ComposableRecordReader.java
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上传日期:2018-01-08
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- /**
- * 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.hadoop.mapred.join;
- import java.io.IOException;
- import org.apache.hadoop.io.Writable;
- import org.apache.hadoop.io.WritableComparable;
- import org.apache.hadoop.mapred.RecordReader;
- /**
- * Additional operations required of a RecordReader to participate in a join.
- */
- public interface ComposableRecordReader<K extends WritableComparable,
- V extends Writable>
- extends RecordReader<K,V>, Comparable<ComposableRecordReader<K,?>> {
- /**
- * Return the position in the collector this class occupies.
- */
- int id();
- /**
- * Return the key this RecordReader would supply on a call to next(K,V)
- */
- K key();
- /**
- * Clone the key at the head of this RecordReader into the object provided.
- */
- void key(K key) throws IOException;
- /**
- * Returns true if the stream is not empty, but provides no guarantee that
- * a call to next(K,V) will succeed.
- */
- boolean hasNext();
- /**
- * Skip key-value pairs with keys less than or equal to the key provided.
- */
- void skip(K key) throws IOException;
- /**
- * While key-value pairs from this RecordReader match the given key, register
- * them with the JoinCollector provided.
- */
- void accept(CompositeRecordReader.JoinCollector jc, K key) throws IOException;
- }