Autowiring implicitely Kotlin primary constructors
when there are secondary constructors has side effects
on ConstructorResolver. It seems reasonable to
require explicit @Autowired annotation in such case.
With this commit, implicit autowiring of Kotlin
primary constructors is only performed when there
is a primary constructor defined alone or with
a default constructor (define explicitly or
generated via the kotlin-noarg compiler plugin
or via optional constructor parameters with default
values).
Issue: SPR-16022
Bean-derived null values may still get passed into bean properties and injection points but only if those are declared as non-required. Note that getBean will never return null; a manual bean.equals(null) / "null".equals(bean.toString()) check identifies expected null values now. This will only ever happen with custom FactoryBeans or factory methods returning null - and since all common cases are handled by autowiring or bean property values in bean definitions, there should be no need to ever manually check for such a null value received from getBean.
Issue: SPR-15829
By using function literals with receiver, we can avoid requiring
lambda parameters for a shorter and nicer syntax. Based on a
proposal from Joseph Taylor.
Issue: SPR-15815
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
