Configure Gradle's toolchain when Gradle does not handle the requested Java version

Steps to reproduce

• Select the following properties on https://start.spring.io/:
  • Project: Gradle Project
  • Language: Java
  • Spring Boot: 2.4.5
  • Java: 16
• Generate project

Behavior

When I try to build the project with ./gradlew assemble Java 16, it fails:

> startup failed:
  General error during semantic analysis: Unsupported class file major version 60
  
  java.lang.IllegalArgumentException: Unsupported class file major version 60

It seems that the generated project contains a build.gradle file with sourceCompatibility = '11'. Also, the project has Gradle version 6.8.3 which does not support Java 16 out of the box and the project does not use Gradle toolchain.

[vpavic]

The way I see it:

• Gradle wrapper
  • if you don’t use it you might end up using the wrong Gradle version which could fail
  • if you use it, it will download the needed Gradle version only once
• Gradle toolchains
  • if you don’t use it you might end up using the wrong JDK version which could fail
  • if you use it, it will either pick it up from the supported locations or download the needed JDK only once

That looks fairly analogous to me. And a far better developer experience OOTB, at least IMO.

Once a project’s being configured to use a toolchain, I don’t think it’s possible to avoid using it without changing the build script.

I’ve been using toolchains for quite some time now and in practice it has never downloaded a JDK for me, because it will pick up the appropriate JDK from my local SDKMAN installation.

Additionally, you might also take into consideration that for some time now Gradle promotes toolchains as the way of declaring Java version (see the very first snippet from the Building Java & JVM projects page of the user manual) and that sourceCompatibility and targetCompatibility are referred to as historical options for the Java compiler.

[vpavic]

From today’s standpoint, would you be open to configure Gradle’s toolchain by default, as originally proposed in #1187?

There are numerous benefits of using Gradle toolchain on top of the case expressed in this issue. A project that configures toolchain is ensured to always build using the appropriate Java version. With the ecosystem becoming increasingly split between 3 different Java version (8, 11 & 17) this feature just becomes more attractive.

it can cause Gradle to download a JDK which may be blocked or prohibited for some users

Isn’t this basically the same as with the Gradle wrapper itself? You still use the wrapper in generated projects even though some environments might be more prohibitive about it and prefer to use their own Gradle distribution. Personally I wouldn’t conflate such considerations with initializr.