content: package com.github.aaronshan.functions.array;
  
  import org.apache.hadoop.hive.ql.exec.Description;
  import org.apache.hadoop.hive.ql.exec.UDFArgumentException;
  import org.apache.hadoop.hive.ql.exec.UDFArgumentLengthException;
  import org.apache.hadoop.hive.ql.exec.UDFArgumentTypeException;
  import org.apache.hadoop.hive.ql.metadata.HiveException;
  import org.apache.hadoop.hive.ql.udf.generic.GenericUDF;
  import org.apache.hadoop.hive.serde2.objectinspector.ListObjectInspector;
  import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspector;
  import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspectorUtils;
  import org.apache.hadoop.hive.serde2.objectinspector.primitive.PrimitiveObjectInspectorFactory;
  import org.apache.hadoop.io.IntWritable;
  
  /**
   * @author ruifeng.shan
   * date: 2016-07-27
   * time: 10:09
   */
  @Description(name = "array_element_at"
          , value = "_FUNC_(array<E>, index) - returns element of array at given index. If index < 0, element_at accesses elements from the last to the first."
          , extended = "Example:\n > select _FUNC_(array, index) from src;")
  public class UDFArrayElementAt extends GenericUDF {
  
      private static final int ARRAY_IDX = 0;
      private static final int INDEX_IDX = 1;
      private static final int ARG_COUNT = 2; // Number of arguments to this UDF
      private transient ObjectInspector indexOI;
      private transient ListObjectInspector arrayOI;
      private transient ObjectInspector arrayElementOI;
  
      public UDFArrayElementAt() {
  
      }
  
      @Override
      public ObjectInspector initialize(ObjectInspector[] arguments) throws UDFArgumentException {
          // Check if two arguments were passed
          if (arguments.length != ARG_COUNT) {
              throw new UDFArgumentLengthException(
                      "The function array_element_at(array, index) takes exactly " + ARG_COUNT + " arguments.");
          }
  
          // Check if ARRAY_IDX argument is of category LIST
          if (!arguments[ARRAY_IDX].getCategory().equals(ObjectInspector.Category.LIST)) {
              throw new UDFArgumentTypeException(ARRAY_IDX,
                      "\"" + org.apache.hadoop.hive.serde.serdeConstants.LIST_TYPE_NAME + "\" "
                              + "expected at function array_element_at, but "
                              + "\"" + arguments[ARRAY_IDX].getTypeName() + "\" "
                              + "is found");
          }
  
          arrayOI = (ListObjectInspector) arguments[ARRAY_IDX];
          arrayElementOI = arrayOI.getListElementObjectInspector();
          indexOI = arguments[INDEX_IDX];
  
          ObjectInspector expectOI = PrimitiveObjectInspectorFactory.writableIntObjectInspector;
  
          // Check if index and expect are of same type
          if (!ObjectInspectorUtils.compareTypes(expectOI, indexOI)) {
              throw new UDFArgumentTypeException(INDEX_IDX,
                      "\"" + expectOI.getTypeName() + "\""
                              + " expected at function array_element_at, but "
                              + "\"" + indexOI.getTypeName() + "\""
                              + " is found");
          }
  
          return arrayElementOI;
      }
  
      @Override
      public Object evaluate(DeferredObject[] arguments) throws HiveException {
          Object array = arguments[ARRAY_IDX].get();
          IntWritable index = (IntWritable) arguments[INDEX_IDX].get();
  
          int arrayLength = arrayOI.getListLength(array);
  
          // Check if array is null or empty or index is null
          if (index == null || arrayLength <= 0) {
              return null;
          }
  
          if (index.get() < 0) {
              int idx = arrayLength + index.get();
              if (idx >= 0) {
                  return arrayOI.getListElement(array, idx);
              }
          } else {
              if (index.get() < arrayLength) {
                  return arrayOI.getListElement(array, index.get());
              }
          }
  
          return null;
      }
  
      @Override
      public String getDisplayString(String[] strings) {
          assert (strings.length == ARG_COUNT);
          return "array_element_at(" + strings[ARRAY_IDX] + ", "
                  + strings[INDEX_IDX] + ")";
      }
  }