Adding Functionality to Apache NiFi
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Developing a Reporting Task

Just like with the Processor and ControllerService interfaces, the ReportingTask interface exposes methods for configuration, validation, and initialization. These methods are all identical to those of the Processor and ControllerService interfaces except that the initialize method is passed a ReportingConfiguration object, as opposed to the initialization objects received by the other Components. The ReportingTask also has an onTrigger method that is invoked by the framework to trigger the task to perform its job.

Within the onTrigger method, the ReportingTask is given access to a ReportingContext, from which configuration and information about the NiFi instance can be obtained. The BulletinRepository allows Bulletins to be queried and allows the ReportingTask to submit its own Bulletins, so that information will be rendered to users. The ControllerServiceLookup that is accessible via the Context provides access to ControllerServices that have been configured. However, this method of obtaining Controller Services is not the preferred method. Rather, the preferred method for obtaining a Controller Service is to reference the Controller Service in a PropertyDescriptor, as is discussed in the Interacting with a Controller Service section.

The EventAccess object that is exposed via the ReportingContext provides access to the ProcessGroupStatus, which exposes statistics about the amount of data processed in the past five minutes by Process Groups, Processors, Connections, and other Components. Additionally, the EventAccess object provides access to the ProvenanceEventRecords that have been stored in the ProvenanceEventRepository. These Provenance Events are emitted by Processors when data is received from external sources, emitted to external services, removed from the system, modified, or routed according to some decision that was made.

Each ProvenanceEvent has the ID of the FlowFile, the type of Event, the creation time of the Event, and all FlowFile attributes associated with the FlowFile at the time that the FlowFile was accessed by the component as well as the FlowFile attributes that were associated with the FlowFile as a result of the processing that the event describes. This provides a great deal of information to ReportingTasks, allowing reports to be generated in many different ways to expose metrics and monitoring capabilities needed for any number of operational concerns.