Guardrails / java

Java toolchain is declared

java/toolchain-declared@v1

The build selects the JDK it compiles with through a Java toolchain, instead of using whichever JDK launched it.

Id	java/toolchain-declared
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/toolchain-declared@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

Let the build choose its own JDK instead of using the one that launched it:

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

A toolchain provisions the JDK it names and fails the build if it can't find one. Without it, the build compiles against whichever JDK the runner starts it with, so the same commit produces different bytecode on a machine with a different JDK installed.

More in java

• java/version-declared. The build declares the Java release it compiles for, and that release is no older than the configured floor.
• java/version-reproducible. The Java release is declared through a mechanism that provisions the JDK, not one that asks the running JDK to target an older release.

All 3 java guardrails