39 lines
2.1 KiB
Plaintext
39 lines
2.1 KiB
Plaintext
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[[kotlin-null-safety]]
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= Null-safety
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One of Kotlin's key features is https://kotlinlang.org/docs/reference/null-safety.html[null-safety],
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which cleanly deals with `null` values at compile time rather than bumping into the famous
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`NullPointerException` at runtime. This makes applications safer through nullability
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declarations and expressing "`value or no value`" semantics without paying the cost of wrappers, such as `Optional`.
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(Kotlin allows using functional constructs with nullable values. See this
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https://www.baeldung.com/kotlin-null-safety[comprehensive guide to Kotlin null-safety].)
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Although Java does not let you express null-safety in its type-system, the Spring Framework
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provides <<core#null-safety, null-safety of the whole Spring Framework API>>
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via tooling-friendly annotations declared in the `org.springframework.lang` package.
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By default, types from Java APIs used in Kotlin are recognized as
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https://kotlinlang.org/docs/reference/java-interop.html#null-safety-and-platform-types[platform types],
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for which null-checks are relaxed.
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https://kotlinlang.org/docs/reference/java-interop.html#jsr-305-support[Kotlin support for JSR-305 annotations]
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and Spring nullability annotations provide null-safety for the whole Spring Framework API to Kotlin developers,
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with the advantage of dealing with `null`-related issues at compile time.
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NOTE: Libraries such as Reactor or Spring Data provide null-safe APIs to leverage this feature.
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You can configure JSR-305 checks by adding the `-Xjsr305` compiler flag with the following
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options: `-Xjsr305={strict|warn|ignore}`.
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For kotlin versions 1.1+, the default behavior is the same as `-Xjsr305=warn`.
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The `strict` value is required to have Spring Framework API null-safety taken into account
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in Kotlin types inferred from Spring API but should be used with the knowledge that Spring
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API nullability declaration could evolve even between minor releases and that more checks may
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be added in the future.
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NOTE: Generic type arguments, varargs, and array elements nullability are not supported yet,
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but should be in an upcoming release. See https://github.com/Kotlin/KEEP/issues/79[this discussion]
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for up-to-date information.
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