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Working across Bazel and Maven

Some users may need to work across Bazel and Maven projects. Particularly there are two common use cases.

Use SNAPSHOT jars produced by Maven in a Bazel project

To use SNAPSHOT jars in a Bazel project just like one would in Maven, the following steps need to be taken.

The process for using SNAPSHOT jars produced by Maven

  1. Copy or link SNAPSHOT jar to same directory as or relative to Bazel BUILD file.
  2. Create a java_import rule that points to the SNAPSHOT jar.
  3. Replace maven_install rule in dependency list with java_import.
  4. Build and profit.

Example

Copy the SNAPSHOT jar.

cd $BUILD_DIR
cp ~/.m2/repository/org/slf4j/slf4j-api/1.7.29/slf4j-api-1.7.30-SNAPSHOT.jar .

Or symlink to it. The advantage of using a link is that the jar can be updated by Maven and re-run build in Bazel.

cd $BUILD_DIR
ln -s ~/.m2/repository/org/slf4j/slf4j-api/1.7.29/slf4j-api-1.7.30-SNAPSHOT.jar .

Create java_import rule in BUILD file. In this example, we'll use slf4j-api. This assumes that the location of the SNAPSHOT has been copied or symlinked to the same directory as the BUILD file.

java_import(
    name = "org_slf4j_slf4j_api",
    jars = [":slf4j-api-1.7.30-SNAPSHOT.jar"],
)

Then, in the deps attribute replace maven_install rule for slf4j-api with the java_import that was just created.

java_library(
    name = "fruit-api",
    srcs = glob(["src/main/java/**/*.java"]),
    visibility = ["//visibility:public"],
    deps = [
      ...
      ":org_slf4j_slf4j_api", # instead of "@maven//:org_slf4j_slf4j_api"
      ...
    ],
)

Build SNAPSHOT jars with Bazel and use them in a Maven project

Similar to above, we can generate SNAPSHOT jars using Bazel, so that they can be used in Maven projects. See below for detailed steps.

The process for generating SNAPSHOT jars using Bazel

  1. Make code changes to the library which you want to release SNAPSHOT jar for.
  2. Build your library by running bazel build <path to the library>.
  3. Run bazel run @pomgen//:update -- --package <path to the library> to update version of your library artifact.
  4. Run bazel run @pomgen//maven -- -a pomgen to generate poms
  5. Run bazel run @pomgen//maven -- -a install to install the libraries into ~/.m2/repository.
  6. Update the pom.xml in the consuming Maven project to use -SNAPSHOT of your library.

Example

Make some code changes in examples/hello-world/healthyfoods/fruit-api.

Run bazel build.

bazel build //examples/hello-world/healthyfoods/fruit-api

Update artifact version.

bazel run @pomgen//:update -- --package examples/hello-world/healthyfoods/fruit-api

Generate pom(s).

bazel run @pomgen//maven -- -a pomgen

Install the built library into ~/.m2/repository.

bazel run @pomgen//maven -- -a install

Then, update the pom.xml of the consuming Maven project.

<dependency>
    <groupId>com.pomgen.example</groupId>
    <artifactId>fruit-api</artifactId>
    <version>1.0.0-SNAPSHOT</version>
</dependency>

Now you can compile your Maven project, it should be using the latest SNAPSHOT jars produced by Bazel.