Closing over immutable variable and accumulate values across multiple iterations as a lambda expression - Java 8

Question

WebTarget in Jersey client is implemented as a immutable object, and any operations to change the state returns a new WebTarget. To add query params to it, which is coming in as

Answer 1

If you want functional approach you need foldLeft(right) or reduce.

foldLeft is implemented in some libraries, for example Functionaljava and streamEx.

Functionaljava:

<B> B foldLeft(final F<B, F<A, B>> bff, final B z)

WebTarget wt = wtCollection.foldLeft(x -> (y -> x.queryParam(...)), new WebTarget());

StreamEx:

<U> U foldLeft(U seed, BiFunction<U, ? super T, U> accumulator) 

UPD stream-reduce

queryMap.entrySet().stream()
    .reduce(new WebTarget(), (x, y) -> { 
        x.queryParam(y.getKey(), y.getValue()); 
    });

Answer 2

You can use the ol' array trick, which is not good for anything more than a proof of concept.

WebTarget[] webTarget = {client.target(this.address.getUrl()).path(path)};
if (queryMap != null){
    queryMap.forEach((k, v)->{
        webTarget[0] =  webTarget[0].queryParam(k, v);
    });
}
return webTarget[0];

You could improve it by using an AtomicReference.

AtomicReference<WebTarget> webTarget = new AtomicReference<>(client.target(this.address.getUrl()).path(path));
if (queryMap != null){
    queryMap.forEach((k, v)->{
        webTarget.updateAndGet(w->w.queryParam(k, v));
    });
}
return webTarget.get();