org.apache.samza.application

Interface TaskApplication

All Superinterfaces:

SamzaApplication<TaskApplicationDescriptor>

@InterfaceStability.Evolving
public interface TaskApplication
extends SamzaApplication<TaskApplicationDescriptor>

A TaskApplication describes the inputs, outputs, state, configuration and the processing logic for the application in Samza's Low Level API.

A typical TaskApplication implementation consists of the following stages:

1. Configuring the inputs, outputs and state (tables) using the appropriate SystemDescriptors, StreamDescriptors and TableDescriptors
2. Adding these descriptors to the provided TaskApplicationDescriptor.
3. Defining the processing logic by implementing a StreamTask or AsyncStreamTask that operates on each IncomingMessageEnvelope one at a time.
4. Setting a TaskFactory using TaskApplicationDescriptor.withTaskFactory(org.apache.samza.task.TaskFactory) that creates instances of the task above. The TaskFactory implementation must be Serializable.

The following example TaskApplication removes page views older than 1 hour from the input stream:

 public class PageViewFilter implements TaskApplication {
   public void describe(TaskApplicationDescriptor appDescriptor) {
     KafkaSystemDescriptor trackingSystemDescriptor = new KafkaSystemDescriptor("tracking");
     KafkaInputDescriptor<PageViewEvent> inputStreamDescriptor =
         trackingSystemDescriptor.getInputDescriptor("pageViewEvent", new JsonSerdeV2<>(PageViewEvent.class));
     KafkaOutputDescriptor<PageViewEvent>> outputStreamDescriptor =
         trackingSystemDescriptor.getOutputDescriptor("recentPageViewEvent", new JsonSerdeV2<>(PageViewEvent.class)));

     appDescriptor
         .withInputStream(inputStreamDescriptor)
         .withOutputStream(outputStreamDescriptor)
         .withTaskFactory((StreamTaskFactory) () -> new PageViewTask());
   }
 }

 public class PageViewTask implements StreamTask {
   public void process(IncomingMessageEnvelope message, MessageCollector collector, TaskCoordinator coordinator) {
     PageViewEvent m = (PageViewEvent) message.getValue();
     if (m.getCreationTime() > System.currentTimeMillis() - Duration.ofHours(1).toMillis()) {
       collector.send(new OutgoingMessageEnvelope(
          new SystemStream("tracking", "recentPageViewEvent"), message.getKey(), message.getKey(), m));
     }
   }
 }
 

Method Summary

Methods inherited from interface org.apache.samza.application.SamzaApplication

describe