Guardrails / java

Java version is reproducible

java/version-reproducible@v1

The Java release is declared through a mechanism that provisions the JDK, not one that asks the running JDK to target an older release.

Id	java/version-reproducible
Version	v1
Category	java
Default severity	warning
Interpreter	python3
Timeout	30 seconds
Violations tolerated	0
Collects	java

Collectors

This guardrail doesn't gather anything itself. It relies on the collectors below, which the CLI runs once per build before any check, and reads what they found from GUARDRAIL_FACTS. If a collector collects nothing, this guardrail is skipped, not failed.

Collector	Gathers	Inputs it is given
java	The Java version the Gradle or Maven build declares, how it declares it, and whether that mechanism makes the build reproducible, for the project and for every Gradle project it includes.	projectDir

The inputs above are this guardrail's own inputs, passed straight through to the collector. Setting one in buildnote.json changes what is collected, and two guardrails configured the same way share a single collection.

Configuration

{
  "guardrails": {
      "failOn": "error",
      "checks": [
          {
              "use": "java/version-reproducible@v1",
              "severity": "warning",
              "with": {
                  "projectDir": "."
              },
              "exemptions": []
          }
      ]
  }
}

Inputs

Input	Description	Default	Environment variable
projectDir	Directory holding the project, relative to the directory the CLI runs in.	.	GUARDRAIL_INPUT_PROJECTDIR

How to fix

Replace sourceCompatibility, targetCompatibility, options.release or maven.compiler.release with a toolchain. A toolchain selects the JDK itself, instead of asking the running one to target an older release:

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

With sourceCompatibility = JavaVersion.VERSION_17, the build still compiles against the class library of whichever JDK is on the runner. A method added after Java 17 resolves at compile time, then throws NoSuchMethodError on the Java 17 runtime the artifact was built for.

More in java

• java/toolchain-declared. The build selects the JDK it compiles with through a Java toolchain, instead of using whichever JDK launched it.
• java/version-declared. The build declares the Java release it compiles for, and that release is no older than the configured floor.

All 3 java guardrails