如何链接到Java 8供应商

Question

Supplier does not provide a andThen method, so chaining another Function to the result of a Supplier is not possible. Is the only alternative to use a Function<Void, R> that does not get any parameter?

In other words, if Supplier.andThen() existed I could write:

 Supplier<Exception> cleanedExceptionSupplier = exceptionSupplier.andThen( 
     e -> clean(e));

Since it does not exist, how can I cleanly implement cleanedExceptionSupplier ?

Answer 1

Instead of:

 Supplier<T> supp2 = supp1.andThen(function);

(which, uses a method you've seen doesn't exist)

... you could use:

 Supplier<T> supp2 = () -> function.apply(supp1.get());

Answer 2

Just adding my alternate solution as a candidate here

Function<Void, R> supplierAsFunction = v -> returnSomethingOfR();

supplierAsFunction.andThen(function).apply(null); 

Applying null as a parameter is rather ugly but this solution maintains functional style while using only java.util.function classes.

Answer 3

You may use CompletableFuture.supplyAsync(supplier) . Having supplier that supplies object of type SomeType you will get CompletableFuture<SomeType> .

Having CompletableFuture you may chain it using methods thenAccept , thenApply and other.

As a side effect, your program will become more reactive. calling supplyAsync will not block. Actualy, you may never block as long as you will not call blocking operation on your CompletableFuture .

To I would solve your case as follows:

Supplier<Exception> cleanedExceptionSupplier=<some way to get supplier>.
CompletableFuture.supplyAsync(cleanedExceptionSupplier).thenAccept(exception -> System.out.println(exception.toString());

Side note: it does not look right to me to have Supplier of Exception . Is exception indeed main effect you want to supply? Or is it (possibly unwanted) corner case?