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 introduces 2 new @Nullable and @NonNullApi
annotations that leverage JSR 305 (dormant but available via
Findbugs jsr305 dependency and already used by libraries
like OkHttp) meta-annotations to specify explicitly
null-safety of Spring Framework parameters and return values.
In order to avoid adding too much annotations, the
default is set at package level with @NonNullApi and
@Nullable annotations are added when needed at parameter or
return value level. These annotations are intended to be used
on Spring Framework itself but also by other Spring projects.
@Nullable annotations have been introduced based on Javadoc
and search of patterns like "return null;". It is expected that
nullability of Spring Framework API will be polished with
complementary commits.
In practice, this will make the whole Spring Framework API
null-safe for Kotlin projects (when KT-10942 will be fixed)
since Kotlin will be able to leverage these annotations to
know if a parameter or a return value is nullable or not. But
this is also useful for Java developers as well since IntelliJ
IDEA, for example, also understands these annotations to
generate warnings when unsafe nullable usages are detected.
Issue: SPR-15540
xmlunit 2.1.0 is the latest release for xmlunit.
Most of the xmlunit functionality used within spring-framework
was done through the xmlunit 1.x helper class
`org.custommonkey.xmlunit.XMLAssert`.
As of xmlunit 2.0.0 most of the XML comparison methods are done
through hamcrest matchers exposed by the xmlunit-matchers
library. In some cases during the migration, the matchers
had to be customized with custom `NodeMatcher` or
`DifferenceEvaluator` instances in order to keep the assertions
correct (they were performed with xmlunit 1.x previously).
Issue: SPR-14043
This commit adds a test runtime dependency on log4j 2 for every project
and migrates all log4j.properties files to log4j2-test.xml files.
Issue: SPR-14431
This commit migrates all remaining tests from JUnit 3 to JUnit 4, with
the exception of Spring's legacy JUnit 3.8 based testing framework that
is still in use in the spring-orm module.
Issue: SPR-13514
Juergen Hoeller
Sebastien Deleuze
Sam Brannen
Marius Grama
Stephane Nicoll
Johnny Lim
Rossen Stoyanchev
Juergen Hoeller
Stephane Nicoll