Confusion about executionContexts in Spring Batch

Question

What exactly is an executionContext in Spring batch? What does getting a handle on it allow us to do? It seems like an overloaded use of the term executionContext. What is the difference between the two "Contexts" below? One of them has jobParameters and the other just gets the execution context. But the first one gets jobParameters from the StepExecution rather than the job. It's confusing me. How many different kinds of execution contexts are there?

chunkContext.getStepContext()
                        .getStepExecution().getJobParameters()

chunkContext.getStepContext()
                .getStepExecution().getJobExecution().getExecutionContext()

Any enlightenment you can provide would be a great help.

Thanks in advance.

Answer 1

Within Spring Batch there are two ExecutionContexts. The first is at the Job level. The second is at the Step level. In each case, the ExecutionContext serves as a storage area for information pertinent to that level. For example, in the Step's ExecutionContext, the state of a step (how many records have been read, etc) is typically stored so that on restart the reader and writer can be reset to the correct position. The Job's ExecutionContext is typically used to share information across steps.

With that being said, in the case of what you posted above is the getting of JobParameters from the StepExecution. This is really just a shortcut to getting them from the JobExecution. What you're doing in the first line is the same as:

chunkContext.getStepContext()
            .getStepExecution()
            .getJobExecution()
            .getJobParameters();

The JobParameters have no bearing on the ExecutionContext. They are the parameters passed into a job much like the String [] args passed to a public static void main(String[] args).

Where the confusion may lie is the StepContext. The StepContext serves as a wrapper for the StepExecution that allows the StepScope's accessors to work. For example, when you configure a job with a bean like this:

    <beans:bean id="outputFile"
    class="org.springframework.core.io.FileSystemResource" scope="step">
    <beans:constructor-arg value="#{jobParameters[outputFile]}" />
</beans:bean>

The #{jobParameters[outputFile]} is being roughly evaluated to StepContext.getJobParameters().getString("outputFile");.