RxJava2 Nullable

Handle null value elegantly in RxJava2

Motivation

Since RxJava 2.x no longer accepts null values, but in so many cases we do need null.

For example, you get an array from some place(most time is 3rd lib), there is null value in it. Observable.fromArray(array) will throw NullPointerException. You have to do some processing like this to drop null value:

Observable.fromArray(Arrays.stream(array)
  .filter(e -> e!=null)
  .toArray(YourClass[]::new))

or do this to give a default value:

Observable.fromArray(Arrays.stream(array)
  .map(e -> e == null? defaultValue : e)
  .toArray(YourClass[]::new))

It's painful to do this handling every time we can't control the null value. (It must be 3rd party library's wrong. I hope there is no null value in the world.)

By using rx2-nullable, you can do this:

RxNullable.fromArray(array)
  .onNullDrop()
  .observable()

or

RxNullable.fromArray(array)
  .onNullWrap()
  .observable() // Observable<Optional<T>>

It gives you a easy, readable, flexible solution to null value in RxJava2.

Usage

RxNullable is the entrance. It provides following methods to create RxJava objects:

• fromArray
• fromIterable
• fromCallable
• fromPublisher
• fromFuture

They will return NullableObservableFlowable object.

Then you can set your NullHandler onto the NullableObservableFlowable. Or you can use following build-in handlers:

• onNullDrop. Drop null value.
• onNullWrap. Wrap values as Optional, you will get Observable<Optional<T>>.
• onNullDefault. Map null value to default value.
• onNullRun. When null comes, do something and drop it.

It's easy to customize your own NullHandler(But it is unnecessary in most time). For example, use a random value instead of null:

double[] array = {1d, null, 2d, null, 3d};
RxNullable.fromArray(array).observable(i -> i == null ? Math.random() : i)