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 that returns a java.io.File. You can configure both XML and flat file resources by using standard Spring constructs:spring-doc.cn

The following example shows late binding in Java:spring-doc.cn

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

The following example shows late binding in XML:spring-doc.cn

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

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.spring-doc.cn

The following shows how to read a file name from a property in Java:spring-doc.cn

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

The following example shows how to read a file name from a property in XML:spring-doc.cn

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

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

Although you can use a PropertyPlaceholderConfigurer 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 parameterize 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.spring-doc.cn

The following example shows how to parameterize a file name in Java:spring-doc.cn

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

The following example shows how to parameterize a file name in XML:spring-doc.cn

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

You can access both the JobExecution and StepExecution level ExecutionContext in the same way.spring-doc.cn

The following example shows how to access the ExecutionContext in Java:spring-doc.cn

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))
			...
}

The following example shows how to access the ExecutionContext in XML:spring-doc.cn

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>
Any bean that uses late binding must be declared with scope="step". See Step Scope for more information. A Step bean should not be step-scoped. If late binding is needed in a step definition, the components of that step (tasklet, item reader or writer, and so on) are the ones that should be scoped instead.
If you use 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.spring-doc.cn

The following example shows an example of binding to step scope in Java:spring-doc.cn

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

The following example shows an example of binding to step scope in XML:spring-doc.cn

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

Using a scope of Step is required to use late binding, because the bean cannot actually be instantiated until the Step starts, to let the attributes be found. 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 StepScope, or by using the @EnableBatchProcessing annotation. Use only one of those methods. The following example uses the batch namespace:spring-doc.cn

<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:spring-doc.cn

<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 by using #{..} placeholders. Using this feature, you can pull bean properties from the job or job execution context and the job parameters.spring-doc.cn

The following example shows an example of binding to job scope in Java:spring-doc.cn

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))
			...
}

The following example shows an example of binding to job scope in XML:spring-doc.cn

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>

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 by using the @EnableBatchProcessing annotation (choose only one approach). The following example uses the batch namespace:spring-doc.cn

<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:spring-doc.cn

<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, we do not recommend using job-scoped beans in multi-threaded or partitioned steps.

Scoping ItemStream components

When using the Java configuration style to define job or step scoped ItemStream beans, the return type of the bean definition method should be at least ItemStream. This is required so that Spring Batch correctly creates a proxy that implements this interface, and therefore honors its contract by calling open, update and close methods as expected.spring-doc.cn

It is recommended to make the bean definition method of such beans return the most specific known implementation, as shown in the following example:spring-doc.cn

Define a step-scoped bean with the most specific return type
@Bean
@StepScope
public FlatFileItemReader flatFileItemReader(@Value("#{jobParameters['input.file.name']}") String name) {
	return new FlatFileItemReaderBuilder<Foo>()
			.resource(new FileSystemResource(name))
			// set other properties of the item reader
			.build();
}