@Override
  public Predicate toPredicate(String prop, String val) throws InvalidQueryException {
    if (val == null) {
      throw new InvalidQueryException("Filter operator is missing a required right operand.");
    }
    return new FilterPredicate(prop, val);
  }
This is a binary operator which takes right operand as a regular
expression and applies it to the left operand
ambari-server/src/main/java/org/apache/ambari/server/api/predicate/operators/FilterOperator.java