org.apache.samza.task

Interface StreamTask

public interface StreamTask

A StreamTask is the basic class on which Samza jobs are implemented. Developers writing Samza jobs begin by implementing this class, which processes messages from the job's input streams and writes messages out to streams via the provided MessageCollector. A StreamTask may be augmented by implementing other interfaces, such as InitableTask, WindowableTask, or ClosableTask.

The methods of StreamTasks and associated other tasks are guaranteed to be called in a single-threaded fashion; no extra synchronization is necessary on the part of the class implementer. References to instances of IncomingMessageEnvelopes,MessageCollectors, and TaskCoordinator should not be held onto between calls; there is no guarantee that these will not be invalidated or otherwise used by the framework.

Method Summary

Modifier and Type	Method and Description
void	process(IncomingMessageEnvelope envelope, MessageCollector collector, TaskCoordinator coordinator) Called once for each message that this StreamTask receives.

Method Detail

process

void process(IncomingMessageEnvelope envelope,
             MessageCollector collector,
             TaskCoordinator coordinator)
      throws java.lang.Exception

Called once for each message that this StreamTask receives.

Parameters:

envelope - Contains the received deserialized message and key, and also information regarding the stream and partition of which the message was received from.

collector - Contains the means of sending message envelopes to the output stream. The collector must only be used during the current call to the process method; you should not reuse the collector between invocations of this method.

coordinator - Manages execution of tasks.

Throws:

java.lang.Exception - Any exception types encountered during the execution of the processing task.