Java Reference
In-Depth Information
called as an alternative to
complete
. You shouldn't call both
complete
and
completeEx-
ceptionally
on a
CompletableFuture
, though.
Example 9-14. Completing a future if there's an error
future
.
completeExceptionally
(
new
new
AlbumLookupException
(
"Unable to find "
+
name
));
A complete investigation of the
CompletableFuture
API is rather beyond the scope of this
chapter, but in many ways it is a hidden goodie bag. There are quite a few useful methods in
the API for composing and combining different instances of
CompletableFuture
in pretty
much any way imaginable. Besides, by now you should be familiar with the fluent style of
chaining sequences of higher-order functions to tell the computer what to do.
Let's take a brief look at a few of those use cases:
▪ If you want to end your chain with a block of code that returns nothing, such as a
Con-
sumer
or
Runnable
, then take a look at
thenAccept
and
thenRun
.
▪ Transforming the value of the
CompletableFuture
, a bit like using the
map
method on
Stream
, can be achieved using
thenApply
.
▪ If you want to convert situations in which your
CompletableFuture
has completed with
an exception, the
exceptionally
method allows you to recover by registering a function
to make an alternative value.
▪ If you need to do a
map
that takes account of both the exceptional case and regular use
cases, use
handle
.
▪ When trying to figure out what is happening with your
CompletableFuture
, you can use
the
isDone
and
isCompletedExceptionally
methods.
CompletableFuture
is really useful for building up concurrent work, but it's not the only
game in town. We're now going to look at a related concept that offers a bit more flexibility
in exchange for more complex code.
Reactive Programming
The concept behind a
CompletableFuture
can be generalized from single values to com-
plete streams of data using
reactive programming
. Reactive programming is actually a form
