Use 'Toolchains for JVM projects' of Gradle 6.7+

Gradle 6.7 introduced ‘Toolchains for JVM projects’.

Reference: https://docs.gradle.org/6.8.2/userguide/toolchains.html

So my suggestion is changing sourceCompatibility to:

java {
    toolchain {
        languageVersion = JavaLanguageVersion.of(generation)
    }
}

https://github.com/spring-io/initializr/blob/835f69986cf7c09246ebdfd33478a70c411910de/initializr-generator/src/main/java/io/spring/initializr/generator/buildsystem/gradle/GroovyDslGradleBuildWriter.java#L89-L92

https://github.com/spring-io/initializr/blob/8cef356bcf1f28033077f767bc78cab36fd10d89/initializr-generator/src/main/java/io/spring/initializr/generator/buildsystem/gradle/KotlinDslGradleBuildWriter.java#L83-L86

[wilkinsona]

Thanks for the suggestion, but I don’t think we should do this. Using Gradle’s Toolchain support may result in it attempting to download a JDK to meet the project’s needs. That’s something that may not always be desirable and in some organisations it wouldn’t be permitted. I think it’s better if we leave it as an opt-in.

Let’s see what the rest of the team thinks.

[snicoll]

As Andy mentioned, we really need to add what is strictly necessary out-of-the-box and let users complete their build with additional options if necessary. Thanks for the suggestion, in any case.