Spring Boot Gradle app on Heroku: Unable to access jarfile

I eventually found a very helpful thread here: Running Spring app built with gradle on Heroku

Which helped me with my problem - this thread seems to be more detail than Heroku's official guide.

You must add the following code to your build.gradle file:

task stage(type: Copy, dependsOn: [clean, build]) {    from jar.archivePath    into project.rootDir    rename {        'app.jar'    }}stage.mustRunAfter(clean)clean << {    project.file('app.jar').delete()}

Then, point your Procfile to the app.jar:

web: java $JAVA_OPTS -jar app.jar

You don't need to modify your stage task for that.

In your gradle.build file, make sure to give a name to your built artifact like this.

jar {    baseName = 'app'    version = '0.0.1'}

With that been done, and the following in Procfile, it should just run fine.

web: java -Dserver.port=$PORT $JAVA_OPTS -jar build/libs/app-0.0.1.jar

I found that if name is not explicitly defined, heroku seems to name the artifact something like build-{buildNumber}.jar and no wonder it will never find the app.jar.

Also, if not set already, the build pack needs to be set.

heroku config:set GRADLE_TASK="build"

According to the documentation:

The Gradle buildpack will automatically detect the use of the Spring Boot and Ratpack web frameworks.

The web command should be overridden only if needed. If you're using Spring Boot, you shouldn't need to specify a Procfile at all.

Delete it, and get your app running without further configuration.