This version is still in development and is not considered stable yet. For the latest stable version, please use Spring Framework 6.1.12! |
Null-safety
One of Kotlin’s key features is null-safety,
which cleanly deals with null
values at compile time rather than bumping into the famous
NullPointerException
at runtime. This makes applications safer through nullability
declarations and expressing “value or no value” semantics without paying the cost of wrappers, such as Optional
.
(Kotlin allows using functional constructs with nullable values. See this
comprehensive guide to Kotlin null-safety.)
Although Java does not let you express null-safety in its type-system, the Spring Framework
provides null-safety of the whole Spring Framework API
via tooling-friendly annotations declared in the org.springframework.lang
package.
By default, types from Java APIs used in Kotlin are recognized as
platform types,
for which null-checks are relaxed.
Kotlin support for JSR-305 annotations
and Spring nullability annotations provide null-safety for the whole Spring Framework API to Kotlin developers,
with the advantage of dealing with null
-related issues at compile time.
Libraries such as Reactor or Spring Data provide null-safe APIs to leverage this feature. |
You can configure JSR-305 checks by adding the -Xjsr305
compiler flag with the following
options: -Xjsr305={strict|warn|ignore}
.
For kotlin versions 1.1+, the default behavior is the same as -Xjsr305=warn
.
The strict
value is required to have Spring Framework API null-safety taken into account
in Kotlin types inferred from Spring API but should be used with the knowledge that Spring
API nullability declaration could evolve even between minor releases and that more checks may
be added in the future.
Generic type arguments, varargs, and array elements nullability are not supported yet, but should be in an upcoming release. See this discussion for up-to-date information. |