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Hive is a data warehouse infrastructure built on top of Hadoop see http://wiki.apache.org/hadoop/Hive

There is a newer version: 0.11.0-shark-0.9.1

/**
 * 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.hive.ql.udf;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

import org.apache.hadoop.hive.ql.exec.Description;
import org.apache.hadoop.hive.ql.exec.UDF;
import org.apache.hadoop.hive.serde2.io.TimestampWritable;
import org.apache.hadoop.io.Text;

/**
 * UDFDate.
 *
 */
@Description(name = "to_date",
    value = "_FUNC_(expr) - Extracts the date part of the date or datetime expression expr",
    extended = "Example:\n "
    + "  > SELECT _FUNC_('2009-30-07 04:17:52') FROM src LIMIT 1;\n"
    + "  '2009-30-07'")
public class UDFDate extends UDF {
  private final SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd");

  private Text t = new Text();

  public UDFDate() {
  }

  /**
   * Get the date part of a date time string.
   *
   * @param dateString
   *          the date string in the format of "yyyy-MM-dd HH:mm:ss" or
   *          "yyyy-MM-dd".
   * @return the date in the format of "yyyy-MM-dd".
   */
  public Text evaluate(Text dateString) {

    if (dateString == null) {
      return null;
    }

    try {
      Date date = formatter.parse(dateString.toString());
      t.set(formatter.format(date));
      return t;
    } catch (ParseException e) {
      return null;
    }
  }

  public Text evaluate(TimestampWritable i) {
    if (i == null) {
      return null;
    }

    t.set(formatter.format(i.getTimestamp()));
    return t;
  }

}