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package org.apache.hadoop.hive.ql.udf.generic;

import org.apache.hadoop.hive.ql.exec.UDFArgumentException;
import org.apache.hadoop.hive.ql.metadata.HiveException;
import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspector;
import org.apache.hadoop.hive.serde2.objectinspector.StructObjectInspector;

/**
 * A Generic User-defined Table Generating Function (UDTF)
 * 
 * Generates a variable number of output rows for a single input row. Useful for
 * explode(array)...
 */

public abstract class GenericUDTF {
  Collector collector = null;

  /**
 * Initialize this GenericUDTF. This will be called only once per instance.
 * 
 * @param args
 *          An array of ObjectInspectors for the arguments
 * @return A StructObjectInspector for output. The output struct represents a
 *         row of the table where the fields of the stuct are the columns. The
 *         field names are unimportant as they will be overridden by user
 *         supplied column aliases.
   */
  public abstract StructObjectInspector initialize(ObjectInspector[] argOIs)
      throws UDFArgumentException;

  /**
 * Give a set of arguments for the UDTF to process.
 * 
 * @param o
 *          object array of arguments
   */
  public abstract void process(Object[] args) throws HiveException;

  /**
 * Called to notify the UDTF that there are no more rows to process.
 * Clean up code or additional forward() calls can be made here.
   */
  public abstract void close() throws HiveException;

  /**
 * Associates a collector with this UDTF. Can't be specified in the
 * constructor as the UDTF may be initialized before the collector has been
 * constructed.
 * 
 * @param collector
   */
  public final void setCollector(Collector collector) {
    this.collector = collector;
  }

  /**
 * Passes an output row to the collector.
 * 
 * @param o
 * @throws HiveException
   */
  protected final void forward(Object o) throws HiveException {
    collector.collect(o);
  }

}