[PROPOSAL] Allow Gradle to run without a JDK installed

[blindpirate]

@bmuschko @oehme As we discussed several days ago, for developers who use non-JVM languages, it might be an obstacle to have a JDK installed in their machines. So here I propose a feature for Gradle: a brand-new wrapper mechanism, which supports running Gradle in docker completely.

For example, there's a script named gradlewd, when an user runs ./gradlewd <tasks>, it will make sure gradle docker image with specific version exists, and then run build in it. Obviously, it has some advantages:

• Users dont' need to preinstall JDK.
• Bootstrap jar (gradle-wrapper.jar) may be not necessary any more.
• Build environment is isolated and reproducible totally, this seems to be a tendency.
• to be continued...

However, it has disadvantages:

• Docker images is much larger than jar distributions.
• Can we still have gradle deamon as usual?
• to be continued...

I have created a simple demo project https://github.com/blindpirate/gradlewd-demo and I'd like to hear your opinions.

[oehme]

Hey Bo,

this is definitely an interesting way to get rid of the JDK requirement. On the other hand, it adds a big new requirement - Docker. And as you noted correctly, Docker images are quite large to download.

We have thought about this in the past as well and arrived at a somewhat different solution, consisting of two parts:

1. A gradlew executable that does not need Java
2. Gradle distributions that come with a bundled JDK

How does that approach sound to you?

[blindpirate]

Happy to know that you've already discussed it and reached a consensus. However, I think in some cases, this mechanism is worthwhile, especially when user already have docker installed. So please allow me to keep this proposal open in case some day the team want to make some change.

Since docker image is layer-structured, the size issue might not be very striking (I should try to do some investigation). Thanks for your response, @oehme !

[oehme]

I'm not saying we reached consensus (we haven't made any decision yet), I was just interested what you think about the embedded JDK approach.

If you don't mind I'd like to change this ticket to a more general name, like "Allow Gradle to run without a JDK installed". Which way we do it is more of an implementation detail. We should eventually agree on one solution though, because multiple different ones would be more confusing than helpful I think.

[blindpirate]

Well, embedded JDK is sure a solution, but it seems that the solution cost much more work than docker, especially for multi-platform (that means writing install or bootstrap script for all platforms). Actually, in my view, using docker is not only to avoid preinstalled JDK, but also to ensure the isolation and reproducibility of build. For example, docker and kubernetes are using docker in build, so I think it could be an option.

Thank you for your advice, I have changed this ticket title. Please give me some time and let me do some research to see pros and cons in detail.

[bmuschko]

You might find this spec interesting. It defines the concept of a build platform. As part of the platform you can declare a Java version. This concept might be extended to download a JDK as part of the platform. The document only gathers some thoughts. We haven't agreed upon the functionality nor did we start implementing any of the stories.

[oehme]

@bmuschko I don't think this spec fits the bill. It is an elaborate DSL in settings.gradle, so you couldn't parse that without already having started Gradle. What we need for this story is something that works with minimal bootstrapping.

[bmuschko]

@oehme Ah, I must have misread the first description. Yeah, that wouldn't help then.

[apahne]

I'd favour "A gradlew executable that does not need Java". That's doable using the Java 9 module system, isn't it? The executable(s) would be OS specific, right?

[nlwillia]

With Java moving to a 6-month release train model, it will be increasingly difficult to assume that the local environment has an up-to-date JDK containing all the features that a Gradle build might want to use.

Oracle has said that they won't be pushing every new version through the Java client update process, and that developers should consider embedding their own copy.

Oracle does not plan to migrate desktops from Java 8 to later versions via the auto update feature. Individuals who require Java SE for non-corporate desktop use will continue to receive updates through at least December 2020. Instead of relying on a pre-installed standalone JRE, we encourage application developers to deliver JREs with their applications.

While that's talking specifically about JREs, JDKs are going to face similar issues, and the idea that Gradle could fully bootstrap itself if necessary is appealing.

[gmcouto]

Or we should create an open-source script called something like jdkw that downloads java, add to current session's path and set JAVA_HOME when used... gradle could use something like that.
Actually, many projects could use it, not only gradle, and by that we can ensure it's reliability.

I'd love to be able to just have a few wrapper scripts and have the whole build environment ready with just one command in a brand-new machine.

Something like this, but multiplatform like gradlew is for gradle:
https://github.com/vjkoskela/jdk-wrapper