JoinRecordReader.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 java.util.PriorityQueue;
- import org.apache.hadoop.io.Writable;
- import org.apache.hadoop.io.WritableComparable;
- import org.apache.hadoop.io.WritableComparator;
- import org.apache.hadoop.io.WritableUtils;
- import org.apache.hadoop.mapred.JobConf;
- /**
- * Base class for Composite joins returning Tuples of arbitrary Writables.
- */
- public abstract class JoinRecordReader<K extends WritableComparable>
- extends CompositeRecordReader<K,Writable,TupleWritable>
- implements ComposableRecordReader<K,TupleWritable> {
- public JoinRecordReader(int id, JobConf conf, int capacity,
- Class<? extends WritableComparator> cmpcl) throws IOException {
- super(id, capacity, cmpcl);
- setConf(conf);
- }
- /**
- * Emit the next set of key, value pairs as defined by the child
- * RecordReaders and operation associated with this composite RR.
- */
- public boolean next(K key, TupleWritable value) throws IOException {
- if (jc.flush(value)) {
- WritableUtils.cloneInto(key, jc.key());
- return true;
- }
- jc.clear();
- K iterkey = createKey();
- final PriorityQueue<ComposableRecordReader<K,?>> q = getRecordReaderQueue();
- while (!q.isEmpty()) {
- fillJoinCollector(iterkey);
- jc.reset(iterkey);
- if (jc.flush(value)) {
- WritableUtils.cloneInto(key, jc.key());
- return true;
- }
- jc.clear();
- }
- return false;
- }
- /** {@inheritDoc} */
- public TupleWritable createValue() {
- return createInternalValue();
- }
- /**
- * Return an iterator wrapping the JoinCollector.
- */
- protected ResetableIterator<TupleWritable> getDelegate() {
- return new JoinDelegationIterator();
- }
- /**
- * Since the JoinCollector is effecting our operation, we need only
- * provide an iterator proxy wrapping its operation.
- */
- protected class JoinDelegationIterator
- implements ResetableIterator<TupleWritable> {
- public boolean hasNext() {
- return jc.hasNext();
- }
- public boolean next(TupleWritable val) throws IOException {
- return jc.flush(val);
- }
- public boolean replay(TupleWritable val) throws IOException {
- return jc.replay(val);
- }
- public void reset() {
- jc.reset(jc.key());
- }
- public void add(TupleWritable item) throws IOException {
- throw new UnsupportedOperationException();
- }
- public void close() throws IOException {
- jc.close();
- }
- public void clear() {
- jc.clear();
- }
- }
- }