OutputFormat.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.mapreduce;
- import java.io.IOException;
- import org.apache.hadoop.fs.FileSystem;
- /**
- * <code>OutputFormat</code> describes the output-specification for a
- * Map-Reduce job.
- *
- * <p>The Map-Reduce framework relies on the <code>OutputFormat</code> of the
- * job to:<p>
- * <ol>
- * <li>
- * Validate the output-specification of the job. For e.g. check that the
- * output directory doesn't already exist.
- * <li>
- * Provide the {@link RecordWriter} implementation to be used to write out
- * the output files of the job. Output files are stored in a
- * {@link FileSystem}.
- * </li>
- * </ol>
- *
- * @see RecordWriter
- */
- public abstract class OutputFormat<K, V> {
- /**
- * Get the {@link RecordWriter} for the given task.
- *
- * @param context the information about the current task.
- * @return a {@link RecordWriter} to write the output for the job.
- * @throws IOException
- */
- public abstract RecordWriter<K, V>
- getRecordWriter(TaskAttemptContext context
- ) throws IOException, InterruptedException;
- /**
- * Check for validity of the output-specification for the job.
- *
- * <p>This is to validate the output specification for the job when it is
- * a job is submitted. Typically checks that it does not already exist,
- * throwing an exception when it already exists, so that output is not
- * overwritten.</p>
- *
- * @param context information about the job
- * @throws IOException when output should not be attempted
- */
- public abstract void checkOutputSpecs(JobContext context
- ) throws IOException,
- InterruptedException;
- /**
- * Get the output committer for this output format. This is responsible
- * for ensuring the output is committed correctly.
- * @param context the task context
- * @return an output committer
- * @throws IOException
- * @throws InterruptedException
- */
- public abstract
- OutputCommitter getOutputCommitter(TaskAttemptContext context
- ) throws IOException, InterruptedException;
- }