JavaPairRDD<String, Tuple2<SomeModelClass, Optional<SomeModelClass>>> join = RDD1.leftOuterJoin(RDD2);

    JavaRDD<SomeModelClass> joinMap = join
            .map(tuple -> {
                Tuple2<SomeModelClass, Optional<SomeModelClass>> _2 = tuple._2();
                SomeModelClass RDD1 = _2._1();
                Optional<SomeModelClass> RDD2 = _2._2();
                SomeModelClass SomeModelClass = new SomeModelClass();

      if(!RDD1.ispresent && someColumn==y){
              //join with RDD3 get some values
              return results
          } else

      //join with some other RDDD


                return SomeModelClass;
            });