Java – Hive UDTF returns the ArrayList column

I am new to Hive UDTF. I have a requirement that I have to pass the string value as a Paratmeter in the UDTF, and the returned Column should be an ArrayList.

I wrote the following code:

public StructObjectInspector initialize(ObjectInspector[] arg0)
        throws UDFArgumentException {
        ArrayList<String> fieldNames = new ArrayList<String>();
        ArrayList<ObjectInspector> fieldOIs = new ArrayList<ObjectInspector>();
        fieldNames.add("col1");
        stringOI = (PrimitiveObjectInspector) arg0[0];
       listOi=(ListObjectInspector) arg0[0];
        fieldOIs.add(listOi.getListElementObjectInspector());
        return ObjectInspectorFactory.getStandardStructObjectInspector(fieldNames, fieldOIs);
}

@Override
public void process(Object[] record) throws HiveException {
     TODO Auto-generated method stub
     String document = (String) stringOI.getPrimitiveJavaObject(record[0]);
     if (document == null) {
          return;
        }
    firstColumn=(String) stringOI.getPrimitiveJavaObject(record[0]);
    secondColumn=(String) stringOI.getPrimitiveJavaObject(record[1]);
    if(outputMapper.containsKey(firstColumn))
    {

ArrayList<String> tempList=new ArrayList<String>();
        tempList=outputMapper.get(firstColumn);
        tempList.add(secondColumn);
        outputMapper.put(firstColumn,tempList);
    }
    else
    {
            childVendorList=new ArrayList<String>();
            childVendorList.add(secondColumn);
            outputMapper.put(firstColumn,childVendorList);
    }
    forward(outputMapper.get(firstColumn));

}

I get the following exception:

java.lang.ClassCastException: org.apache.hadoop.hive.serde2.lazy.objectinspector.primitive.LazyStringObjectInspector cannot be converted to org.apache.hadoop.hive.serde2.objectinspector.ListObjectInspector

Who can help???

listOi=(ListObjectInspector) arg0[0];
fieldOIs.add(listOi.getListElementObjectInspector());
return ObjectInspectorFactory.getStandardStructObjectInspector(fieldNames, fieldOIs);

This arg0[0] is a primitive object inspector. Using listOi.getListElementObjectInspector() just gives you a similar PrimitiveObjectInspector (like String, Integer is not List). It should be

fieldOIs.add(ObjectInspectorFactory.getStandardListObjectInspector(stringOI ))

This specifies the output column with a list of stringOI types.