org.apache.hadoop.mapreduce.lib.db.DataDrivenDBRecordReader.java Source code

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Here is the source code for org.apache.hadoop.mapreduce.lib.db.DataDrivenDBRecordReader.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.mapreduce.lib.db;

import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
import java.sql.Connection;
import java.sql.DatabaseMetaData;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;

import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Writable;
import org.apache.hadoop.mapreduce.InputFormat;
import org.apache.hadoop.mapreduce.InputSplit;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.JobContext;
import org.apache.hadoop.mapreduce.RecordReader;
import org.apache.hadoop.mapreduce.TaskAttemptContext;
import org.apache.hadoop.util.ReflectionUtils;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.conf.Configurable;
import org.apache.hadoop.conf.Configuration;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * A RecordReader that reads records from a SQL table,
 * using data-driven WHERE clause splits.
 * Emits LongWritables containing the record number as
 * key and DBWritables as value.
 */
@InterfaceAudience.Public
@InterfaceStability.Evolving
public class DataDrivenDBRecordReader<T extends DBWritable> extends DBRecordReader<T> {

    private static final Logger LOG = LoggerFactory.getLogger(DataDrivenDBRecordReader.class);

    private String dbProductName; // database manufacturer string.

    /**
     * @param split The InputSplit to read data for
     * @throws SQLException 
     */
    public DataDrivenDBRecordReader(DBInputFormat.DBInputSplit split, Class<T> inputClass, Configuration conf,
            Connection conn, DBConfiguration dbConfig, String cond, String[] fields, String table, String dbProduct)
            throws SQLException {
        super(split, inputClass, conf, conn, dbConfig, cond, fields, table);
        this.dbProductName = dbProduct;
    }

    /** Returns the query for selecting the records,
     * subclasses can override this for custom behaviour.*/
    @SuppressWarnings("unchecked")
    protected String getSelectQuery() {
        StringBuilder query = new StringBuilder();
        DataDrivenDBInputFormat.DataDrivenDBInputSplit dataSplit = (DataDrivenDBInputFormat.DataDrivenDBInputSplit) getSplit();
        DBConfiguration dbConf = getDBConf();
        String[] fieldNames = getFieldNames();
        String tableName = getTableName();
        String conditions = getConditions();

        // Build the WHERE clauses associated with the data split first.
        // We need them in both branches of this function.
        StringBuilder conditionClauses = new StringBuilder();
        conditionClauses.append("( ").append(dataSplit.getLowerClause());
        conditionClauses.append(" ) AND ( ").append(dataSplit.getUpperClause());
        conditionClauses.append(" )");

        if (dbConf.getInputQuery() == null) {
            // We need to generate the entire query.
            query.append("SELECT ");

            for (int i = 0; i < fieldNames.length; i++) {
                query.append(fieldNames[i]);
                if (i != fieldNames.length - 1) {
                    query.append(", ");
                }
            }

            query.append(" FROM ").append(tableName);
            if (!dbProductName.startsWith("ORACLE")) {
                // Seems to be necessary for hsqldb? Oracle explicitly does *not*
                // use this clause.
                query.append(" AS ").append(tableName);
            }
            query.append(" WHERE ");
            if (conditions != null && conditions.length() > 0) {
                // Put the user's conditions first.
                query.append("( ").append(conditions).append(" ) AND ");
            }

            // Now append the conditions associated with our split.
            query.append(conditionClauses.toString());

        } else {
            // User provided the query. We replace the special token with our WHERE clause.
            String inputQuery = dbConf.getInputQuery();
            if (inputQuery.indexOf(DataDrivenDBInputFormat.SUBSTITUTE_TOKEN) == -1) {
                LOG.error("Could not find the clause substitution token " + DataDrivenDBInputFormat.SUBSTITUTE_TOKEN
                        + " in the query: [" + inputQuery + "]. Parallel splits may not work correctly.");
            }

            query.append(inputQuery.replace(DataDrivenDBInputFormat.SUBSTITUTE_TOKEN, conditionClauses.toString()));
        }

        LOG.debug("Using query: " + query.toString());

        return query.toString();
    }
}