GitHub - bazel-starters/java: Template for developing Java apps with Bazel

Java Bazel Starter

# This is executable Markdown that's tested on CI.
# How is that possible? See https://gist.github.com/bwoods/1c25cb7723a06a076c2152a2781d4d49
set -o errexit -o nounset -o xtrace
alias ~~~=":<<'~~~sh'";:<<'~~~sh'

This repo includes:

🧱 Latest version of Bazel and dependencies
📦 Curated bazelrc flags via [bazelrc-preset.bzl]
🧰 Developer environment setup with [bazel_env.bzl]
🎨 google-java-format and pmd/checkstyle, using rules_lint
✅ Pre-commit hooks for automatic linting and formatting
📚 Maven package manager integration

Note

You can customize languages and features with the interactive wizard in the aspect init command. init is an alternative to this starter repo, which was generated using the 'java' preset. See https://docs.aspect.build/cli/overview

Setup dev environment

First, we recommend you setup a Bazel-based developer environment with direnv.

install https://direnv.net/docs/installation.html
run direnv allow and follow the prompts to bazel run //tools:bazel_env

This isn't strictly required, but the commands which follow assume that needed tools are on the PATH, so skipping direnv means you're responsible for installing them yourself.

Try it out

Create a minimal Java application:

mkdir src
>src/Demo.java cat <<EOF
class Demo {
    public static void main(String[] args) {
        System.out.println("Hello from Java");
    }
}
EOF

We didn't wire up the BUILD file generator for Java yet, so users are forced to write this manually.

touch src/BUILD
buildozer 'new_load @rules_java//java:java_binary.bzl java_binary' src:__pkg__
buildozer 'new java_binary Demo' src:__pkg__
buildozer 'add srcs Demo.java' src:Demo

Now the application should run, and we can verify it produced the expected output:

output="$(bazel run src:Demo)"

[ "${output}" = "Hello from Java" ] || {
    echo >&2 "Wanted output 'Hello from Java' but got '${output}'"
    exit 1
}

Linting

Run aspect lint, a task in Aspect CLI. This is configured to run PMD by default, though you could run other tools.


INFO: Build completed successfully, 3 total actions
Lint results for //src:Demo:
Summary:

warnings: 0

Using protobuf and gRPC

Let's introduce a small data schema.

>src/foo.proto cat <<EOF
syntax = "proto3";
option java_package = "build.aspect.examples";
option java_outer_classname = "FooOuterClass";
message Foo {
    string message = 1;
}
EOF

Generate the BUILD rules for protobuf:

There isn't a Gazelle generator for java_proto_library yet, so add it manually:

buildozer 'new_load @protobuf//bazel:java_proto_library.bzl java_proto_library' src:__pkg__
buildozer 'new java_proto_library foo_java_proto' src:__pkg__
buildozer 'add deps :foo_proto' src:foo_java_proto
buildozer 'add deps :foo_java_proto' src:Demo

Now overwrite Demo.java to use the generated Foo message:

>src/Demo.java cat <<EOF
import build.aspect.examples.FooOuterClass;
class Demo {
    public static void main(String[] args) {
        FooOuterClass.Foo foo = FooOuterClass.Foo.newBuilder()
            .setMessage("Hello from Java Protobuf!")
            .build();
        System.out.println(foo);
    }
}
EOF

Run the application again:

output="$(bazel run src:Demo)"

[ "${output}" = "message: \"Hello from Java Protobuf!\"" ] || {
    echo >&2 "Wanted output 'Hello from Java Protobuf' but got '${output}'"
    exit 1
}