def create_jar_builder(self, jar):
    """Creates a ``JarTask.JarBuilder`` ready for use.

    This method should be called during in `execute` context and only after ensuring
    `JarTask.JarBuilder.prepare` has already been called in `prepare` context.

    :param jar: An opened ``pants.backend.jvm.tasks.jar_task.Jar`.
    """
    builder = self.JarBuilder(self.context, jar)
    yield builder
    builder.commit_manifest(jar)
Creates a ``JarTask.JarBuilder`` ready for use.

    This method should be called during in `execute` context and only after ensuring
    `JarTask.JarBuilder.prepare` has already been called in `prepare` context.

    :param jar: An opened ``pants.backend.jvm.tasks.jar_task.Jar`.