kafkaitemwriter.topic` | `String` | `null` | The Kafka topic to which to write.
`spring.batch.job.kafkaitemwriter.delete` | `boolean` | `false` | Whether the items being passed to the writer are all to be sent as delete events to the topic.

For more about the configuration options for the `KafkaItemWriter`, see the `KafkaItemWiter` documentation.