The current implementation of SpringBootKinesisEventHandler only handles
non-aggregated events. Attempting to process aggregated events caused
ungraceful failure.
This commit fixes that by de-aggregating any events before performing
conversion. Non-aggregated events are still handled transparently.
In addition, detection of Message<T> input is performed, and
output messages are wrapped accordingly.
This results in a better experience for users because the consumer
that they write is only applied to a Flux that is subscribed to
by the framework once. It gives better control over the flow of
foos, e.g. if some component wants to subscribe on a thread.
Avoids instantiating beans if not necessary, and allows user to
provide Function as a @SpringBootApplication (for instance), or
more generally as a source to the application context (as opposed
to being component scanned).
User can switch off source or sink behaviour (the default is to bind
to input and output streams), and then configure the name of a
supplier (for a source) or consumer (for a sink).
When a Supplier<Flux<Foo>> is composed with a Function<Foo,Bar>
the resulting handler (supplier) should have Flux as its output
wrapper still (the most general output wrapper type in the chain).
A Spring Boot 2.0 app should behave the same as a Spering Boot 1.5
app with this change. The key thing was to change the return type
of the FunctionController and move the computation of single
valuedness for the output there (instead of trying to do it in the
return value handler, which isn't used in Spring 5).
Since a function is wrapper in a FluxWrapper (and possibly also
an Isolated), the link is lost between the bean and the type
metadata without this change.
Makes it possible to support other "function" types in the future.
The user is always taking a risk with the lookup that the object
returned has the generic type desired (but that hasn't changed
with this commit). FunctionCatalog is a lot simpler as a result
and also a lot more flexible.
The web module doesn't really need to depend on tomcat and all of
the Spring Boot web stack, but users need a way to grab that stuff
quickly if they want it (hence the new starter).
Also removed all spring-boot-starter dependencies from core and
context modules.
Functions with Flux and Message (as well as POJOs and Flux of POJO
which were already supported) should now work if they are created in
an isolated class loader. Preconditions:
* The class loaders must have the reactor-core (and reactive-streams)
shared between the app and the function. Practically speaking this means
there has to be a parent class loader with just reactive types, and
sibling children for the app and the function. This is not a new
requirement (it was needed for Flux of POJO anyway).
* Message types are handled reflectively, so they don't have to be in a
shared class loader. But they do have to be on the class path on
both sides (obviously).
