RecordReader.java
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上传日期:2018-01-08
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文件大小:3k
- /**
- * 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;
- import java.io.IOException;
- import java.io.DataInput;
- /**
- * <code>RecordReader</code> reads <key, value> pairs from an
- * {@link InputSplit}.
- *
- * <p><code>RecordReader</code>, typically, converts the byte-oriented view of
- * the input, provided by the <code>InputSplit</code>, and presents a
- * record-oriented view for the {@link Mapper} & {@link Reducer} tasks for
- * processing. It thus assumes the responsibility of processing record
- * boundaries and presenting the tasks with keys and values.</p>
- *
- * @see InputSplit
- * @see InputFormat
- */
- public interface RecordReader<K, V> {
- /**
- * Reads the next key/value pair from the input for processing.
- *
- * @param key the key to read data into
- * @param value the value to read data into
- * @return true iff a key/value was read, false if at EOF
- */
- boolean next(K key, V value) throws IOException;
-
- /**
- * Create an object of the appropriate type to be used as a key.
- *
- * @return a new key object.
- */
- K createKey();
-
- /**
- * Create an object of the appropriate type to be used as a value.
- *
- * @return a new value object.
- */
- V createValue();
- /**
- * Returns the current position in the input.
- *
- * @return the current position in the input.
- * @throws IOException
- */
- long getPos() throws IOException;
- /**
- * Close this {@link InputSplit} to future operations.
- *
- * @throws IOException
- */
- public void close() throws IOException;
- /**
- * How much of the input has the {@link RecordReader} consumed i.e.
- * has been processed by?
- *
- * @return progress from <code>0.0</code> to <code>1.0</code>.
- * @throws IOException
- */
- float getProgress() throws IOException;
- }