| /* |
| * Licensed to the Apache Software Foundation (ASF) under one |
| * or more contributor license agreements. See the NOTICE file |
| * distributed with this work for additional information |
| * regarding copyright ownership. The ASF licenses this file |
| * to you under the Apache License, Version 2.0 (the |
| * "License"); you may not use this file except in compliance |
| * with the License. You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, |
| * software distributed under the License is distributed on an |
| * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY |
| * KIND, either express or implied. See the License for the |
| * specific language governing permissions and limitations |
| * under the License. |
| */ |
| package org.apache.samza.system.descriptors; |
| |
| import java.io.Serializable; |
| import org.apache.samza.application.descriptors.StreamApplicationDescriptor; |
| import org.apache.samza.operators.MessageStream; |
| |
| /** |
| * Expands the provided {@link InputDescriptor} to a sub-DAG of one or more operators on the |
| * {@link StreamApplicationDescriptor}, and returns a new {@link MessageStream} with the combined results. |
| * Called when {@link StreamApplicationDescriptor#getInputStream} is being used to get a {@link MessageStream} using an |
| * {@link InputDescriptor} from an expanding system descriptor. |
| * <p> |
| * This is provided by default by expanding system descriptor implementations and can not be overridden |
| * or set on a per stream level. |
| * |
| * @param <OM> type of the messages in the resultant {@link MessageStream} |
| */ |
| public interface StreamExpander<OM> extends Serializable { |
| |
| /** |
| * Expands the provided {@link InputDescriptor} to a sub-DAG of one or more operators on the {@link StreamApplicationDescriptor}, |
| * and returns a new {@link MessageStream} with the combined results. Called when the {@link InputDescriptor} |
| * is being used to get an {@link MessageStream} using {@link StreamApplicationDescriptor#getInputStream}. |
| * <p> |
| * Notes for system implementers: |
| * <p> |
| * Take care to avoid infinite recursion in the implementation; e.g., by ensuring that it doesn't call |
| * {@link StreamApplicationDescriptor#getInputStream} with an {@link InputDescriptor} from an expanding system descriptor |
| * (like this one) again. |
| * <p> |
| * It's the {@link StreamExpander}'s responsibility to propagate any properties, including serde, from the |
| * user-provided {@link InputDescriptor} to the expanded input descriptors. |
| * |
| * @param streamAppDesc the {@link StreamApplicationDescriptor} to register the expanded sub-DAG of operators on |
| * @param inputDescriptor the {@link InputDescriptor} to be expanded |
| * @return the {@link MessageStream} containing the combined results of the sub-DAG of operators |
| */ |
| MessageStream<OM> apply(StreamApplicationDescriptor streamAppDesc, InputDescriptor inputDescriptor); |
| |
| } |