How to flatmap a stream of streams in Java?

I want to transform the stream of streams of objects to a single stream of objects. I know that I have to use the flatMap method, but I'm not able to achieve that, look at:

Stream<Stream<Object>> objectStreams = ...
Stream<Object> flatMappedStream = objectStreams.flatMap( ... );

Could anyone please help me?

Basically, you want to concatenate all the nested streams into one flat stream, without affecting the members themselves. You'll use

objectStreams.flatMap(Function.identity());

because you must provide some mapping function for each stream member, and in this case it is the identity function.