Creating Batch Artifacts (original) (raw)

After you define a job in terms of its batch artifacts using the Job Specification Language (JSL), you create these artifacts as Java classes that implement the interfaces in the javax.batch.api package and its subpackages.

This section lists the main batch artifact interfaces, demonstrates how to access context objects from the batch runtime, and provides some examples.

The following topics are addressed here:

• Batch Artifact Interfaces
• Dependency Injection in Batch Artifacts
• Using the Context Objects from the Batch Runtime

Batch Artifact Interfaces

The following tables list the interfaces that you implement to create batch artifacts. The interface implementations are referenced from the elements described in Using the Job Specification Language.

Table 58-3 lists the interfaces to implement batch artifacts for chunk steps, task steps, and decision elements.

Table 58-4 lists the interfaces to implement batch artifacts for partitioned steps.

Table 58-5 lists the interfaces to implement batch artifacts for job and step listeners.

Table 58-3 Main Batch Artifact Interfaces

Table 58-4 Partition Batch Artifact Interfaces

Table 58-5 Listener Batch Artifact Interfaces

Dependency Injection in Batch Artifacts

To ensure that Contexts and Dependency Injection (CDI) works in your batch artifacts, follow these steps.

1. Define your batch artifact implementations as CDI named beans using the Named annotation.
   For example, define an item reader implementation in a chunk step as follows:

@Named("MyItemReaderImpl")  
public class MyItemReaderImpl implements ItemReader {  
    /* ... Override the ItemReader interface methods ... */  
}  

1. Provide a public, empty, no-argument constructor for your batch artifacts.
   For example, provide the following constructor for the artifact above:

public MyItemReaderImpl() {}  

1. Specify the CDI name for the batch artifacts in the job definition file, instead of using the fully qualified name of the class.
   For example, define the step for the artifact above as follows:

<step id="stepA" next="stepB">  
  <chunk>  
    <reader ref="MyItemReaderImpl"></reader>  
    ...  
  </chunk>  
</step>  

This example uses the CDI name (MyItemReaderImpl) instead of the fully qualified name of the class (com.example.pkg.MyItemReaderImpl) to specify a batch artifact. 4. Ensure that your module is a CDI bean archive by annotating your batch artifacts with the javax.enterprise.context.Dependent annotation or by including an empty beans.xml deployment description with your application. For example, the following batch artifact is annotated with@Dependent:

@Dependent  
@Named("MyItemReaderImpl")  
public class MyItemReaderImpl implements ItemReader { ... }  

You may encounter the following errors if you do not follow this procedure.

• The batch runtime cannot locate some batch artifacts.
• The batch artifacts throw null pointer exceptions when accessing injected objects.

Using the Context Objects from the Batch Runtime

The batch runtime provides context objects that implement theJobContext and StepContext interfaces in thejavax.batch.runtime.context package. These objects are associated with the current job and step, respectively, and enable you to do the following:

• Get information from the current job or step, such as its name, instance ID, execution ID, batch status, and exit status
• Set the user-defined exit status
• Store user data
• Get property values from the job or step definition

You can inject context objects from the batch runtime inside batch artifact implementations like item readers, item processors, item writers, batchlets, listeners, and so on. The following example demonstrates how to access property values from the job definition file in an item reader implementation:

@Dependent
@Named("MyItemReaderImpl")
public class MyItemReaderImpl implements ItemReader {
    @Inject
    JobContext jobCtx;

    public MyItemReaderImpl() {}

    @Override
    public void open(Serializable checkpoint) throws Exception {
        String fileName = jobCtx.getProperties()
                                .getProperty("log_file_name");
        ...
    }
    ...
}

See Dependency Injection in Batch Artifacts for instructions on how to define your batch artifacts to use dependency injection.