org.apache.samza.system.descriptors

Interface StreamExpander<OM>

Type Parameters:

OM - type of the messages in the resultant MessageStream

All Superinterfaces:

java.io.Serializable

public interface StreamExpander<OM>
extends java.io.Serializable

Expands the provided InputDescriptor to a sub-DAG of one or more operators on the StreamApplicationDescriptor, and returns a new MessageStream with the combined results. Called when StreamApplicationDescriptor.getInputStream(org.apache.samza.system.descriptors.InputDescriptor<M, ?>) is being used to get a MessageStream using an InputDescriptor from an expanding system descriptor.

This is provided by default by expanding system descriptor implementations and can not be overridden or set on a per stream level.

Method Summary

Modifier and Type	Method and Description
MessageStream<OM>	apply(StreamApplicationDescriptor streamAppDesc, InputDescriptor inputDescriptor) Expands the provided InputDescriptor to a sub-DAG of one or more operators on the StreamApplicationDescriptor, and returns a new MessageStream with the combined results.

Method Detail

apply

MessageStream<OM> apply(StreamApplicationDescriptor streamAppDesc,
                        InputDescriptor inputDescriptor)

Expands the provided InputDescriptor to a sub-DAG of one or more operators on the StreamApplicationDescriptor, and returns a new MessageStream with the combined results. Called when the InputDescriptor is being used to get an MessageStream using StreamApplicationDescriptor.getInputStream(org.apache.samza.system.descriptors.InputDescriptor<M, ?>).

Notes for system implementers:

Take care to avoid infinite recursion in the implementation; e.g., by ensuring that it doesn't call StreamApplicationDescriptor.getInputStream(org.apache.samza.system.descriptors.InputDescriptor<M, ?>) with an InputDescriptor from an expanding system descriptor (like this one) again.

It's the StreamExpander's responsibility to propagate any properties, including serde, from the user-provided InputDescriptor to the expanded input descriptors.

Parameters:

streamAppDesc - the StreamApplicationDescriptor to register the expanded sub-DAG of operators on

inputDescriptor - the InputDescriptor to be expanded

Returns:

the MessageStream containing the combined results of the sub-DAG of operators