edu.yale.cs.hadoopdb.sms.connector.SMSRecordReader.java Source code

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/**
 * Copyright 2009 HadoopDB Team (http://db.cs.yale.edu/hadoopdb/hadoopdb.html)
 *
 * 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 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 edu.yale.cs.hadoopdb.sms.connector;

import java.io.IOException;
import java.sql.SQLException;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapred.JobConf;
import org.apache.hadoop.mapred.RecordReader;

import edu.yale.cs.hadoopdb.connector.AbstractDBRecordReader;
import edu.yale.cs.hadoopdb.sms.connector.SMSInputFormat;
import edu.yale.cs.hadoopdb.sms.connector.SMSInputSplit;
import edu.yale.cs.hadoopdb.sms.connector.SMSRecordReader;
import edu.yale.cs.hadoopdb.util.ParseSchema;

/**
 * SMSRecordReaders extends AbstractDBRecordReader and specializes the
 * value class to Text (in contrast to DBRecordReader that allows
 * arbitrary value classes). Hive expects the value to be set of field values
 * delimited by a special character {@link ParseSchema}.
 */
public class SMSRecordReader extends AbstractDBRecordReader implements RecordReader<LongWritable, Text> {

    public static final Log LOG = LogFactory.getLog(SMSRecordReader.class.getName());

    private ParseSchema parser;
    private JobConf conf;
    private SMSInputSplit split;

    /**
     * Each relation is associated with a SQL query and schema in 
     * the job configuration. This is retrieved and a {@link ParseSchema} object
     * is created to retrieve the required fields from the result set
     * and serialize them into a delimited string.
     */
    public SMSRecordReader(SMSInputSplit split, JobConf conf) throws SQLException {

        this.split = split;
        this.conf = conf;
        parser = new ParseSchema(conf.get(SMSInputFormat.DB_QUERY_SCHEMA_PREFIX + "_" + split.getRelation()));

        setupDB(split, conf);
    }

    @Override
    protected String getSqlQuery() {
        return conf.get(SMSInputFormat.DB_SQL_QUERY_PREFIX + "_" + split.getRelation());
    }

    @Override
    public Text createValue() {
        return new Text();
    }

    /**
     * Retrieves each row from the result set, serializes it 
     * using {@link ParseSchema} and increments the number of rows
     * read in.
     * @return false if no more rows exist.
     */
    @Override
    public boolean next(LongWritable key, Text value) throws IOException {
        try {
            if (!results.next())
                return false;
            key.set(pos);
            value.set(parseResults());
            pos++;
        } catch (SQLException e) {
            throw new IOException(e);
        }
        return true;
    }

    private String parseResults() throws SQLException {
        return parser.serializeRow(results);
    }

}