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CoGroupFunction.java
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CoGroupFunction.java
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/***********************************************************************************************************************
*
* Copyright (C) 2010 by the Stratosphere project (https://stratosphere.eu)
*
* Licensed 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
*
* https://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 eu.stratosphere.arraymodel.functions;
import java.lang.reflect.Method;
import java.util.Iterator;
import eu.stratosphere.api.functions.GenericCoGrouper;
import eu.stratosphere.types.Value;
import eu.stratosphere.util.Collector;
/**
* The CoGroupFunction must be extended to provide a co-grouper implementation which is called by a CoGroup PACT.
* By definition, a CoGroup PACT has two input sets of records. It calls the co-grouper implementation once for each
* distinct key in its inputs. Together with the key, two iterators over the records containing that key from both
* inputs are handed to the <code>coGroup()</code> method.
* For details on the CoGroup PACT read the documentation of the PACT programming model.
* <p>
* The CoGroupFunction extension must be parameterized with the type of the key of its input.
* <p>
* For a coGroup implementation, the <code>coGroup()</code> method must be implemented.
*/
public abstract class CoGroupFunction extends AbstractArrayModelFunction implements GenericCoGrouper<Value[], Value[], Value[]> {
/**
* This method must be implemented to provide a user implementation of a
* matcher. It is called for each two key-value pairs that share the same
* key and come from different inputs.
*
* @param records1 The records from the first input which were paired with the key.
* @param records2 The records from the second input which were paired with the key.
* @param out A collector that collects all output pairs.
*
* @throws Exception Implementations may forward exceptions, which are caught by the runtime. When the
* runtime catches an exception, it aborts the task and lets the fail-over logic
* decide whether to retry the task execution.
*/
@Override
public abstract void coGroup(Iterator<Value[]> records1, Iterator<Value[]> records2, Collector<Value[]> out);
@Override
public Method getUDFMethod() {
try {
return getClass().getMethod("coGroup", Iterator.class, Iterator.class, Collector.class);
} catch (Exception e) {
throw new RuntimeException(e);
}
}
}