java_toolchains

Non-LTS JDK toolchains for Bazel, packaged as a standalone bzlmod module on top of rules_java.

rules_java ships remote JDK toolchains for the LTS line (8, 11, 17, 21, 25) and is deliberately conservative about carrying non-LTS releases, since each one is only supported for six months. This module adds those short-lived releases (currently JDK 27) without forking rules_java: it reuses rules_java's own remote_java_repository, default_java_toolchain, and java_runtime_version_alias machinery and only contributes the archive catalog.

What it provides

• Runtime toolchains for JDK 27 across linux (x86_64/aarch64/ppc64le/riscv64/s390x), macOS (x86_64/aarch64), and Windows (x86_64), selectable with --java_runtime_version=remotejdk_27 (or =27).
• @java_toolchains//toolchains:remotejdk_27 — the runtime label, for use as a java_runtime = ... attribute.
• @java_toolchains//toolchains:toolchain_jdk_27 — a compile toolchain that runs javac on JDK 27, selectable with --java_language_version=27. (The LTS toolchains top out at JDK 25, whose javac rejects source/target 27.)

Usage

This module is not yet released or published to the Bazel Central Registry. For now, add a Git override pinned to a commit whose module name is java_toolchains:

# MODULE.bazel
bazel_dep(name = "rules_java", version = "9.9.0")
bazel_dep(name = "java_toolchains", version = "0.0.1")
git_override(
    module_name = "java_toolchains",
    remote = "https://github.com/davido/java_toolchains.git",
    commit = "5ba7b4f08019bccab1f560f29d1734ed55e3e985",
)

# .bazelrc
build:java27 --java_language_version=27
build:java27 --java_runtime_version=remotejdk_27
build:java27 --tool_java_language_version=27
build:java27 --tool_java_runtime_version=remotejdk_27

bazelisk build --config=java27 //...

After a release is admitted to the BCR, the Git override can be removed.

Example

examples/consuming is a self-contained workspace that consumes this module via local_path_override and builds a Java target at language level 27:

cd examples/consuming
bazelisk run --config=java27 //:hello   # prints "Hello from JDK 27"
bazelisk test --config=java27 //:toolchain_test

The test checks JDK 27 execution and Java 27 bytecode. The CI workflow covers Linux x86_64, macOS aarch64, and Windows x86_64 with Bazel 9.3.0, the minimum supported version. The remaining catalog architectures are not covered by that workflow.

JDK archives are fetched on demand for selected toolchains; adding the module does not require downloading every platform's JDK. The configured repository cache can reuse archives across workspaces.

See the API reference, contributor guide, and release procedure.

Maintenance and support

David Ostrovsky (@davido) maintains this project on a best-effort volunteer basis and is the point of contact for the Rules Authors SIG. The goal is to respond to issues and pull requests within 2–3 weeks; there is no guaranteed response time or commercial support. Additional maintainers are welcome.

The catalog follows non-LTS JDK releases, whose vendor maintenance windows are short. A catalog entry does not extend the vendor's security support. Retiring public labels follows the versioning policy in RELEASING.md.

Adding the next non-LTS release

1. Add the archive structs to jdk/repositories.bzl (name, target_compatible_with, sha256, strip_prefix, urls, version), mirroring the JDK 27 entries.
2. Add a remote_jdkNN_repos() macro and call it from jdk/extensions.bzl.
3. List the new repos in MODULE.bazel (use_repo + register_toolchains).
4. Add the remotejdk_NN alias and toolchain_jdk_NN to toolchains/BUILD.bazel.
5. Document the vendor's support window and announce any eventual removal as described in RELEASING.md.

License

Apache License 2.0. See LICENSE.