Springboot application fails to start with default configuration from version >= 2.5

Is there an existing issue for this?

[X] I have searched the existing issues

Describe the bug

With the release of spring 2.5, if one uses it along with gradle, by default it will generate a library next to your executable jar, when you run the ./gradlew build command. The default start command generated by the JavaProvider in nixpacks is java $JAVA_OPTS -jar -Dserver.port=$PORT build/libs/*.jar. If there are multiple *.jar files in the build/libs folder it can point to the one which is not an executable, in this case the *plain.jar.

When you run the image you'll get the following error:

no main manifest attribute

This is because it tries to execute a jar, which is in reality a library.

Of course the user can modify the gradle.build configuration, to not generate the *plain.jar, however to provide a better user experience that works without requiring user intervention would be a good thing. (Mentioned here: https://github.com/railwayapp/nixpacks/issues/677)

Solution:

From spring v2, there is a dedicated gradle task, called bootJar that only generates an executable jar file. If one modifies the JavaProvider to do this, for gradle + spring applications the problem goes away. However, this means that spring v1 applications won't work anymore.

I can provide a PR, along with the modifications to implement this.

My question is, is it okay to drop the support of spring v1 applications? The last release was back in 2007. I am not sure how many users of nixpacks use spring v1, so that would be an interesting metric also to decide this.

To reproduce

Steps to reproduce the bug:

Clone an example spring v3 project, for eg.: https://github.com/appuio/example-spring-boot-helloworld
Run nixpacks build . in the project root
Use docker to run the image
Results in an error: no main manifest attribute, in build/libs/app-0.1.1-SNAPSHOT-plain.jar

Expected behavior

The expected behaviour would be that a default spring >= v2.5 project works out of the box without the need to overwrite default configurations.

Environment

OS version: macOS 13.5.2
nixpacks version: 1.16.0

railwayapp / nixpacks