@Override
    public void readFields(DataInput in) throws IOException {
      primitiveCategory = WritableUtils.readEnum(in,
          PrimitiveObjectInspector.PrimitiveCategory.class);
      typeName = WritableUtils.readString(in);
      try {
        primitiveJavaType = Class.forName(WritableUtils.readString(in));
        primitiveJavaClass = Class.forName(WritableUtils.readString(in));
        primitiveWritableClass = Class.forName(WritableUtils.readString(in));
      } catch (ClassNotFoundException e) {
        throw new IOException(e);
      }
    }
typeName is the name of the type as in DDL.
serde/src/java/org/apache/hadoop/hive/serde2/objectinspector/primitive/PrimitiveObjectInspectorUtils.java