@Override
            public void addFloat(final float value) {
              HiveDecimalWritable decimalWritable = new HiveDecimalWritable();
              decimalWritable.setFromDouble(value);
              parent.set(index, HiveDecimalUtils
                  .enforcePrecisionScale(decimalWritable, (DecimalTypeInfo) hiveTypeInfo));
            }
ETypeConverter is an easy way to set the converter for the right type.
ql/src/java/org/apache/hadoop/hive/ql/io/parquet/convert/ETypeConverter.java