As a follow-up of the ApplicationContext Kotlin extensions, close to
the Kotlin functional WebFlux DSL and partially inspired of the
Groovy/Scala bean configuration DSL, this commit introduces a
lightweight Kotlin DSL for functional bean declaration.
It allows declaring beans as following:
beans {
bean<Foo>()
profile("bar") {
bean<Bar>("bar", scope = Scope.PROTOTYPE)
}
environment({ it.activeProfiles.contains("baz") }) {
bean { Baz(it.ref()) }
bean { Baz(it.ref("bar")) }
}
}
Advantages compared to Regular ApplicationContext API are:
- No exposure of low-level ApplicationContext API
- Focused DSL easier to read, but also easier to write with a fewer
entries in the auto-complete
- Declarative syntax instead of functions with verbs like registerBeans
while still allowing programmatic registration of beans if needed
- Such DSL is idiomatic in Kotlin
- No need to have an ApplicationContext instance to write how you
register your beans since beans { } DSL is conceptually a
Consumer<GenericApplicationContext>
This DSL effectively replaces ApplicationContext Kotlin extensions as
the recommended way to register beans in a functional way with Kotlin.
Issue: SPR-15755
This commit also removes nullability from two common spots: ResolvableType.getType() and TargetSource.getTarget(), both of which are never effectively null with any regular implementation. For such scenarios, a non-null empty type/target is the cleaner contract.
Issue: SPR-15540
Beyond just formally declaring the current behavior, this revision actually enforces non-null behavior in selected signatures now, not tolerating null values anymore when not explicitly documented. It also changes some utility methods with historic null-in/null-out tolerance towards enforced non-null return values, making them a proper citizen in non-null assignments.
Some issues are left as to-do: in particular a thorough revision of spring-test, and a few tests with unclear failures (ignored as "TODO: NULLABLE") to be sorted out in a follow-up commit.
Issue: SPR-15540
This commit improves `AbstractValueAdaptingCache` to throw a dedicated
exception if `allowNullValues` is `false` and a `null` value is provided
anyway. This avoid a lower-level exception from the cache library that
will miss some context.
Issue: SPR-15173
Put the lambda parameter at the end and use a function
instead of a supplier to be able to register beans like this:
val context = GenericApplicationContext()
context.registerBean(Foo::class)
context.registerBean{ Bar(it.getBean(Foo::class)) }
Issue: SPR-15118
Based on an idea from Mario Arias, we can avoid requiring specifying
explicitly Supplier lambda type in Kotlin API by declaring the supplier
parameter as "crossinline supplier: () -> T" instead of
"supplier: Supplier<T>".
Issue: SPR-15118
