Override the Maven property java.version for projects using spring-boot-starter-parent

[timtebeek]

As you're probably well aware, Maven projects using spring-boot-starter-parent can override the java.version property to set the maven.compiler.source and maven.compiler.targer versions. These are defined in the parent pom.xml through their build.gradle file.

It would make sense (to me at least) to define this property when needed, and override the value for such Spring Boot projects when moving from Java 8 to 11. That way users have one less manual step to perform when migrating in bulk from 8 to 11.

I imagine the implementation would not need much Spring specifics:

• you'll want to find spring-boot-starter-parent, anywhere up the hierarchy,
• detect the presence of the property value, also up the hierarchy,
• if the nearest value is below 11, define the property with the new value.

[timtebeek]

A naive approach wouldn't even need to know about the spring-boot-starter-parent and can just override the java.version property through org.openrewrite.maven.ChangePropertyValue, not adding it if not present already.

[tkvangorder]

@timtebeek , thanks for the suggestion. We initially decided against setting this property because those risk-averse enterprises might choose to first upgrade their dependencies (in preparation for the move to 11) but still want to continue to compile with Java 8.

I think now with the Java releases coming fast and furious, it would be a good time to do this by default (and it helps that we now have a maven model that would allow us to do this accurately)

[tkvangorder]

We might need to write an imperative recipe for this, so we can walk up the parent hierarchy and place the property (if it does not exist) at the root project.

[timtebeek]

This was briefly discussed over Slack; here's a naive approach that merely bumps the property version if it's already defined: main...timtebeek:SpringBootJavaVersion11 Could be an intermediate step while we wait for an imperative recipe. Unlikely to hurt if the property is already there.