15. Guidance and Examples

Spring for Apache Hadoop provides integration with the Spring Framework to create and run Hadoop MapReduce, Hive, and Pig jobs as well as work with HDFS and HBase. If you have simple needs to work with Hadoop, including basic scheduling, you can add the Spring for Apache Hadoop namespace to your Spring based project and get going quickly using Hadoop.

As the complexity of your Hadoop application increases, you may want to use Spring Batch to regain on the complexity of developing a large Hadoop application. Spring Batch provides an extension to the Spring programming model to support common batch job scenarios characterized by the processing of large amounts of data from flat files, databases and messaging systems. It also provides a workflow style processing model, persistent tracking of steps within the workflow, event notification, as well as administrative functionality to start/stop/restart a workflow. As Spring Batch was designed to be extended, Spring for Apache Hadoop plugs into those extensibilty points, allowing for Hadoop related processing to be a first class citizen in the Spring Batch processing model.

Another project of interest to Hadoop developers is Spring Integration. Spring Integration provides an extension of the Spring programming model to support the well-known Enterprise Integration Patterns. It enables lightweight messaging within Spring-based applications and supports integration with external systems via declarative adapters. These adapters are of particular interest to Hadoop developers, as they directly support common Hadoop use-cases such as polling a directory or FTP folder for the presence of a file or group of files. Then once the files are present, a message is sent internally to the application to do additional processing. This additional processing can be calling a Hadoop MapReduce job directly or starting a more complex Spring Batch based workflow. Similarly, a step in a Spring Batch workflow can invoke functionality in Spring Integration, for example to send a message though an email adapter.

No matter if you use the Spring Batch project with the Spring Framework by itself or with additional extentions such as Spring Batch and Spring Integration that focus on a particular domain, you will benefit from the core values that Spring projects bring to the table, namely enabling modularity, reuse and extensive support for unit and integration testing.

15.1 Scheduling

Spring Batch integrates with a variety of job schedulers and is not a scheduling framework. There are many good enterprise schedulers available in both the commercial and open source spaces such as Quartz, Tivoli, Control-M, etc. It is intended to work in conjunction with a scheduler, not replace a scheduler. As a lightweight solution, you can use Spring’s built in scheduling support that will give you cron-like and other basic scheduling trigger functionality. See the Task Execution and Scheduling documention for more info. A middle ground it to use Spring’s Quartz integration, see Using the OpenSymphony Quartz Scheduler for more information. The Spring Batch distribution contains an example, but this documentation will be updated to provide some more directed examples with Hadoop, check for updates on the main web site of Spring for Apache Hadoop.

15.2 Batch Job Listeners

Spring Batch lets you attach listeners at the job and step levels to perform additional processing. For example, at the end of a job you can perform some notification or perhaps even start another Spring Batch job. As a brief example, implement the interface JobExecutionListener and configure it into the Spring Batch job as shown below.

<batch:job id="job1">
  <batch:step id="import" next="wordcount">
    <batch:tasklet ref="script-tasklet"/>

  <batch:step id="wordcount">
    <batch:tasklet ref="wordcount-tasklet" />

   <batch:listener ref="simpleNotificatonListener"/>


<bean id="simpleNotificatonListener" class="com.mycompany.myapp.SimpleNotificationListener"/>