55.2.1 The Batch Processing Framework

Java EE includes a batch processing framework that consists of the following elements:

• A batch runtime that manages the execution of jobs

• A job specification language based on XML

• A Java API to interact with the batch runtime

• A Java API to implement steps, decision elements, and other batch artifacts

Batch applications in Java EE contain XML files and Java classes. The XML files define the structure of a job in terms of batch artifacts and the relationships between them. (A batch artifact is a part of a chunk-oriented step, a task-oriented step, a decision element, or another component of a batch application). The Java classes implement the application logic of the batch artifacts defined in the XML files. The batch runtime parses the XML files and loads the batch artifacts as Java classes to run the jobs in a batch application.

55.2.2 Creating Batch Applications

The process for creating a batch application in Java EE is the following.

1. Design the batch application.

   1. Identify the input sources, the format of the input data, the desired final result, and the required processing phases.

   2. Organize the application as a job with chunk-oriented steps, task-oriented steps, and decision elements. Determine the dependencies between them.

   3. Determine the order of execution in terms of transitions between steps.

   4. Identify steps that can run in parallel and steps that can run in more than one thread.

2. Create the batch artifacts as Java classes by implementing the interfaces specified by the framework for steps, decision elements, and so on. These Java classes contain the code to read data from input sources, format items, process items, and store results. Batch artifacts can access context objects from the batch runtime using dependency injection.

3. Define jobs, steps, and their execution flow in XML files using the Job Specification Language. The elements in the XML files reference batch artifacts implemented as Java classes. The batch artifacts can access properties declared in the XML files, such as names of files and databases.

4. Use the Java API provided by the batch runtime to launch the batch application.

The following sections describe in detail how to use the components of the batch processing framework in Java EE to create batch applications.

55.2.3 Elements of a Batch Job

A batch job can contain one or more of the following elements:

• Steps

• Flows

• Splits

• Decision elements

Steps are described in Introduction to Batch Processing, and can be chunk-oriented or task-oriented. Chunk-oriented steps can be partitioned steps. In a partitioned chunk step, the processing of one item does not depend on other items, so these steps can run in more than one thread.

A flow is a sequence of steps that execute as a unit. A sequence of related steps can be grouped together into a flow. The steps in a flow cannot transition to steps outside the flow. The flow transitions to the next element when its last step completes.

A split is a set of flows that execute in parallel; each flow runs on a separate thread. The split transitions to the next element when all its flows complete.

Decision elements use the exit status of the previous step to determine the next step or to terminate the batch job.

55.2.4 Properties and Parameters

Jobs and steps can have a number of properties associated with them. You define properties in the job definition file, and batch artifacts access these properties using context objects from the batch runtime. Using properties in this manner enables you to decouple static parameters of the job from the business logic and to reuse batch artifacts in different job definition files.

Specifying properties is described in Using the Job Specification Language, and accessing properties in batch artifacts is described in Creating Batch Artifacts.

Java EE applications can also pass parameters to a job when they submit it to the batch runtime. This enables you to specify dynamic parameters that are only known at runtime. Parameters are also necessary for partitioned steps, since each partition needs to know, for example, what range of items to process.

Specifying parameters when submitting jobs is described in Submitting Jobs to the Batch Runtime. Specifying parameters for partitioned steps and accessing them in batch artifacts is demonstrated in The phonebilling Example Application.

55.2.5 Job Instances and Job Executions

A job definition can have multiple instances, each with different parameters. A job execution is an attempt to run a job instance. The batch runtime maintains information about job instances and job executions, as described in Checking the Status of a Job.

55.2.6 Batch and Exit Status

The state of jobs, steps, splits, and flows is represented in the batch runtime as a batch status value. Batch status values are listed Table 55-1. They are represented as strings.

Java EE applications can submit jobs and access the batch status of a job using the JobOperator interface, as described in Submitting Jobs to the Batch Runtime. Job definition files can refer to batch status values using the Job Specification Language (JSL), as described in Using the Job Specification Language. Batch artifacts can access batch status values using context objects, as described in Using the Context Objects from the Batch Runtime.

For flows, the batch status is that of its last step. For splits, the batch status is the following:

• COMPLETED: If all its flows have a batch status of COMPLETED

• FAILED: If any flow has a batch status of FAILED

• STOPPED: If any flow has a batch status of STOPPED, and no flows have a batch status of FAILED

The batch status for jobs, steps, splits, and flows is set by the batch runtime. Jobs, steps, splits, and flows also have an exit status, which is a user-defined value based on the batch status. You can set the exit status inside batch artifacts or in the job definition file. You can access the exit status in the same manner as the batch status, described above. The default value for the exit status is the same as the batch status.