Create the UDF class

You define the UDF logic in a new class that returns the data type of a selected column in a table.

1. In IntelliJ, click the vertical project tab, and expand hiveudf: hiveudf > src > main. Select the java directory, and on the context menu, select New > Java Class and name the class, for example, TypeOf.
2. Extend the GenericUDF class to include the logic that identifies the data type of a column.
   For example:

   package com.mycompany.hiveudf;
   
   import org.apache.hadoop.hive.ql.exec.UDFArgumentException;
   import org.apache.hadoop.hive.ql.metadata.HiveException;
   import org.apache.hadoop.hive.ql.udf.generic.GenericUDF;
   import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspector;
   import org.apache.hadoop.hive.serde2.objectinspector.primitive.PrimitiveObjectInspectorFactory;
   import org.apache.hadoop.io.Text;
   
   public class TypeOf extends GenericUDF {
     private final Text output = new Text();
   
   @Override
     public ObjectInspector initialize(ObjectInspector[] arguments) throws UDFArgumentException {
       checkArgsSize(arguments, 1, 1);
       checkArgPrimitive(arguments, 0);
       ObjectInspector outputOI = PrimitiveObjectInspectorFactory.writableStringObjectInspector;
       return outputOI;
     }
   
   @Override
     public Object evaluate(DeferredObject[] arguments) throws HiveException {
       Object obj;
       if ((obj = arguments[0].get()) == null) {
         String res = "Type: NULL";
         output.set(res);
         } else {
         String res = "Type: " + obj.getClass().getName();
         output.set(res);
       }
       return output;
     }
   
   @Override
     public String getDisplayString(String[] children) {
       return getStandardDisplayString("TYPEOF", children, ",");
     }
   }