This version is still in development and is not considered stable yet. For the latest stable version, please use Spring Batch Documentation 5.1.2!spring-doc.cn

This version is still in development and is not considered stable yet. For the latest stable version, please use Spring Batch Documentation 5.1.2!spring-doc.cn

Chunk-oriented processing is not the only way to process in a Step. What if a Step must consist of a 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.spring-doc.cn

The Tasklet interface 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 SQL update statement.spring-doc.cn

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:spring-doc.cn

@Bean
public Step step1(JobRepository jobRepository, PlatformTransactionManager transactionManager) {
    return new StepBuilder("step1", jobRepository)
    			.tasklet(myTasklet(), transactionManager)
    			.build();
}

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:spring-doc.cn

<step id="step1">
    <tasklet ref="myTasklet"/>
</step>
If it implements the StepListener interface, TaskletStep automatically registers the tasklet as a StepListener.
If it implements the StepListener interface, TaskletStep automatically registers the tasklet as a StepListener.

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. You can use the TaskletAdapter to call this class without having to write an adapter for the Tasklet interface.spring-doc.cn

The following example shows how to define a TaskletAdapter in Java:spring-doc.cn

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

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

	return adapter;
}

The following example shows how to define a TaskletAdapter in XML:spring-doc.cn

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>

Example Tasklet Implementation

Many batch jobs contain steps that must be done before the main processing begins, 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:spring-doc.cn

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(), "The resource must be a directory");

        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.state(directory != null, "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.spring-doc.cn

The following example shows how to reference the tasklet from the step in Java:spring-doc.cn

Java Configuration
@Bean
public Job taskletJob(JobRepository jobRepository, Step deleteFilesInDir) {
	return new JobBuilder("taskletJob", jobRepository)
				.start(deleteFilesInDir)
				.build();
}

@Bean
public Step deleteFilesInDir(JobRepository jobRepository, PlatformTransactionManager transactionManager) {
	return new StepBuilder("deleteFilesInDir", jobRepository)
				.tasklet(fileDeletingTasklet(), transactionManager)
				.build();
}

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

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

	return tasklet;
}

The following example shows how to reference the tasklet from the step in XML:spring-doc.cn

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

<beans:bean id="fileDeletingTasklet"
            class="org.springframework.batch.samples.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>