Usage of stream in java8 for multiple get methods

Question

String serviceClass = railsComponent
    .getRailOffer()
    .getRailProducts()
    .get( 0 )
    .getRailProduct()
    .getFareBreakdownList()
    .get( 0 )
    .getPassengerFareList()
    .get( 0 )
    .getPassengerSegmentFareList()
    .get( 0 )
    .getCarrierServiceClassDisplayName();

this returns me valid serviceClass value.

I wanted to convert this code with the help of java8 stream concept.

I tried with below

String serviceClass = railsComponent.getRailOffer().getRailProducts().stream()
                .map(railProcucts -> railProcucts.getRailProduct().getFareBreakdownList().stream()
                .map(fareBreakdownType -> fareBreakdownType.getPassengerFareList().stream()
                .map(passengerFareType -> passengerFareType.getPassengerSegmentFareList().stream()
                .map(segmentFareType -> segmentFareType.getCarrierServiceClassDisplayName())))).findFirst().orElse(null).toString();

which is returning me value as java.util.stream.ReferencePipeline$3@5585427d .

Can someone tell me what am I doing wrong and how I get proper value in this case.

Not that it's what you asked but the null case here is absolutely going to throw a `NullPoiinterException` at you if you call `toString()` on null. `findFirst().orElse(null).toString();` — Todd, Jun 16 '17 at 13:46
I wanted to avoid multiple null checks. so trying to use this. — Rocker rock, Jun 16 '17 at 13:49
@MikeAdamenko because it was almost the answer in [this post](https://stackoverflow.com/questions/44583350/multiple-null-checks-handling-in-java8). He don't get the difference between Stream an Optionnal — AxelH, Jun 16 '17 at 13:50
Then you want [`Optional.ofNullable`](https://docs.oracle.com/javase/8/docs/api/java/util/Optional.html#ofNullable-T-), not a stream. — khelwood, Jun 16 '17 at 13:50
Why do you think you need to use a `Stream` here? I think your first attempt is a lot cleaner and a lot nicer. — Joe C, Jun 17 '17 at 16:03

score 2 · Accepted Answer · answered Jun 19 '17 at 09:43

You are using here map instead of flatMap, so you should use:

railsComponent.getRailOffer().getRailProducts().stream()
    .flatMap(rp -> rp.getFareBreakdownList().stream())
    .flatMap(fb -> fbl.getPassengerFareList().stream())
    .flatMap(pf -> pfl.getPassengerSegmentFareList().stream())
    .map(psf -> psf.getCarrierServiceClassDisplayName())
    .findFirst()
    .orElse(null);

Be aware that will return String or null, so you cannot just add toString() without check.

Usage of stream in java8 for multiple get methods

1 Answers1