pregelix/pregelix-api/src/main/java/edu/uci/ics/pregelix/api/io/VertexOutputFormat.java

/*
 * Copyright 2009-2013 by The Regents of the University of California
 * 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 from
 * 
 *     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 edu.uci.ics.pregelix.api.io;

import java.io.IOException;

import org.apache.hadoop.io.Writable;
import org.apache.hadoop.io.WritableComparable;
import org.apache.hadoop.mapreduce.InputSplit;
import org.apache.hadoop.mapreduce.JobContext;
import org.apache.hadoop.mapreduce.OutputCommitter;
import org.apache.hadoop.mapreduce.TaskAttemptContext;

/**
 * Implement to output the graph after the computation. It is modeled directly
 * after the Hadoop OutputFormat.
 * 
 * @param <I>
 *            Vertex index value
 * @param <V>
 *            Vertex value
 * @param <E>
 *            Edge value
 */
@SuppressWarnings("rawtypes")
public abstract class VertexOutputFormat<I extends WritableComparable, V extends Writable, E extends Writable> {
    /**
     * Create a vertex writer for a given split. The framework will call {@link VertexReader#initialize(InputSplit, TaskAttemptContext)} before
     * the split is used.
     * 
     * @param context
     *            the information about the task
     * @return a new vertex writer
     * @throws IOException
     * @throws InterruptedException
     */
    public abstract VertexWriter<I, V, E> createVertexWriter(TaskAttemptContext context) throws IOException,
            InterruptedException;

    /**
     * Check for validity of the output-specification for the job. (Copied from
     * Hadoop OutputFormat)
     * <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. (Copied from Hadoop
     * OutputFormat)
     * 
     * @param context
     *            the task context
     * @return an output committer
     * @throws IOException
     * @throws InterruptedException
     */
    public abstract OutputCommitter getOutputCommitter(TaskAttemptContext context) throws IOException,
            InterruptedException;
}