## Configuring a `Step`

XML Java Both

As discussed in the domain chapter, a `Step` is a domain object that encapsulates an independent, sequential phase of a batch job and contains all of the information necessary to define and control the actual batch processing. This is a necessarily vague description because the contents of any given `Step` are at the discretion of the developer writing a `Job`. A `Step` can be as simple or complex as the developer desires. A simple `Step` might load data from a file into the database, requiring little or no code (depending upon the implementations used). A more complex `Step` might have complicated business rules that are applied as part of the processing, as shown in the following image:

Figure 1. Step

### Chunk-oriented Processing

Spring Batch uses a 'Chunk-oriented' processing style within its most common implementation. Chunk oriented processing refers to reading the data one at a time and creating 'chunks' that are written out within a transaction boundary. Once the number of items read equals the commit interval, the entire chunk is written out by the `ItemWriter`, and then the transaction is committed. The following image shows the process:

Figure 2. Chunk-oriented Processing

The following pseudo code shows the same concepts in a simplified form:

    List items = new Arraylist();
    for(int i = 0; i < commitInterval; i++){
        Object item = itemReader.read();
        if (item != null) {
            items.add(item);
        }
    }
    itemWriter.write(items);

A chunk-oriented step can also be configured with an optional `ItemProcessor` to process items before passing them to the `ItemWriter`. The following image shows the process when an `ItemProcessor` is registered in the step:

Figure 3. Chunk-oriented Processing with Item Processor

The following pseudo code shows how this is implemented in a simplified form:

    List items = new Arraylist();
    for(int i = 0; i < commitInterval; i++){
        Object item = itemReader.read();
        if (item != null) {
            items.add(item);
        }
    }

    List processedItems = new Arraylist();
    for(Object item: items){
        Object processedItem = itemProcessor.process(item);
        if (processedItem != null) {
            processedItems.add(processedItem);
        }
    }

    itemWriter.write(processedItems);

For more details about item processors and their use cases, please refer to the Item processing section.

#### Configuring a `Step`

Despite the relatively short list of required dependencies for a `Step`, it is an extremely complex class that can potentially contain many collaborators.

In order to ease configuration, the Spring Batch XML namespace can be used, as shown in the following example:

XML Configuration

    <job id="sampleJob" job-repository="jobRepository">
        <step id="step1">
            <tasklet transaction-manager="transactionManager">
                <chunk reader="itemReader" writer="itemWriter" commit-interval="10"/>
            </tasklet>
        </step>
    </job>

When using Java configuration, the Spring Batch builders can be used, as shown in the following example:

Java Configuration

    /**
     * Note the JobRepository is typically autowired in and not needed to be explicitly
     * configured
     */
    @Bean
    public Job sampleJob(JobRepository jobRepository, Step sampleStep) {
        return this.jobBuilderFactory.get("sampleJob")
        			.repository(jobRepository)
                    .start(sampleStep)
                    .build();
    }

    /**
     * Note the TransactionManager is typically autowired in and not needed to be explicitly
     * configured
     */
    @Bean
    public Step sampleStep(PlatformTransactionManager transactionManager) {
    	return this.stepBuilderFactory.get("sampleStep")
    				.transactionManager(transactionManager)
    				.<String, String>chunk(10)
    				.reader(itemReader())
    				.writer(itemWriter())
    				.build();
    }

The configuration above includes the only required dependencies to create a item-oriented step:

- `reader`: The `ItemReader` that provides items for processing.

- `writer`: The `ItemWriter` that processes the items provided by the `ItemReader`.

- `transaction-manager`: Spring’s `PlatformTransactionManager` that begins and commits transactions during processing.

- `transactionManager`: Spring’s `PlatformTransactionManager` that begins and commits transactions during processing.

- `job-repository`: The XML-specific name of the `JobRepository` that periodically stores the `StepExecution` and `ExecutionContext` during processing (just before committing). For an in-line `<step/>` (one defined within a `<job/>`), it is an attribute on the `<job/>` element. For a standalone `<step/>`, it is defined as an attribute of the <tasklet/>.

- `repository`: The Java-specific name of the `JobRepository` that periodically stores the `StepExecution` and `ExecutionContext` during processing (just before committing).

- `commit-interval`: The XML-specific name of the number of items to be processed before the transaction is committed.

- `chunk`: The Java-specific name of the dependency that indicates that this is an item-based step and the number of items to be processed before the transaction is committed.

It should be noted that `job-repository` defaults to `jobRepository` and `transaction-manager` defaults to `transactionManager`. Also, the `ItemProcessor` is optional, since the item could be directly passed from the reader to the writer.

It should be noted that `repository` defaults to `jobRepository` and `transactionManager` defaults to `transactionManager` (all provided through the infrastructure from `@EnableBatchProcessing`). Also, the `ItemProcessor` is optional, since the item could be directly passed from the reader to the writer.

#### Inheriting from a Parent `Step`

If a group of `Steps` share similar configurations, then it may be helpful to define a "parent" `Step` from which the concrete `Steps` may inherit properties. Similar to class inheritance in Java, the "child" `Step` combines its elements and attributes with the parent’s. The child also overrides any of the parent’s `Steps`.

In the following example, the `Step`, "concreteStep1", inherits from "parentStep". It is instantiated with 'itemReader', 'itemProcessor', 'itemWriter', `startLimit=5`, and `allowStartIfComplete=true`. Additionally, the `commitInterval` is '5', since it is overridden by the "concreteStep1" `Step`, as shown in the following example:

    <step id="parentStep">
        <tasklet allow-start-if-complete="true">
            <chunk reader="itemReader" writer="itemWriter" commit-interval="10"/>
        </tasklet>
    </step>

    <step id="concreteStep1" parent="parentStep">
        <tasklet start-limit="5">
            <chunk processor="itemProcessor" commit-interval="5"/>
        </tasklet>
    </step>

The `id` attribute is still required on the step within the job element. This is for two reasons:

- The `id` is used as the step name when persisting the `StepExecution`. If the same standalone step is referenced in more than one step in the job, an error occurs.

- When creating job flows, as described later in this chapter, the `next` attribute should be referring to the step in the flow, not the standalone step.

##### Abstract `Step`

Sometimes, it may be necessary to define a parent `Step` that is not a complete `Step` configuration. If, for instance, the `reader`, `writer`, and `tasklet` attributes are left off of a `Step` configuration, then initialization fails. If a parent must be defined without these properties, then the `abstract` attribute should be used. An `abstract` `Step` is only extended, never instantiated.

In the following example, the `Step` `abstractParentStep` would not be instantiated if it were not declared to be abstract. The `Step`, "concreteStep2", has 'itemReader', 'itemWriter', and commit-interval=10.

    <step id="abstractParentStep" abstract="true">
        <tasklet>
            <chunk commit-interval="10"/>
        </tasklet>
    </step>

    <step id="concreteStep2" parent="abstractParentStep">
        <tasklet>
            <chunk reader="itemReader" writer="itemWriter"/>
        </tasklet>
    </step>

##### Merging Lists

Some of the configurable elements on `Steps` are lists, such as the `<listeners/>` element. If both the parent and child `Steps` declare a `<listeners/>` element, then the child’s list overrides the parent’s. In order to allow a child to add additional listeners to the list defined by the parent, every list element has a `merge` attribute. If the element specifies that `merge="true"`, then the child’s list is combined with the parent’s instead of overriding it.

In the following example, the `Step` "concreteStep3", is created with two listeners: `listenerOne` and `listenerTwo`:

    <step id="listenersParentStep" abstract="true">
        <listeners>
            <listener ref="listenerOne"/>
        <listeners>
    </step>

    <step id="concreteStep3" parent="listenersParentStep">
        <tasklet>
            <chunk reader="itemReader" writer="itemWriter" commit-interval="5"/>
        </tasklet>
        <listeners merge="true">
            <listener ref="listenerTwo"/>
        <listeners>
    </step>

#### The Commit Interval

As mentioned previously, a step reads in and writes out items, periodically committing using the supplied `PlatformTransactionManager`. With a `commit-interval` of 1, it commits after writing each individual item. This is less than ideal in many situations, since beginning and committing a transaction is expensive. Ideally, it is preferable to process as many items as possible in each transaction, which is completely dependent upon the type of data being processed and the resources with which the step is interacting. For this reason, the number of items that are processed within a commit can be configured.

The following example shows a `step` whose `tasklet` has a `commit-interval` value of 10 as it would be defined in XML:

XML Configuration

    <job id="sampleJob">
        <step id="step1">
            <tasklet>
                <chunk reader="itemReader" writer="itemWriter" commit-interval="10"/>
            </tasklet>
        </step>
    </job>

The following example shows a `step` whose `tasklet` has a `commit-interval` value of 10 as it would be defined in Java:

Java Configuration

    @Bean
    public Job sampleJob() {
        return this.jobBuilderFactory.get("sampleJob")
                         .start(step1())
                         .build();
    }

    @Bean
    public Step step1() {
    	return this.stepBuilderFactory.get("step1")
    				.<String, String>chunk(10)
    				.reader(itemReader())
    				.writer(itemWriter())
    				.build();
    }

In the preceding example, 10 items are processed within each transaction. At the beginning of processing, a transaction is begun. Also, each time `read` is called on the `ItemReader`, a counter is incremented. When it reaches 10, the list of aggregated items is passed to the `ItemWriter`, and the transaction is committed.

#### Configuring a `Step` for Restart

In the "Configuring and Running a Job" section , restarting a `Job` was discussed. Restart has numerous impacts on steps, and, consequently, may require some specific configuration.

##### Setting a Start Limit

There are many scenarios where you may want to control the number of times a `Step` may be started. For example, a particular `Step` might need to be configured so that it only runs once because it invalidates some resource that must be fixed manually before it can be run again. This is configurable on the step level, since different steps may have different requirements. A `Step` that may only be executed once can exist as part of the same `Job` as a `Step` that can be run infinitely.

The following code fragment shows an example of a start limit configuration in XML:

XML Configuration

    <step id="step1">
        <tasklet start-limit="1">
            <chunk reader="itemReader" writer="itemWriter" commit-interval="10"/>
        </tasklet>
    </step>

The following code fragment shows an example of a start limit configuration in Java:

Java Configuration

    @Bean
    public Step step1() {
    	return this.stepBuilderFactory.get("step1")
    				.<String, String>chunk(10)
    				.reader(itemReader())
    				.writer(itemWriter())
    				.startLimit(1)
    				.build();
    }

The step shown in the preceding example can be run only once. Attempting to run it again causes a `StartLimitExceededException` to be thrown. Note that the default value for the start-limit is `Integer.MAX_VALUE`.

##### Restarting a Completed `Step`

In the case of a restartable job, there may be one or more steps that should always be run, regardless of whether or not they were successful the first time. An example might be a validation step or a `Step` that cleans up resources before processing. During normal processing of a restarted job, any step with a status of 'COMPLETED', meaning it has already been completed successfully, is skipped. Setting `allow-start-if-complete` to "true" overrides this so that the step always runs.

The following code fragment shows how to define a restartable job in XML:

XML Configuration

    <step id="step1">
        <tasklet allow-start-if-complete="true">
            <chunk reader="itemReader" writer="itemWriter" commit-interval="10"/>
        </tasklet>
    </step>

The following code fragment shows how to define a restartable job in Java:

Java Configuration

    @Bean
    public Step step1() {
    	return this.stepBuilderFactory.get("step1")
    				.<String, String>chunk(10)
    				.reader(itemReader())
    				.writer(itemWriter())
    				.allowStartIfComplete(true)
    				.build();
    }

##### `Step` Restart Configuration Example

The following XML example shows how to configure a job to have steps that can be restarted:

XML Configuration

    <job id="footballJob" restartable="true">
        <step id="playerload" next="gameLoad">
            <tasklet>
                <chunk reader="playerFileItemReader" writer="playerWriter"
                       commit-interval="10" />
            </tasklet>
        </step>
        <step id="gameLoad" next="playerSummarization">
            <tasklet allow-start-if-complete="true">
                <chunk reader="gameFileItemReader" writer="gameWriter"
                       commit-interval="10"/>
            </tasklet>
        </step>
        <step id="playerSummarization">
            <tasklet start-limit="2">
                <chunk reader="playerSummarizationSource" writer="summaryWriter"
                       commit-interval="10"/>
            </tasklet>
        </step>
    </job>

The following Java example shows how to configure a job to have steps that can be restarted:

Java Configuration

    @Bean
    public Job footballJob() {
    	return this.jobBuilderFactory.get("footballJob")
    				.start(playerLoad())
    				.next(gameLoad())
    				.next(playerSummarization())
    				.build();
    }

    @Bean
    public Step playerLoad() {
    	return this.stepBuilderFactory.get("playerLoad")
    			.<String, String>chunk(10)
    			.reader(playerFileItemReader())
    			.writer(playerWriter())
    			.build();
    }

    @Bean
    public Step gameLoad() {
    	return this.stepBuilderFactory.get("gameLoad")
    			.allowStartIfComplete(true)
    			.<String, String>chunk(10)
    			.reader(gameFileItemReader())
    			.writer(gameWriter())
    			.build();
    }

    @Bean
    public Step playerSummarization() {
    	return this.stepBuilderFactory.get("playerSummarization")
    			.startLimit(2)
    			.<String, String>chunk(10)
    			.reader(playerSummarizationSource())
    			.writer(summaryWriter())
    			.build();
    }

The preceding example configuration is for a job that loads in information about football games and summarizes them. It contains three steps: `playerLoad`, `gameLoad`, and `playerSummarization`. The `playerLoad` step loads player information from a flat file, while the `gameLoad` step does the same for games. The final step, `playerSummarization`, then summarizes the statistics for each player, based upon the provided games. It is assumed that the file loaded by `playerLoad` must be loaded only once, but that `gameLoad` can load any games found within a particular directory, deleting them after they have been successfully loaded into the database. As a result, the `playerLoad` step contains no additional configuration. It can be started any number of times, and, if complete, is skipped. The `gameLoad` step, however, needs to be run every time in case extra files have been added since it last ran. It has 'allow-start-if-complete' set to 'true' in order to always be started. (It is assumed that the database table games are loaded into has a process indicator on it, to ensure new games can be properly found by the summarization step). The summarization step, which is the most important in the job, is configured to have a start limit of 2. This is useful because if the step continually fails, a new exit code is returned to the operators that control job execution, and it can not start again until manual intervention has taken place.

| This job provides an example for this document and is not the same as the `footballJob` found in the samples project.

The remainder of this section describes what happens for each of the three runs of the `footballJob` example.

Run 1:

1. `playerLoad` runs and completes successfully, adding 400 players to the 'PLAYERS' table.

2. `gameLoad` runs and processes 11 files worth of game data, loading their contents into the 'GAMES' table.

3. `playerSummarization` begins processing and fails after 5 minutes.

Run 2:

1. `playerLoad` does not run, since it has already completed successfully, and `allow-start-if-complete` is 'false' (the default).

2. `gameLoad` runs again and processes another 2 files, loading their contents into the 'GAMES' table as well (with a process indicator indicating they have yet to be processed).

3. `playerSummarization` begins processing of all remaining game data (filtering using the process indicator) and fails again after 30 minutes.

Run 3:

1. `playerLoad` does not run, since it has already completed successfully, and `allow-start-if-complete` is 'false' (the default).

2. `gameLoad` runs again and processes another 2 files, loading their contents into the 'GAMES' table as well (with a process indicator indicating they have yet to be processed).

3. `playerSummarization` is not started and the job is immediately killed, since this is the third execution of `playerSummarization`, and its limit is only 2. Either the limit must be raised or the `Job` must be executed as a new `JobInstance`.

#### Configuring Skip Logic

There are many scenarios where errors encountered while processing should not result in `Step` failure, but should be skipped instead. This is usually a decision that must be made by someone who understands the data itself and what meaning it has. Financial data, for example, may not be skippable because it results in money being transferred, which needs to be completely accurate. Loading a list of vendors, on the other hand, might allow for skips. If a vendor is not loaded because it was formatted incorrectly or was missing necessary information, then there probably are not issues. Usually, these bad records are logged as well, which is covered later when discussing listeners.

The following XML example shows an example of using a skip limit:

XML Configuration

    <step id="step1">
       <tasklet>
          <chunk reader="flatFileItemReader" writer="itemWriter"
                 commit-interval="10" skip-limit="10">
             <skippable-exception-classes>
                <include class="org.springframework.batch.item.file.FlatFileParseException"/>
             </skippable-exception-classes>
          </chunk>
       </tasklet>
    </step>

The following Java example shows an example of using a skip limit:

Java Configuration

    @Bean
    public Step step1() {
    	return this.stepBuilderFactory.get("step1")
    				.<String, String>chunk(10)
    				.reader(flatFileItemReader())
    				.writer(itemWriter())
    				.faultTolerant()
    				.skipLimit(10)
    				.skip(FlatFileParseException.class)
    				.build();
    }

In the preceding example, a `FlatFileItemReader` is used. If, at any point, a `FlatFileParseException` is thrown, the item is skipped and counted against the total skip limit of 10. Exceptions (and their subclasses) that are declared might be thrown during any phase of the chunk processing (read, process, write) but separate counts are made of skips on read, process, and write inside the step execution, but the limit applies across all skips. Once the skip limit is reached, the next exception found causes the step to fail. In other words, the eleventh skip triggers the exception, not the tenth.

One problem with the preceding example is that any other exception besides a `FlatFileParseException` causes the `Job` to fail. In certain scenarios, this may be the correct behavior. However, in other scenarios, it may be easier to identify which exceptions should cause failure and skip everything else.

The following XML example shows an example excluding a particular exception:

XML Configuration

    <step id="step1">
        <tasklet>
            <chunk reader="flatFileItemReader" writer="itemWriter"
                   commit-interval="10" skip-limit="10">
                <skippable-exception-classes>
                    <include class="java.lang.Exception"/>
                    <exclude class="java.io.FileNotFoundException"/>
                </skippable-exception-classes>
            </chunk>
        </tasklet>
    </step>

The following Java example shows an example excluding a particular exception:

Java Configuration

    @Bean
    public Step step1() {
    	return this.stepBuilderFactory.get("step1")
    				.<String, String>chunk(10)
    				.reader(flatFileItemReader())
    				.writer(itemWriter())
    				.faultTolerant()
    				.skipLimit(10)
    				.skip(Exception.class)
    				.noSkip(FileNotFoundException.class)
    				.build();
    }

By identifying `java.lang.Exception` as a skippable exception class, the configuration indicates that all `Exceptions` are skippable. However, by 'excluding' `java.io.FileNotFoundException`, the configuration refines the list of skippable exception classes to be all `Exceptions` except `FileNotFoundException`. Any excluded exception classes is fatal if encountered (that is, they are not skipped).

For any exception encountered, the skippability is determined by the nearest superclass in the class hierarchy. Any unclassified exception is treated as 'fatal'.

The order of the `<include/>` and `<exclude/>` elements does not matter.

The order of the `skip` and `noSkip` method calls does not matter.

#### Configuring Retry Logic

In most cases, you want an exception to cause either a skip or a `Step` failure. However, not all exceptions are deterministic. If a `FlatFileParseException` is encountered while reading, it is always thrown for that record. Resetting the `ItemReader` does not help. However, for other exceptions, such as a `DeadlockLoserDataAccessException`, which indicates that the current process has attempted to update a record that another process holds a lock on. Waiting and trying again might result in success.

In XML, retry should be configured as follows:

    <step id="step1">
       <tasklet>
          <chunk reader="itemReader" writer="itemWriter"
                 commit-interval="2" retry-limit="3">
             <retryable-exception-classes>
                <include class="org.springframework.dao.DeadlockLoserDataAccessException"/>
             </retryable-exception-classes>
          </chunk>
       </tasklet>
    </step>

In Java, retry should be configured as follows:

    @Bean
    public Step step1() {
    	return this.stepBuilderFactory.get("step1")
    				.<String, String>chunk(2)
    				.reader(itemReader())
    				.writer(itemWriter())
    				.faultTolerant()
    				.retryLimit(3)
    				.retry(DeadlockLoserDataAccessException.class)
    				.build();
    }

The `Step` allows a limit for the number of times an individual item can be retried and a list of exceptions that are 'retryable'. More details on how retry works can be found in retry.

#### Controlling Rollback

By default, regardless of retry or skip, any exceptions thrown from the `ItemWriter` cause the transaction controlled by the `Step` to rollback. If skip is configured as described earlier, exceptions thrown from the `ItemReader` do not cause a rollback. However, there are many scenarios in which exceptions thrown from the `ItemWriter` should not cause a rollback, because no action has taken place to invalidate the transaction. For this reason, the `Step` can be configured with a list of exceptions that should not cause rollback.

In XML, you can control rollback as follows:

XML Configuration

    <step id="step1">
       <tasklet>
          <chunk reader="itemReader" writer="itemWriter" commit-interval="2"/>
          <no-rollback-exception-classes>
             <include class="org.springframework.batch.item.validator.ValidationException"/>
          </no-rollback-exception-classes>
       </tasklet>
    </step>

In Java, you can control rollback as follows:

Java Configuration

    @Bean
    public Step step1() {
    	return this.stepBuilderFactory.get("step1")
    				.<String, String>chunk(2)
    				.reader(itemReader())
    				.writer(itemWriter())
    				.faultTolerant()
    				.noRollback(ValidationException.class)
    				.build();
    }

##### Transactional Readers

The basic contract of the `ItemReader` is that it is forward only. The step buffers reader input, so that in the case of a rollback, the items do not need to be re-read from the reader. However, there are certain scenarios in which the reader is built on top of a transactional resource, such as a JMS queue. In this case, since the queue is tied to the transaction that is rolled back, the messages that have been pulled from the queue are put back on. For this reason, the step can be configured to not buffer the items.

The following example shows how to create reader that does not buffer items in XML:

XML Configuration

    <step id="step1">
        <tasklet>
            <chunk reader="itemReader" writer="itemWriter" commit-interval="2"
                   is-reader-transactional-queue="true"/>
        </tasklet>
    </step>

The following example shows how to create reader that does not buffer items in Java:

Java Configuration

    @Bean
    public Step step1() {
    	return this.stepBuilderFactory.get("step1")
    				.<String, String>chunk(2)
    				.reader(itemReader())
    				.writer(itemWriter())
    				.readerIsTransactionalQueue()
    				.build();
    }

#### Transaction Attributes

Transaction attributes can be used to control the `isolation`, `propagation`, and `timeout` settings. More information on setting transaction attributes can be found in the Spring core documentation.

The following example sets the `isolation`, `propagation`, and `timeout` transaction attributes in XML:

XML Configuration

    <step id="step1">
        <tasklet>
            <chunk reader="itemReader" writer="itemWriter" commit-interval="2"/>
            <transaction-attributes isolation="DEFAULT"
                                    propagation="REQUIRED"
                                    timeout="30"/>
        </tasklet>
    </step>

The following example sets the `isolation`, `propagation`, and `timeout` transaction attributes in Java:

Java Configuration

    @Bean
    public Step step1() {
    	DefaultTransactionAttribute attribute = new DefaultTransactionAttribute();
    	attribute.setPropagationBehavior(Propagation.REQUIRED.value());
    	attribute.setIsolationLevel(Isolation.DEFAULT.value());
    	attribute.setTimeout(30);

    	return this.stepBuilderFactory.get("step1")
    				.<String, String>chunk(2)
    				.reader(itemReader())
    				.writer(itemWriter())
    				.transactionAttribute(attribute)
    				.build();
    }

#### Registering `ItemStream` with a `Step`

The step has to take care of `ItemStream` callbacks at the necessary points in its lifecycle (For more information on the `ItemStream` interface, see ItemStream). This is vital if a step fails and might need to be restarted, because the `ItemStream` interface is where the step gets the information it needs about persistent state between executions.

If the `ItemReader`, `ItemProcessor`, or `ItemWriter` itself implements the `ItemStream` interface, then these are registered automatically. Any other streams need to be registered separately. This is often the case where indirect dependencies, such as delegates, are injected into the reader and writer. A stream can be registered on the `step` through the 'stream' element.

The following example shows how to register a `stream` on a `step` in XML:

XML Configuration

    <step id="step1">
        <tasklet>
            <chunk reader="itemReader" writer="compositeWriter" commit-interval="2">
                <streams>
                    <stream ref="fileItemWriter1"/>
                    <stream ref="fileItemWriter2"/>
                </streams>
            </chunk>
        </tasklet>
    </step>

    <beans:bean id="compositeWriter"
                class="org.springframework.batch.item.support.CompositeItemWriter">
        <beans:property name="delegates">
            <beans:list>
                <beans:ref bean="fileItemWriter1" />
                <beans:ref bean="fileItemWriter2" />
            </beans:list>
        </beans:property>
    </beans:bean>

The following example shows how to register a `stream` on a `step` in Java:

Java Configuration

    @Bean
    public Step step1() {
    	return this.stepBuilderFactory.get("step1")
    				.<String, String>chunk(2)
    				.reader(itemReader())
    				.writer(compositeItemWriter())
    				.stream(fileItemWriter1())
    				.stream(fileItemWriter2())
    				.build();
    }

    /**
     * In Spring Batch 4, the CompositeItemWriter implements ItemStream so this isn't
     * necessary, but used for an example.
     */
    @Bean
    public CompositeItemWriter compositeItemWriter() {
    	List<ItemWriter> writers = new ArrayList<>(2);
    	writers.add(fileItemWriter1());
    	writers.add(fileItemWriter2());

    	CompositeItemWriter itemWriter = new CompositeItemWriter();

    	itemWriter.setDelegates(writers);

    	return itemWriter;
    }

In the example above, the `CompositeItemWriter` is not an `ItemStream`, but both of its delegates are. Therefore, both delegate writers must be explicitly registered as streams in order for the framework to handle them correctly. The `ItemReader` does not need to be explicitly registered as a stream because it is a direct property of the `Step`. The step is now restartable, and the state of the reader and writer is correctly persisted in the event of a failure.

#### Intercepting `Step` Execution

Just as with the `Job`, there are many events during the execution of a `Step` where a user may need to perform some functionality. For example, in order to write out to a flat file that requires a footer, the `ItemWriter` needs to be notified when the `Step` has been completed, so that the footer can be written. This can be accomplished with one of many `Step` scoped listeners.

Any class that implements one of the extensions of `StepListener` (but not that interface itself since it is empty) can be applied to a step through the `listeners` element. The `listeners` element is valid inside a step, tasklet, or chunk declaration. It is recommended that you declare the listeners at the level at which its function applies, or, if it is multi-featured (such as `StepExecutionListener` and `ItemReadListener`), then declare it at the most granular level where it applies.

The following example shows a listener applied at the chunk level in XML:

XML Configuration

    <step id="step1">
        <tasklet>
            <chunk reader="reader" writer="writer" commit-interval="10"/>
            <listeners>
                <listener ref="chunkListener"/>
            </listeners>
        </tasklet>
    </step>

The following example shows a listener applied at the chunk level in Java:

Java Configuration

    @Bean
    public Step step1() {
    	return this.stepBuilderFactory.get("step1")
    				.<String, String>chunk(10)
    				.reader(reader())
    				.writer(writer())
    				.listener(chunkListener())
    				.build();
    }

An `ItemReader`, `ItemWriter` or `ItemProcessor` that itself implements one of the `StepListener` interfaces is registered automatically with the `Step` if using the namespace `<step>` element or one of the `*StepFactoryBean` factories. This only applies to components directly injected into the `Step`. If the listener is nested inside another component, it needs to be explicitly registered (as described previously under Registering `ItemStream` with a `Step`).

In addition to the `StepListener` interfaces, annotations are provided to address the same concerns. Plain old Java objects can have methods with these annotations that are then converted into the corresponding `StepListener` type. It is also common to annotate custom implementations of chunk components such as `ItemReader` or `ItemWriter` or `Tasklet`. The annotations are analyzed by the XML parser for the `<listener/>` elements as well as registered with the `listener` methods in the builders, so all you need to do is use the XML namespace or builders to register the listeners with a step.

##### `StepExecutionListener`

`StepExecutionListener` represents the most generic listener for `Step` execution. It allows for notification before a `Step` is started and after it ends, whether it ended normally or failed, as shown in the following example:

    public interface StepExecutionListener extends StepListener {

        void beforeStep(StepExecution stepExecution);

        ExitStatus afterStep(StepExecution stepExecution);

    }

`ExitStatus` is the return type of `afterStep` in order to allow listeners the chance to modify the exit code that is returned upon completion of a `Step`.

The annotations corresponding to this interface are:

- `@BeforeStep`

- `@AfterStep`

##### `ChunkListener`

A chunk is defined as the items processed within the scope of a transaction. Committing a transaction, at each commit interval, commits a 'chunk'. A `ChunkListener` can be used to perform logic before a chunk begins processing or after a chunk has completed successfully, as shown in the following interface definition:

    public interface ChunkListener extends StepListener {

        void beforeChunk(ChunkContext context);
        void afterChunk(ChunkContext context);
        void afterChunkError(ChunkContext context);

    }

The beforeChunk method is called after the transaction is started but before read is called on the `ItemReader`. Conversely, `afterChunk` is called after the chunk has been committed (and not at all if there is a rollback).

The annotations corresponding to this interface are:

- `@BeforeChunk`

- `@AfterChunk`

- `@AfterChunkError`

A `ChunkListener` can be applied when there is no chunk declaration. The `TaskletStep` is responsible for calling the `ChunkListener`, so it applies to a non-item-oriented tasklet as well (it is called before and after the tasklet).

##### `ItemReadListener`

When discussing skip logic previously, it was mentioned that it may be beneficial to log the skipped records, so that they can be dealt with later. In the case of read errors, this can be done with an `ItemReaderListener`, as shown in the following interface definition:

    public interface ItemReadListener<T> extends StepListener {

        void beforeRead();
        void afterRead(T item);
        void onReadError(Exception ex);

    }

The `beforeRead` method is called before each call to read on the `ItemReader`. The `afterRead` method is called after each successful call to read and is passed the item that was read. If there was an error while reading, the `onReadError` method is called. The exception encountered is provided so that it can be logged.

The annotations corresponding to this interface are:

- `@BeforeRead`

- `@AfterRead`

- `@OnReadError`

##### `ItemProcessListener`

Just as with the `ItemReadListener`, the processing of an item can be 'listened' to, as shown in the following interface definition:

    public interface ItemProcessListener<T, S> extends StepListener {

        void beforeProcess(T item);
        void afterProcess(T item, S result);
        void onProcessError(T item, Exception e);

    }

The `beforeProcess` method is called before `process` on the `ItemProcessor` and is handed the item that is to be processed. The `afterProcess` method is called after the item has been successfully processed. If there was an error while processing, the `onProcessError` method is called. The exception encountered and the item that was attempted to be processed are provided, so that they can be logged.

The annotations corresponding to this interface are:

- `@BeforeProcess`

- `@AfterProcess`

- `@OnProcessError`

##### `ItemWriteListener`

The writing of an item can be 'listened' to with the `ItemWriteListener`, as shown in the following interface definition:

    public interface ItemWriteListener<S> extends StepListener {

        void beforeWrite(List<? extends S> items);
        void afterWrite(List<? extends S> items);
        void onWriteError(Exception exception, List<? extends S> items);

    }

The `beforeWrite` method is called before `write` on the `ItemWriter` and is handed the list of items that is written. The `afterWrite` method is called after the item has been successfully written. If there was an error while writing, the `onWriteError` method is called. The exception encountered and the item that was attempted to be written are provided, so that they can be logged.

The annotations corresponding to this interface are:

- `@BeforeWrite`

- `@AfterWrite`

- `@OnWriteError`

##### `SkipListener`

`ItemReadListener`, `ItemProcessListener`, and `ItemWriteListener` all provide mechanisms for being notified of errors, but none informs you that a record has actually been skipped. `onWriteError`, for example, is called even if an item is retried and successful. For this reason, there is a separate interface for tracking skipped items, as shown in the following interface definition:

    public interface SkipListener<T,S> extends StepListener {

        void onSkipInRead(Throwable t);
        void onSkipInProcess(T item, Throwable t);
        void onSkipInWrite(S item, Throwable t);

    }

`onSkipInRead` is called whenever an item is skipped while reading. It should be noted that rollbacks may cause the same item to be registered as skipped more than once. `onSkipInWrite` is called when an item is skipped while writing. Because the item has been read successfully (and not skipped), it is also provided the item itself as an argument.

The annotations corresponding to this interface are:

- `@OnSkipInRead`

- `@OnSkipInWrite`

- `@OnSkipInProcess`

###### SkipListeners and Transactions

One of the most common use cases for a `SkipListener` is to log out a skipped item, so that another batch process or even human process can be used to evaluate and fix the issue leading to the skip. Because there are many cases in which the original transaction may be rolled back, Spring Batch makes two guarantees:

1. The appropriate skip method (depending on when the error happened) is called only once per item.

2. The `SkipListener` is always called just before the transaction is committed. This is to ensure that any transactional resources call by the listener are not rolled back by a failure within the `ItemWriter`.

### `TaskletStep`

Chunk-oriented processing is not the only way to process in a `Step`. What if a `Step` must consist of a simple stored procedure call? You could implement the call as an `ItemReader` and return null after the procedure finishes. However, doing so is a bit unnatural, since there would need to be a no-op `ItemWriter`. Spring Batch provides the `TaskletStep` for this scenario.

`Tasklet` is a simple interface that has one method, `execute`, which is called repeatedly by the `TaskletStep` until it either returns `RepeatStatus.FINISHED` or throws an exception to signal a failure. Each call to a `Tasklet` is wrapped in a transaction. `Tasklet` implementors might call a stored procedure, a script, or a simple SQL update statement.

To create a `TaskletStep` in XML, the 'ref' attribute of the `<tasklet/>` element should reference a bean that defines a `Tasklet` object. No `<chunk/>` element should be used within the `<tasklet/>`. The following example shows a simple tasklet:

    <step id="step1">
        <tasklet ref="myTasklet"/>
    </step>

To create a `TaskletStep` in Java, the bean passed to the `tasklet` method of the builder should implement the `Tasklet` interface. No call to `chunk` should be called when building a `TaskletStep`. The following example shows a simple tasklet:

    @Bean
    public Step step1() {
        return this.stepBuilderFactory.get("step1")
        			.tasklet(myTasklet())
        			.build();
    }

| `TaskletStep` automatically registers the tasklet as a `StepListener` if it implements the `StepListener` interface.

#### `TaskletAdapter`

As with other adapters for the `ItemReader` and `ItemWriter` interfaces, the `Tasklet` interface contains an implementation that allows for adapting itself to any pre-existing class: `TaskletAdapter`. An example where this may be useful is an existing DAO that is used to update a flag on a set of records. The `TaskletAdapter` can be used to call this class without having to write an adapter for the `Tasklet` interface.

The following example shows how to define a `TaskletAdapter` in XML:

XML Configuration

    <bean id="myTasklet" class="o.s.b.core.step.tasklet.MethodInvokingTaskletAdapter">
        <property name="targetObject">
            <bean class="org.mycompany.FooDao"/>
        </property>
        <property name="targetMethod" value="updateFoo" />
    </bean>

The following example shows how to define a `TaskletAdapter` in Java:

Java Configuration

    @Bean
    public MethodInvokingTaskletAdapter myTasklet() {
    	MethodInvokingTaskletAdapter adapter = new MethodInvokingTaskletAdapter();

    	adapter.setTargetObject(fooDao());
    	adapter.setTargetMethod("updateFoo");

    	return adapter;
    }

#### Example `Tasklet` Implementation

Many batch jobs contain steps that must be done before the main processing begins in order to set up various resources or after processing has completed to cleanup those resources. In the case of a job that works heavily with files, it is often necessary to delete certain files locally after they have been uploaded successfully to another location. The following example (taken from the Spring Batch samples project) is a `Tasklet` implementation with just such a responsibility:

    public class FileDeletingTasklet implements Tasklet, InitializingBean {

        private Resource directory;

        public RepeatStatus execute(StepContribution contribution,
                                    ChunkContext chunkContext) throws Exception {
            File dir = directory.getFile();
            Assert.state(dir.isDirectory());

            File[] files = dir.listFiles();
            for (int i = 0; i < files.length; i++) {
                boolean deleted = files[i].delete();
                if (!deleted) {
                    throw new UnexpectedJobExecutionException("Could not delete file " +
                                                              files[i].getPath());
                }
            }
            return RepeatStatus.FINISHED;
        }

        public void setDirectoryResource(Resource directory) {
            this.directory = directory;
        }

        public void afterPropertiesSet() throws Exception {
            Assert.notNull(directory, "directory must be set");
        }
    }

The preceding `tasklet` implementation deletes all files within a given directory. It should be noted that the `execute` method is called only once. All that is left is to reference the `tasklet` from the `step`.

The following example shows how to reference the `tasklet` from the `step` in XML:

XML Configuration

    <job id="taskletJob">
        <step id="deleteFilesInDir">
           <tasklet ref="fileDeletingTasklet"/>
        </step>
    </job>

    <beans:bean id="fileDeletingTasklet"
                class="org.springframework.batch.sample.tasklet.FileDeletingTasklet">
        <beans:property name="directoryResource">
            <beans:bean id="directory"
                        class="org.springframework.core.io.FileSystemResource">
                <beans:constructor-arg value="target/test-outputs/test-dir" />
            </beans:bean>
        </beans:property>
    </beans:bean>

The following example shows how to reference the `tasklet` from the `step` in Java:

Java Configuration

    @Bean
    public Job taskletJob() {
    	return this.jobBuilderFactory.get("taskletJob")
    				.start(deleteFilesInDir())
    				.build();
    }

    @Bean
    public Step deleteFilesInDir() {
    	return this.stepBuilderFactory.get("deleteFilesInDir")
    				.tasklet(fileDeletingTasklet())
    				.build();
    }

    @Bean
    public FileDeletingTasklet fileDeletingTasklet() {
    	FileDeletingTasklet tasklet = new FileDeletingTasklet();

    	tasklet.setDirectoryResource(new FileSystemResource("target/test-outputs/test-dir"));

    	return tasklet;
    }

### Controlling Step Flow

With the ability to group steps together within an owning job comes the need to be able to control how the job "flows" from one step to another. The failure of a `Step` does not necessarily mean that the `Job` should fail. Furthermore, there may be more than one type of 'success' that determines which `Step` should be executed next. Depending upon how a group of `Steps` is configured, certain steps may not even be processed at all.

#### Sequential Flow

The simplest flow scenario is a job where all of the steps execute sequentially, as shown in the following image:

Figure 4. Sequential Flow

This can be achieved by using the 'next' in a `step`.

The following example shows how to use the `next` attribute in XML:

XML Configuration

    <job id="job">
        <step id="stepA" parent="s1" next="stepB" />
        <step id="stepB" parent="s2" next="stepC"/>
        <step id="stepC" parent="s3" />
    </job>

The following example shows how to use the `next()` method in Java:

Java Configuration

    @Bean
    public Job job() {
    	return this.jobBuilderFactory.get("job")
    				.start(stepA())
    				.next(stepB())
    				.next(stepC())
    				.build();
    }

In the scenario above, 'step A' runs first because it is the first `Step` listed. If 'step A' completes normally, then 'step B' runs, and so on. However, if 'step A' fails, then the entire `Job` fails and 'step B' does not execute.

| With the Spring Batch XML namespace, the first step listed in the configuration is always the first step run by the `Job`. The order of the other step elements does not matter, but the first step must always appear first in the xml.

#### Conditional Flow

In the example above, there are only two possibilities:

1. The `step` is successful and the next `step` should be executed.

2. The `step` failed and, thus, the `job` should fail.

In many cases, this may be sufficient. However, what about a scenario in which the failure of a `step` should trigger a different `step`, rather than causing failure? The following image shows such a flow:

Figure 5. Conditional Flow

In order to handle more complex scenarios, the Spring Batch XML namespace allows transitions elements to be defined within the step element. One such transition is the `next` element. Like the `next` attribute, the `next` element tells the `Job` which `Step` to execute next. However, unlike the attribute, any number of `next` elements are allowed on a given `Step`, and there is no default behavior in the case of failure. This means that, if transition elements are used, then all of the behavior for the `Step` transitions must be defined explicitly. Note also that a single step cannot have both a `next` attribute and a `transition` element.

The `next` element specifies a pattern to match and the step to execute next, as shown in the following example:

XML Configuration

    <job id="job">
        <step id="stepA" parent="s1">
            <next on="*" to="stepB" />
            <next on="FAILED" to="stepC" />
        </step>
        <step id="stepB" parent="s2" next="stepC" />
        <step id="stepC" parent="s3" />
    </job>

The Java API offers a fluent set of methods that let you specify the flow and what to do when a step fails. The following example shows how to specify one step (`stepA`) and then proceed to either of two different steps (`stepB` and `stepC`), depending on whether `stepA` succeeds:

Java Configuration

    @Bean
    public Job job() {
    	return this.jobBuilderFactory.get("job")
    				.start(stepA())
    				.on("*").to(stepB())
    				.from(stepA()).on("FAILED").to(stepC())
    				.end()
    				.build();
    }

When using XML configuration, the `on` attribute of a transition element uses a simple pattern-matching scheme to match the `ExitStatus` that results from the execution of the `Step`.

When using java configuration, the `on()` method uses a simple pattern-matching scheme to match the `ExitStatus` that results from the execution of the `Step`.

Only two special characters are allowed in the pattern:

- "*" matches zero or more characters

- "?" matches exactly one character

For example, "c*t" matches "cat" and "count", while "c?t" matches "cat" but not "count".

While there is no limit to the number of transition elements on a `Step`, if the `Step` execution results in an `ExitStatus` that is not covered by an element, then the framework throws an exception and the `Job` fails. The framework automatically orders transitions from most specific to least specific. This means that, even if the ordering were swapped for "stepA" in the example above, an `ExitStatus` of "FAILED" would still go to "stepC".

##### Batch Status Versus Exit Status

When configuring a `Job` for conditional flow, it is important to understand the difference between `BatchStatus` and `ExitStatus`. `BatchStatus` is an enumeration that is a property of both `JobExecution` and `StepExecution` and is used by the framework to record the status of a `Job` or `Step`. It can be one of the following values: `COMPLETED`, `STARTING`, `STARTED`, `STOPPING`, `STOPPED`, `FAILED`, `ABANDONED`, or `UNKNOWN`. Most of them are self explanatory: `COMPLETED` is the status set when a step or job has completed successfully, `FAILED` is set when it fails, and so on.

The following example contains the 'next' element when using XML configuration:

    <next on="FAILED" to="stepB" />

The following example contains the 'on' element when using Java Configuration:

    ...
    .from(stepA()).on("FAILED").to(stepB())
    ...

At first glance, it would appear that 'on' references the `BatchStatus` of the `Step` to which it belongs. However, it actually references the `ExitStatus` of the `Step`. As the name implies, `ExitStatus` represents the status of a `Step` after it finishes execution.

More specifically, when using XML configuration, the 'next' element shown in the preceding XML configuration example references the exit code of `ExitStatus`.

When using Java configuration, the 'on()' method shown in the preceding Java configuration example references the exit code of `ExitStatus`.

In English, it says: "go to stepB if the exit code is `FAILED` ". By default, the exit code is always the same as the `BatchStatus` for the `Step`, which is why the entry above works. However, what if the exit code needs to be different? A good example comes from the skip sample job within the samples project:

The following example shows how to work with a different exit code in XML:

XML Configuration

    <step id="step1" parent="s1">
        <end on="FAILED" />
        <next on="COMPLETED WITH SKIPS" to="errorPrint1" />
        <next on="*" to="step2" />
    </step>

The following example shows how to work with a different exit code in Java:

Java Configuration

    @Bean
    public Job job() {
    	return this.jobBuilderFactory.get("job")
    			.start(step1()).on("FAILED").end()
    			.from(step1()).on("COMPLETED WITH SKIPS").to(errorPrint1())
    			.from(step1()).on("*").to(step2())
    			.end()
    			.build();
    }

`step1` has three possibilities:

1. The `Step` failed, in which case the job should fail.

2. The `Step` completed successfully.

3. The `Step` completed successfully but with an exit code of 'COMPLETED WITH SKIPS'. In this case, a different step should be run to handle the errors.

The preceding configuration works. However, something needs to change the exit code based on the condition of the execution having skipped records, as shown in the following example:

    public class SkipCheckingListener extends StepExecutionListenerSupport {
        public ExitStatus afterStep(StepExecution stepExecution) {
            String exitCode = stepExecution.getExitStatus().getExitCode();
            if (!exitCode.equals(ExitStatus.FAILED.getExitCode()) &&
                  stepExecution.getSkipCount() > 0) {
                return new ExitStatus("COMPLETED WITH SKIPS");
            }
            else {
                return null;
            }
        }
    }

The above code is a `StepExecutionListener` that first checks to make sure the `Step` was successful and then checks to see if the skip count on the `StepExecution` is higher than 0. If both conditions are met, a new `ExitStatus` with an exit code of `COMPLETED WITH SKIPS` is returned.

#### Configuring for Stop

After the discussion of BatchStatus and ExitStatus, one might wonder how the `BatchStatus` and `ExitStatus` are determined for the `Job`. While these statuses are determined for the `Step` by the code that is executed, the statuses for the `Job` are determined based on the configuration.

So far, all of the job configurations discussed have had at least one final `Step` with no transitions.

In the following XML example, after the `step` executes, the `Job` ends:

    <step id="stepC" parent="s3"/>

In the following Java example, after the `step` executes, the `Job` ends:

    @Bean
    public Job job() {
    	return this.jobBuilderFactory.get("job")
    				.start(step1())
    				.build();
    }

If no transitions are defined for a `Step`, then the status of the `Job` is defined as follows:

- If the `Step` ends with `ExitStatus` FAILED, then the `BatchStatus` and `ExitStatus` of the `Job` are both `FAILED`.

- Otherwise, the `BatchStatus` and `ExitStatus` of the `Job` are both `COMPLETED`.

While this method of terminating a batch job is sufficient for some batch jobs, such as a simple sequential step job, custom defined job-stopping scenarios may be required. For this purpose, Spring Batch provides three transition elements to stop a `Job` (in addition to the `next` element that we discussed previously). Each of these stopping elements stops a `Job` with a particular `BatchStatus`. It is important to note that the stop transition elements have no effect on either the `BatchStatus` or `ExitStatus` of any `Steps` in the `Job`. These elements affect only the final statuses of the `Job`. For example, it is possible for every step in a job to have a status of `FAILED` but for the job to have a status of `COMPLETED`.

##### Ending at a Step

Configuring a step end instructs a `Job` to stop with a `BatchStatus` of `COMPLETED`. A `Job` that has finished with status `COMPLETED` cannot be restarted (the framework throws a `JobInstanceAlreadyCompleteException`).

When using XML configuration, the 'end' element is used for this task. The `end` element also allows for an optional 'exit-code' attribute that can be used to customize the `ExitStatus` of the `Job`. If no 'exit-code' attribute is given, then the `ExitStatus` is `COMPLETED` by default, to match the `BatchStatus`.

When using Java configuration, the 'end' method is used for this task. The `end` method also allows for an optional 'exitStatus' parameter that can be used to customize the `ExitStatus` of the `Job`. If no 'exitStatus' value is provided, then the `ExitStatus` is `COMPLETED` by default, to match the `BatchStatus`.

Consider the following scenario: if `step2` fails, then the `Job` stops with a `BatchStatus` of `COMPLETED` and an `ExitStatus` of `COMPLETED` and `step3` does not run. Otherwise, execution moves to `step3`. Note that if `step2` fails, the `Job` is not restartable (because the status is `COMPLETED`).

The following example shows the scenario in XML:

    <step id="step1" parent="s1" next="step2">

    <step id="step2" parent="s2">
        <end on="FAILED"/>
        <next on="*" to="step3"/>
    </step>

    <step id="step3" parent="s3">

The following example shows the scenario in Java:

    @Bean
    public Job job() {
    	return this.jobBuilderFactory.get("job")
    				.start(step1())
    				.next(step2())
    				.on("FAILED").end()
    				.from(step2()).on("*").to(step3())
    				.end()
    				.build();
    }

##### Failing a Step

Configuring a step to fail at a given point instructs a `Job` to stop with a `BatchStatus` of `FAILED`. Unlike end, the failure of a `Job` does not prevent the `Job` from being restarted.

When using XML configuration, the 'fail' element also allows for an optional 'exit-code' attribute that can be used to customize the `ExitStatus` of the `Job`. If no 'exit-code' attribute is given, then the `ExitStatus` is `FAILED` by default, to match the `BatchStatus`.

Consider the following scenario if `step2` fails, then the `Job` stops with a `BatchStatus` of `FAILED` and an `ExitStatus` of `EARLY TERMINATION` and `step3` does not execute. Otherwise, execution moves to `step3`. Additionally, if `step2` fails and the `Job` is restarted, then execution begins again on `step2`.

The following example shows the scenario in XML:

XML Configuration

    <step id="step1" parent="s1" next="step2">

    <step id="step2" parent="s2">
        <fail on="FAILED" exit-code="EARLY TERMINATION"/>
        <next on="*" to="step3"/>
    </step>

    <step id="step3" parent="s3">

The following example shows the scenario in Java:

Java Configuration

    @Bean
    public Job job() {
    	return this.jobBuilderFactory.get("job")
    			.start(step1())
    			.next(step2()).on("FAILED").fail()
    			.from(step2()).on("*").to(step3())
    			.end()
    			.build();
    }

##### Stopping a Job at a Given Step

Configuring a job to stop at a particular step instructs a `Job` to stop with a `BatchStatus` of `STOPPED`. Stopping a `Job` can provide a temporary break in processing, so that the operator can take some action before restarting the `Job`.

When using XML configuration, a 'stop' element requires a 'restart' attribute that specifies the step where execution should pick up when the Job is restarted.

When using Java configuration, the `stopAndRestart` method requires a 'restart' attribute that specifies the step where execution should pick up when the Job is restarted.

Consider the following scenario: if `step1` finishes with `COMPLETE`, then the job then stops. Once it is restarted, execution begins on `step2`.

The following listing shows the scenario in XML:

    <step id="step1" parent="s1">
        <stop on="COMPLETED" restart="step2"/>
    </step>

    <step id="step2" parent="s2"/>

The following example shows the scenario in Java:

    @Bean
    public Job job() {
    	return this.jobBuilderFactory.get("job")
    			.start(step1()).on("COMPLETED").stopAndRestart(step2())
    			.end()
    			.build();
    }

#### Programmatic Flow Decisions

In some situations, more information than the `ExitStatus` may be required to decide which step to execute next. In this case, a `JobExecutionDecider` can be used to assist in the decision, as shown in the following example:

    public class MyDecider implements JobExecutionDecider {
        public FlowExecutionStatus decide(JobExecution jobExecution, StepExecution stepExecution) {
            String status;
            if (someCondition()) {
                status = "FAILED";
            }
            else {
                status = "COMPLETED";
            }
            return new FlowExecutionStatus(status);
        }
    }

In the following sample job configuration, a `decision` specifies the decider to use as well as all of the transitions:

XML Configuration

    <job id="job">
        <step id="step1" parent="s1" next="decision" />

        <decision id="decision" decider="decider">
            <next on="FAILED" to="step2" />
            <next on="COMPLETED" to="step3" />
        </decision>

        <step id="step2" parent="s2" next="step3"/>
        <step id="step3" parent="s3" />
    </job>

    <beans:bean id="decider" class="com.MyDecider"/>

In the following example, a bean implementing the `JobExecutionDecider` is passed directly to the `next` call when using Java configuration.

Java Configuration

    @Bean
    public Job job() {
    	return this.jobBuilderFactory.get("job")
    			.start(step1())
    			.next(decider()).on("FAILED").to(step2())
    			.from(decider()).on("COMPLETED").to(step3())
    			.end()
    			.build();
    }

#### Split Flows

Every scenario described so far has involved a `Job` that executes its steps one at a time in a linear fashion. In addition to this typical style, Spring Batch also allows for a job to be configured with parallel flows.

The XML namespace allows you to use the 'split' element. As the following example shows, the 'split' element contains one or more 'flow' elements, where entire separate flows can be defined. A 'split' element may also contain any of the previously discussed transition elements, such as the 'next' attribute or the 'next', 'end' or 'fail' elements.

    <split id="split1" next="step4">
        <flow>
            <step id="step1" parent="s1" next="step2"/>
            <step id="step2" parent="s2"/>
        </flow>
        <flow>
            <step id="step3" parent="s3"/>
        </flow>
    </split>
    <step id="step4" parent="s4"/>

Java based configuration lets you configure splits through the provided builders. As the following example shows, the 'split' element contains one or more 'flow' elements, where entire separate flows can be defined. A 'split' element may also contain any of the previously discussed transition elements, such as the 'next' attribute or the 'next', 'end' or 'fail' elements.

    @Bean
    public Flow flow1() {
    	return new FlowBuilder<SimpleFlow>("flow1")
    			.start(step1())
    			.next(step2())
    			.build();
    }

    @Bean
    public Flow flow2() {
    	return new FlowBuilder<SimpleFlow>("flow2")
    			.start(step3())
    			.build();
    }

    @Bean
    public Job job(Flow flow1, Flow flow2) {
    	return this.jobBuilderFactory.get("job")
    				.start(flow1)
    				.split(new SimpleAsyncTaskExecutor())
    				.add(flow2)
    				.next(step4())
    				.end()
    				.build();
    }

#### Externalizing Flow Definitions and Dependencies Between Jobs

Part of the flow in a job can be externalized as a separate bean definition and then re-used. There are two ways to do so. The first is to simply declare the flow as a reference to one defined elsewhere.

The following example shows how to declare a flow as a reference to a flow defined elsewhere in XML:

XML Configuration

    <job id="job">
        <flow id="job1.flow1" parent="flow1" next="step3"/>
        <step id="step3" parent="s3"/>
    </job>

    <flow id="flow1">
        <step id="step1" parent="s1" next="step2"/>
        <step id="step2" parent="s2"/>
    </flow>

The following example shows how to declare a flow as a reference to a flow defined elsewhere in Java:

Java Confguration

    @Bean
    public Job job() {
    	return this.jobBuilderFactory.get("job")
    				.start(flow1())
    				.next(step3())
    				.end()
    				.build();
    }

    @Bean
    public Flow flow1() {
    	return new FlowBuilder<SimpleFlow>("flow1")
    			.start(step1())
    			.next(step2())
    			.build();
    }

The effect of defining an external flow as shown in the preceding example is to insert the steps from the external flow into the job as if they had been declared inline. In this way, many jobs can refer to the same template flow and compose such templates into different logical flows. This is also a good way to separate the integration testing of the individual flows.

The other form of an externalized flow is to use a `JobStep`. A `JobStep` is similar to a `FlowStep` but actually creates and launches a separate job execution for the steps in the flow specified.

The following example hows an example of a `JobStep` in XML:

XML Configuration

    <job id="jobStepJob" restartable="true">
       <step id="jobStepJob.step1">
          <job ref="job" job-launcher="jobLauncher"
              job-parameters-extractor="jobParametersExtractor"/>
       </step>
    </job>

    <job id="job" restartable="true">...</job>

    <bean id="jobParametersExtractor" class="org.spr...DefaultJobParametersExtractor">
       <property name="keys" value="input.file"/>
    </bean>

The following example shows an example of a `JobStep` in Java:

Java Configuration

    @Bean
    public Job jobStepJob() {
    	return this.jobBuilderFactory.get("jobStepJob")
    				.start(jobStepJobStep1(null))
    				.build();
    }

    @Bean
    public Step jobStepJobStep1(JobLauncher jobLauncher) {
    	return this.stepBuilderFactory.get("jobStepJobStep1")
    				.job(job())
    				.launcher(jobLauncher)
    				.parametersExtractor(jobParametersExtractor())
    				.build();
    }

    @Bean
    public Job job() {
    	return this.jobBuilderFactory.get("job")
    				.start(step1())
    				.build();
    }

    @Bean
    public DefaultJobParametersExtractor jobParametersExtractor() {
    	DefaultJobParametersExtractor extractor = new DefaultJobParametersExtractor();

    	extractor.setKeys(new String[]{"input.file"});

    	return extractor;
    }

The job parameters extractor is a strategy that determines how the `ExecutionContext` for the `Step` is converted into `JobParameters` for the `Job` that is run. The `JobStep` is useful when you want to have some more granular options for monitoring and reporting on jobs and steps. Using `JobStep` is also often a good answer to the question: "How do I create dependencies between jobs?" It is a good way to break up a large system into smaller modules and control the flow of jobs.

### Late Binding of `Job` and `Step` Attributes

Both the XML and flat file examples shown earlier use the Spring `Resource` abstraction to obtain a file. This works because `Resource` has a `getFile` method, which returns a `java.io.File`. Both XML and flat file resources can be configured using standard Spring constructs:

The following example shows late binding in XML:

XML Configuration

    <bean id="flatFileItemReader"
          class="org.springframework.batch.item.file.FlatFileItemReader">
        <property name="resource"
                  value="file://outputs/file.txt" />
    </bean>

The following example shows late binding in Java:

Java Configuration

    @Bean
    public FlatFileItemReader flatFileItemReader() {
    	FlatFileItemReader<Foo> reader = new FlatFileItemReaderBuilder<Foo>()
    			.name("flatFileItemReader")
    			.resource(new FileSystemResource("file://outputs/file.txt"))
    			...
    }

The preceding `Resource` loads the file from the specified file system location. Note that absolute locations have to start with a double slash (`//`). In most Spring applications, this solution is good enough, because the names of these resources are known at compile time. However, in batch scenarios, the file name may need to be determined at runtime as a parameter to the job. This can be solved using '-D' parameters to read a system property.

The following example shows how to read a file name from a property in XML:

XML Configuration

    <bean id="flatFileItemReader"
          class="org.springframework.batch.item.file.FlatFileItemReader">
        <property name="resource" value="${input.file.name}" />
    </bean>

The following shows how to read a file name from a property in Java:

Java Configuration

    @Bean
    public FlatFileItemReader flatFileItemReader(@Value("${input.file.name}") String name) {
    	return new FlatFileItemReaderBuilder<Foo>()
    			.name("flatFileItemReader")
    			.resource(new FileSystemResource(name))
    			...
    }

All that would be required for this solution to work would be a system argument (such as `-Dinput.file.name="file://outputs/file.txt"`).

| Although a `PropertyPlaceholderConfigurer` can be used here, it is not necessary if the system property is always set because the `ResourceEditor` in Spring already filters and does placeholder replacement on system properties.

Often, in a batch setting, it is preferable to parametrize the file name in the `JobParameters` of the job, instead of through system properties, and access them that way. To accomplish this, Spring Batch allows for the late binding of various `Job` and `Step` attributes.

The following example shows how to parameterize a file name in XML:

XML Configuration

    <bean id="flatFileItemReader" scope="step"
          class="org.springframework.batch.item.file.FlatFileItemReader">
        <property name="resource" value="#{jobParameters['input.file.name']}" />
    </bean>

The following example shows how to parameterize a file name in Java:

Java Configuration

    @StepScope
    @Bean
    public FlatFileItemReader flatFileItemReader(@Value("#{jobParameters['input.file.name']}") String name) {
    	return new FlatFileItemReaderBuilder<Foo>()
    			.name("flatFileItemReader")
    			.resource(new FileSystemResource(name))
    			...
    }

Both the `JobExecution` and `StepExecution` level `ExecutionContext` can be accessed in the same way.

The following example shows how to access the `ExecutionContext` in XML:

XML Configuration

    <bean id="flatFileItemReader" scope="step"
          class="org.springframework.batch.item.file.FlatFileItemReader">
        <property name="resource" value="#{jobExecutionContext['input.file.name']}" />
    </bean>

XML Configuration

    <bean id="flatFileItemReader" scope="step"
          class="org.springframework.batch.item.file.FlatFileItemReader">
        <property name="resource" value="#{stepExecutionContext['input.file.name']}" />
    </bean>

The following example shows how to access the `ExecutionContext` in Java:

Java Configuration

    @StepScope
    @Bean
    public FlatFileItemReader flatFileItemReader(@Value("#{jobExecutionContext['input.file.name']}") String name) {
    	return new FlatFileItemReaderBuilder<Foo>()
    			.name("flatFileItemReader")
    			.resource(new FileSystemResource(name))
    			...
    }

Java Configuration

    @StepScope
    @Bean
    public FlatFileItemReader flatFileItemReader(@Value("#{stepExecutionContext['input.file.name']}") String name) {
    	return new FlatFileItemReaderBuilder<Foo>()
    			.name("flatFileItemReader")
    			.resource(new FileSystemResource(name))
    			...
    }

| Any bean that uses late-binding must be declared with scope="step". See Step Scope for more information. It should be noted that a `Step` bean should not be step-scoped. If late-binding is needed in a step definition, the components of that step (ie tasklet, item reader/writer, etc) are the ones that should be scoped instead.

| If you are using Spring 3.0 (or above), the expressions in step-scoped beans are in the Spring Expression Language, a powerful general purpose language with many interesting features. To provide backward compatibility, if Spring Batch detects the presence of older versions of Spring, it uses a native expression language that is less powerful and that has slightly different parsing rules. The main difference is that the map keys in the example above do not need to be quoted with Spring 2.5, but the quotes are mandatory in Spring 3.0.

#### Step Scope

All of the late binding examples shown earlier have a scope of “step” declared on the bean definition.

The following example shows an example of binding to step scope in XML:

XML Configuration

    <bean id="flatFileItemReader" scope="step"
          class="org.springframework.batch.item.file.FlatFileItemReader">
        <property name="resource" value="#{jobParameters[input.file.name]}" />
    </bean>

The following example shows an example of binding to step scope in Java:

Java Configuration

    @StepScope
    @Bean
    public FlatFileItemReader flatFileItemReader(@Value("#{jobParameters[input.file.name]}") String name) {
    	return new FlatFileItemReaderBuilder<Foo>()
    			.name("flatFileItemReader")
    			.resource(new FileSystemResource(name))
    			...
    }

Using a scope of `Step` is required in order to use late binding, because the bean cannot actually be instantiated until the `Step` starts, to allow the attributes to be found. Because it is not part of the Spring container by default, the scope must be added explicitly, by using the `batch` namespace or by including a bean definition explicitly for the `StepScope`, or by using the `@EnableBatchProcessing` annotation. Use only one of those methods. The following example uses the `batch` namespace:

    <beans xmlns="http://www.springframework.org/schema/beans"
           xmlns:batch="http://www.springframework.org/schema/batch"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xsi:schemaLocation="...">
    <batch:job .../>
    ...
    </beans>

The following example includes the bean definition explicitly:

    <bean class="org.springframework.batch.core.scope.StepScope" />

#### Job Scope

`Job` scope, introduced in Spring Batch 3.0, is similar to `Step` scope in configuration but is a Scope for the `Job` context, so that there is only one instance of such a bean per running job. Additionally, support is provided for late binding of references accessible from the `JobContext` using `#{..}` placeholders. Using this feature, bean properties can be pulled from the job or job execution context and the job parameters.

The following example shows an example of binding to job scope in XML:

XML Configuration

    <bean id="..." class="..." scope="job">
        <property name="name" value="#{jobParameters[input]}" />
    </bean>

XML Configuration

    <bean id="..." class="..." scope="job">
        <property name="name" value="#{jobExecutionContext['input.name']}.txt" />
    </bean>

The following example shows an example of binding to job scope in Java:

Java Configuration

    @JobScope
    @Bean
    public FlatFileItemReader flatFileItemReader(@Value("#{jobParameters[input]}") String name) {
    	return new FlatFileItemReaderBuilder<Foo>()
    			.name("flatFileItemReader")
    			.resource(new FileSystemResource(name))
    			...
    }

Java Configuration

    @JobScope
    @Bean
    public FlatFileItemReader flatFileItemReader(@Value("#{jobExecutionContext['input.name']}") String name) {
    	return new FlatFileItemReaderBuilder<Foo>()
    			.name("flatFileItemReader")
    			.resource(new FileSystemResource(name))
    			...
    }

Because it is not part of the Spring container by default, the scope must be added explicitly, by using the `batch` namespace, by including a bean definition explicitly for the JobScope, or using the `@EnableBatchProcessing` annotation (but not all of them). The following example uses the `batch` namespace:

    <beans xmlns="http://www.springframework.org/schema/beans"
    		  xmlns:batch="http://www.springframework.org/schema/batch"
    		  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    		  xsi:schemaLocation="...">

    <batch:job .../>
    ...
    </beans>

The following example includes a bean that explicitly defines the `JobScope`:

    <bean class="org.springframework.batch.core.scope.JobScope" />

| There are some practical limitations of using job-scoped beans in multi-threaded or partitioned steps. Spring Batch does not control the threads spawned in these use cases, so it is not possible to set them up correctly to use such beans. Hence, it is not recommended to use job-scoped beans in multi-threaded or partitioned steps.