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https://github.com/jasongoodwin/better-java-monads


https://github.com/jasongoodwin/better-java-monads

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README 

        
better-java8-monads

==================



This library was built immediately after Java8 became GA to help fill in some blanks (Try, Futures.sequence)

There are some other libraries mentioned w/ this project on Stack Overflow: https://stackoverflow.com/questions/27787772/try-monad-in-java-8



Feature Overview

----------------



*Try* - Optional exists to express nulls in types, but there is no way to express success/failure in types. Try to the rescue! The Try type is very similar to the Try in Scala's standard lib.



*CompletableFuture.sequence* - If you have a list of futures, there is no obvious way to get a future of a list. This will come in handy!



Usage

=====



Import into your project:



SBT

---



    "com.jason-goodwin" % "better-monads" % "0.4.0"



Maven

-----



    

	    com.jason-goodwin

	    better-monads

	    0.4.0

    



Try

===



The try monad was attributed to Twitter and placed into the Scala standard library.

While both Scala and Haskell have a monad Either which has a left and a right type, 

a Try is specifically of a type T on success or an exception on failure.



Usage

-----



The Try api is meant to be similar to the Optional type so has the same functions.

- get() returns the held value or throws the thrown exception

- getUnchecked() returns the held value or throws the thrown exception wrapped in a RuntimeException instance

- map(x) maps the success value x to a new value and type or otherwise passes the Failure forward.

- flatMap((x) -> f(x)) maps the success value x to a new Try of f(x).

- recover((t) -> x) will return the success value of the Try in the success case or the value x in the failure case. Exposes the exception.

- recoverWith((t) -> f(x)) will return the success value of the Try in the success case or a new try of f(x) in the failure case. Exposes the exception.

- filter((x) -> isTrue(x)) - If Success, returns the same Success if the predicate succeeds, otherwise, returns a Failure with type NoSuchElementException.

- onSuccess((x) -> f(x)) execute some code on success - takes Consumer (eg requires no return value).

- onFailure((x) -> f(x)) execute some code on failure - takes Consumer (eg requires no return value).

- orElse(x) will return the success value of the Try in success case or the value x in failure case.

- orElseTry(f) will return the success value of the Try in success case or a new Try(f) in the failure case.

- orElseThrow(() -> throw new T) gets result or on failure will throw checked exception of type T

- toOptional() will return Optional of success value of Try (if not null), otherwise it will return an empty Optional



Futures

=======

There is no sequence method in the Java8 library so I've provided one. You'll find the function Futures.sequence which will convert a `List>` into a `CompletableFuture>`. This is useful in the common use case of processing all of the elements of a list concurrently.



Usage

-----

Simply call Futures.sequence on a `List>` to get back a single future with the list of your items.



    List list = IntStream.range(0, 100).boxed().collect(Collectors.toList());

        int size = list.size();

        List> futures = list

                .stream()

                .map(x -> CompletableFuture.supplyAsync(() -> x))

                .collect(Collectors.toList());



    CompletableFuture> futureList = Futures.sequence(futures);



Tests

=====



See the tests for examples of all functionality.