How to use the java-buildpack together with the apt-buildpack?

Question

What I am trying to accomplish
I'm trying to get a Spring Boot application running on Cloud Foundry, which also need some things that need to be installed with apt.

To install said things, I'm using the apt-buildpack.

What works
When I push just the JAR for the application everything works as expected:

cf push my-spring-boot-app -f manifest.yml -p my-spring-boot-app.jar

The app then gets successfully built and deployed.

What doesn't work
When I add the apt-buildpack to the manifest, the apt-buildpack is then successfully executed but the java-buildpack doesn't seem to find my jar. It throws the following error:

ERROR Compile failed with exception #<RuntimeError: No container can run this application. Please ensure that you’ve pushed a valid JVM artifact or artifacts using the -p command line argument or path manifest entry. Information about valid JVM artifacts can be found at https://github.com/cloudfoundry/java-buildpack#additional-documentation. >
No container can run this application. Please ensure that you’ve pushed a valid JVM artifact or artifacts using the -p command line argument or path manifest entry. Information about valid JVM artifacts can be found at https://github.com/cloudfoundry/java-buildpack#additional-documentation. 
Failed to compile droplet

My manifest.yml (which defines the buildpacks and the artifact(s) to upload) looks something like this:

caasp_version: 4
applications:
  - name: my-spring-boot-app
    path: ./target/app #Directory which includes the apt.yml and my-spring-boot-app.jar
    instances: 1
    memory: 2GB
    disk_quota: 2GB
    stack: cflinuxfs3
    buildpacks:
      - apt_buildpack
      - java_buildpack

What I've already tried

• I've already confirmed that the JAR, aswell as the apt.yml, are indeed uploaded into the container.
• Renamed my JAR to aaa.jar to ensure it is placed before the apt.yml file.
• Enabled debugging for the java_buildpack, which I did not help me.

My question
How can I build/deploy my Spring Boot application while also using the apt-buildpack?

Thanks in advance for any answers :)

Answer 1

After some consultation with the maintainers of the java-buildpack, I've found a solution.

The problem is that the java-buildpack expects either a JAR or a folder with the contents of the exploded JAR. That means supplying a folder with the apt.yml and the JAR won't work.

I've solved this with a simple bash script that moves the apt.yml and JAR into a folder and then explodes the jar. This folder can then be pushed with cf push.

The bash script looks like this(fast and ugly):

rm -rf "$1/target/app"
mkdir "$1/target/app"
cp $1/apt.yml $1/target/app/apt.yml
cp $1/target/my-spring-boot-app.jar $1/target/app/my-spring-boot-app.jar

cd $1/target/app
jar xfmy-spring-boot-app.jar

and gets called by a Maven plugin after the build process:

    <build>
        <plugins>
            <plugin>
                <artifactId>exec-maven-plugin</artifactId>
                <groupId>org.codehaus.mojo</groupId>
                <version>3.1.0</version>
                <executions>
                    <execution>
                        <id>Create /app directory</id>
                        <phase>package</phase>
                        <goals>
                            <goal>exec</goal>
                        </goals>
                        <configuration>
                            <executable>/bin/bash</executable>
                            <arguments>
                                <argument>${basedir}/scripts/create-app-directory.sh</argument>
                                <argument>${basedir}</argument>
                            </arguments>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>