DataJoinMapperBase.java Source code

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Here is the source code for DataJoinMapperBase.java

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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.contrib.utils.join;

import java.io.IOException;
import java.util.Iterator;

import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapred.JobConf;
import org.apache.hadoop.mapred.OutputCollector;
import org.apache.hadoop.mapred.Reporter;

/**
 * This abstract class serves as the base class for the mapper class of a data
 * join job. This class expects its subclasses to implement methods for the
 * following functionalities:
 * 
 * 1. Compute the source tag of input values 2. Compute the map output value
 * object 3. Compute the map output key object
 * 
 * The source tag will be used by the reducer to determine from which source
 * (which table in SQL terminology) a value comes. Computing the map output
 * value object amounts to performing projecting/filtering work in a SQL
 * statement (through the select/where clauses). Computing the map output key
 * amounts to choosing the join key. This class provides the appropriate plugin
 * points for the user defined subclasses to implement the appropriate logic.
 * 
 */
public abstract class DataJoinMapperBase extends JobBase {

    protected String inputFile = null;

    protected JobConf job = null;

    protected Text inputTag = null;

    protected Reporter reporter = null;

    public void configure(JobConf job) {
        super.configure(job);
        this.job = job;
        this.inputFile = job.get("map.input.file");
        this.inputTag = generateInputTag(this.inputFile);
    }

    /**
     * Determine the source tag based on the input file name.
     * 
     * @param inputFile
     * @return the source tag computed from the given file name.
     */
    protected abstract Text generateInputTag(String inputFile);

    /**
     * Generate a tagged map output value. The user code can also perform
     * projection/filtering. If it decides to discard the input record when
     * certain conditions are met,it can simply return a null.
     * 
     * @param value
     * @return an object of TaggedMapOutput computed from the given value.
     */
    protected abstract TaggedMapOutput generateTaggedMapOutput(Object value);

    /**
     * Generate a map output key. The user code can compute the key
     * programmatically, not just selecting the values of some fields. In this
     * sense, it is more general than the joining capabilities of SQL.
     * 
     * @param aRecord
     * @return the group key for the given record
     */
    protected abstract Text generateGroupKey(TaggedMapOutput aRecord);

    public void map(Object key, Object value, OutputCollector output, Reporter reporter) throws IOException {
        if (this.reporter == null) {
            this.reporter = reporter;
        }
        addLongValue("totalCount", 1);
        TaggedMapOutput aRecord = generateTaggedMapOutput(value);
        if (aRecord == null) {
            addLongValue("discardedCount", 1);
            return;
        }
        Text groupKey = generateGroupKey(aRecord);
        if (groupKey == null) {
            addLongValue("nullGroupKeyCount", 1);
            return;
        }
        output.collect(groupKey, aRecord);
        addLongValue("collectedCount", 1);
    }

    public void close() throws IOException {
        if (this.reporter != null) {
            this.reporter.setStatus(super.getReport());
        }
    }

    public void reduce(Object arg0, Iterator arg1, OutputCollector arg2, Reporter arg3) throws IOException {
        // TODO Auto-generated method stub

    }
}