v3.8.0

Reactor Core 3.8.0 is part of 2025.0.0 Release Train.

3.8.0 Highlights

Enhanced Null Safety using JSpecify

🦺 Reactor Core 3.8.0 introduces JSpecify annotations for comprehensive null safety, replacing the legacy JSR 305-based annotations with a modern, properly specified standard that prevents NullPointerExceptions through build-time checks. This upgrade provides enhanced IDE support, seamless Kotlin integration with automatic translation to Kotlin's null safety system, and more precise nullability declarations including support for arrays, varargs, and generic types — making Reactor APIs safer and more developer-friendly across the entire ecosystem.

⚠️ Nullability annotations from reactor.util.annotation have been deprecated in favour of JSpecify annotations.

📖 Check the refreshed reference documentation section on Null Safety.

⚠️ Note for Kotlin users: While this change is backwards compatible in the Java ecosystem and does not dictate a new generation of Reactor Core, we do appreciate it can appear as breaking changes for Kotlin codebases. The benefits are well defined nullness of the Reactor API and reduction of the ceremony that was required prior to the introduction of JSpecify annotations.

Repeat Spec

Repeat functionality from Reactor Addons has been ported to Reactor Core under the RepeatSpec class and can be used in conjunction with the Flux#repeatWhen() and Mono#repeatWhen() operators. Make sure to check out the Javadoc.

Reactor Core Micrometer version aligned with Reactor Core version

The reactor-core-micrometer library, which is part of the reactor-core repository is always released together with reactor-core, hence we decided to align their versions starting from 3.8.0 (the previous line was 1.2.x corresponding with 3.7.x of reactor-core).

What's Changed

⚠️ Update considerations and deprecations

• Introduce JSpecify for nullability annotations by @​chemicL in reactor/reactor-core#4091

✨ New features and improvements

• Bump byteBuddy from 1.17.7 to 1.17.8 by @​dependabot[bot] in reactor/reactor-core#4113
• Bump io.projectreactor.tools:blockhound from 1.0.14.RELEASE to 1.0.15.RELEASE by @​dependabot[bot] in reactor/reactor-core#4120
• Bump Micrometer to 1.16.0 by @​chemicL in fedfdd2549fe1190ec5e1b14a13ddf24a1f1b75f
• Bump Context Propagation to 1.2.0 by @​chemicL in fedfdd2549fe1190ec5e1b14a13ddf24a1f1b75f
• Repeat specification for use with repeatWhen operator by @​kwondh5217 in reactor/reactor-core#4027 and refinement by @​chemicL in b313f5781b919a30bd8b7316438610fbe02b38b7
• Add Hooks#isAutomaticContextPropagationEnabled by @​sdeleuze in reactor/reactor-core#4090
• Adjust reactor.util.Logger vararg nullability by @​chemicL in reactor/reactor-core#4098
• Adjust Mono methods: fromCallable and fromSupplier nullability by @​chemicL in reactor/reactor-core#4116
• Address NullAway warnings and refine StepVerifier nullability by @​chemicL in reactor/reactor-core#4126
• Nullaway jspecify mode fixes by @​chemicL in reactor/reactor-core#4127
• Refine StepVerifier nullability reflecting non-null Publisher values by @​chemicL in reactor/reactor-core#4132
• Unify reactor-core-micrometer version with reactor-core by @​chemicL in reactor/reactor-core#4136

🐞 Bug fixes

• Fix RetryBackoffSpec multiplier handling of fractional values by @​chemicL in reactor/reactor-core#4048
• Adjust Flux#map mapper to disallow null return values by @​chemicL in reactor/reactor-core#4103

📖 Documentation

• [docs] Add Null Safety documentation by @​chemicL in reactor/reactor-core#4137
• Add more description on tap operator by @​ttddyy in reactor/reactor-core#4009
• fix doc title displayed as untitled by @​dev-jonghoonpark in reactor/reactor-core#4008

New Contributors