Spring for Apache Hadoop provides for each Hadoop interaction type, whether it is vanilla Map/Reduce, Cascading, Hive or Pig, a runner, a dedicated class used for declarative (or programmatic) interaction. The list below illustrates the existing runner classes for each type, its name and namespace element
Table 8.1. Available Runners
| Type | Name | Namespace element | Description |
|---|---|---|---|
Map/Reduce Job | JobRunner | job-runner | Runner for Map/Reduce jobs, whether vanilla M/R or streaming |
Hadoop Tool | ToolRunner | tool-runner | Runner for Hadoop Tools (whether stand-alone or as jars). |
Hadoop jars | JarRunner | jar-runner | Runner for Hadoop jars. |
| Hive queries and scripts | HiveRunner | hive-runner | Runner for executing Hive queries or scripts. |
| Pig queries and scripts | PigRunner | pig-runner | Runner for executing Pig scripts. |
Cascading Cascades | CascadeRunner | - | Runner for executing Cascading Cascades. |
| JSR-223/JVM scripts | HdfsScriptRunner | script | Runner for executing JVM 'scripting' languages (implementing the JSR-223 API). |
While most of the configuration depends on the underlying type, the runners share common attributes and behaviour so one can use them in a predictive, consistent way. Below is a list of common features:
declaration does not imply execution
The runner allows a script, a job, a cascade to run but the execution can be triggered either programmatically or by the container at start-up.
run-at-startup
Each runner can execute its action at start-up. By default, this flag is set to false. For multiple or on demand execution (such as scheduling) use the Callable contract (see below).
JDK Callable interface
Each runner implements the JDK Callable interface. Thus one can inject the runner into other beans or its own classes to trigger the execution
(as many or as little times as she wants).
pre and post actions
Each runner allows one or multiple, pre or/and post actions to be specified (to chain them together such as executing a job after another or perfoming clean up). Typically other runners can be used but any Callable can be specified. The actions will be executed
before and after the main action, in the declaration order. The runner uses a fail-safe behaviour meaning, any exception will interrupt the run and will propagated immediately to the caller.
consider Spring Batch
The runners are meant as a way to execute basic tasks. When multiple executions need to be coordinated and the flow becomes non-trivial, we strongly recommend using Spring Batch which provides all the features of the runners and more (a complete, mature framework for batch execution).