Gradle "invalid source release" / "release version not supported"

By Daniel Zoghalchali·Latchkey

The Java compiler Gradle invoked is older than the language level you asked for. A JDK 17 cannot compile sourceCompatibility = 21 - it does not support that release.

What this error means

Compilation fails with invalid source release: 21 or error: release version 21 not supported. The number is what your build requests; the compiling JDK is older than it.

gradle output

> Task :app:compileJava FAILED
error: invalid source release: 21
# or, with --release:
error: release version 21 not supported

Common causes

Compile JDK older than the requested release

A sourceCompatibility/targetCompatibility or release set to 21 needs a JDK 21 compiler. The JDK Gradle is using is older, so the language level is unsupported.

No Java toolchain pinned

Without a java.toolchain block, Gradle compiles with whatever JDK runs Gradle. If that is older than your target, the source release is invalid.

How to fix it

Pin a Java toolchain

Let Gradle select (and download) a JDK that matches your target, independent of the JDK running Gradle.

build.gradle.kts

java {
    toolchain {
        languageVersion = JavaLanguageVersion.of(21)
    }
}

Provision the matching JDK in CI

Ensure a JDK 21 is available for the toolchain to resolve.

.github/workflows/ci.yml

- uses: actions/setup-java@v4
  with:
    distribution: temurin
    java-version: '21'

How to prevent it

Use a Java toolchain so the compile JDK is explicit and reproducible.
Provision the toolchain JDK in CI with setup-java.
Keep languageVersion aligned with an available JDK.

Frequently asked questions

What causes ""invalid source release""?

A sourceCompatibility/targetCompatibility or release set to 21 needs a JDK 21 compiler. The JDK Gradle is using is older, so the language level is unsupported.

How do I fix "invalid source release"?