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Generate external dependencies from Maven projects

The tool generate_workspace helps automate the process of writing the WORKSPACE file for a Java project. This tool is helpful when the list of external dependencies is long, such as when working with external transitive dependencies.

The generate_workspace tool will generate a generate_workspace.bzl file which includes:

  • the generated_maven_jars macro that will contain the transitive dependencies, and
  • the generated_java_libraries macro that will contain a library for each maven_jar.

Install generate_workspace

Bazel's binary installer does not include generate_workspace. To be able to use this tool:

  1. Clone Bazel's migration tooling repo:

    git clone https://github.com/bazelbuild/migration-tooling.git
    
  2. Run the following to build the generate_workspace tool and see usage:

    bazel run //generate_workspace
    

Generate a list of external dependencies

  1. Run the generate_workspace tool.

    When you run the tool, you can specify Maven projects (that is, directories containing a pom.xml file), or Maven artifact coordinates directly. For example:

    $ bazel run //generate_workspace -- \
    >    --maven_project=/path/to/my/project \
    >    --artifact=groupId:artifactId:version \
    >    --artifact=groupId:artifactId:version
    Wrote
    /usr/local/.../generate_workspace.runfiles/__main__/generate_workspace.bzl
    

    The tool creates one outputs, a generate_workspace.bzl file that contains two macros:

    1. The generated_maven_jars macro that will contain the transitive dependencies of the given projects and artifacts.
    2. The generated_java_libraries macro will contain a library for each maven_jar.

    If you specify multiple Maven projects or artifacts, they will all be combined into one generate_workspace.bzl file. For example, if an artifact depends on junit and the Maven project also depends on junit, then junit will only appear once as a dependency in the output.

  2. Copy the generate_workspace.bzl file to your workspace. The .bzl file's original location is listed in the commandline output.

    To access external dependencies:

    1. Add the following to your WORKSPACE file:

      load("//:generate_workspace.bzl", "generated_maven_jars")
      generated_maven_jars()
      

      You can now access any of the jars in generate_workspace.bzl.

      This reference points to the jar, but not to any dependencies that the jar itself may have. To have a target depend on one of these jars, you must list the jar as well as each of that jar's dependencies.

      For example, to depend on the Guava jar from the Guava project, in the target definition you will need to list the jar and its transitive dependencies:

      deps = [
        "@com_google_guava_guava//jar",
        "@com_google_code_findbugs_jsr305//jar",
        "@com_google_errorprone_error_prone_annotations//jar",
        "@com_google_j2objc_j2objc_annotations//jar",
      ]
      
    2. Optionally, you can also access the libraries. When you list a library as a dependency, the transitive dependencies are already included, and so you don't need to list them manually.

      To access the libraries, add the following to a BUILD file:

      load("//:generate_workspace.bzl", "generated_java_libraries")
      generated_java_libraries()
      

      The recommended location for this BUILD file is in a directory called third_party.

      You can now access any of the Java library targets in generate_workspace.bzl.

      For example, for a target to depend on Guava and its transitive dependencies, in the target definition you will need to list:

      deps = ["//third_party:com_google_guava_guava"]
      
  3. Ensure generate_workspace.bzl lists the correct version of each dependency.

    If several different versions of an artifact are requested (for example, by different libraries that depend on it), then generate_workspace chooses a version and annotates the maven_jar with the other versions requested.

    Here's an example of the contents of generate_workspace.bzl:

    # org.springframework:spring:2.5.6
    # javax.mail:mail:1.4
    # httpunit:httpunit:1.6 wanted version 1.0.2
    # org.springframework:spring-support:2.0.2 wanted version 1.0.2
    # org.slf4j:nlog4j:1.2.24 wanted version 1.0.2
    native.maven_jar(
        name = "javax_activation_activation",
        artifact = "javax.activation:activation:1.1",
    )
    

    The example above indicates that org.springframework:spring:2.5.6, javax.mail:mail:1.4, httpunit:httpunit:1.6, org.springframework:spring-support:2.0.2, and org.slf4j:nlog4j:1.2.24 all depend on javax.activation. However, two of these libraries wanted version 1.1 and three of them wanted 1.0.2. The WORKSPACE file is using version 1.1, but that might not be the right version to use.