@Override
  public ReturnCode filterCell(final Cell cell) {
    if (this.prefix == null) {
      return ReturnCode.INCLUDE;
    } else {
      return filterColumn(cell);
    }
  }
This filter is used for selecting only those keys with columns that matches a particular prefix.
For example, if prefix is 'an', it will pass keys with columns like 'and', 'anti' but not keys
with columns like 'ball', 'act'.
hbase-client/src/main/java/org/apache/hadoop/hbase/filter/ColumnPrefixFilter.java