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2023-11-04

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#tools-build
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2023-11-04
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practicalli-johnny17:11:58

tools.build uber function seems to create a multi-release uberjar by default, so I am trying to understand the benefits with respect to deploying a Clojure service as an uberjar. Are these correct reasons for using multi-release uberjar and are there further reasons to use a multi-release uberjar 1. run a Clojure service on a different version of the JVM than it was built upon (avoiding the need to create an uberjar for each release of Java that might be on the server environment) ? 2. use classes or jar files compiled elsewhere, potentially compiled with a different version of the JDK (i.e. library dependencies from Clojars / Maven) ? I assume 1. is not significant when there is control over the JVM being used to run the service, e.g. in a containerised build and deploy. I also assume a multi-release is more significant as the amount of Java interop is used in the service or library dependencies. Thank you.

practicalli-johnny17:11:57

I can tell uber to set the uberjar manifest to switch off the multi-release if there is a value to doing this 

(build-api/uber {:basis     project-basis
                     :class-dir class-directory
                     :main      main-namespace
                     :manifest {"Multi-Release" "false"}
                     :uber-file uberjar-file})
I only noticed the uberjar was a multi-release as jdeps command complained that I didn't pass a --multi-release <jdk-version> argument 🙂

hiredman17:11:33

It is very likely incidental

hiredman17:11:33

Like Uber doesn't make a multi release jar, but one of your dependencies is multi release and Uber is merging the keys in the manifests or something

hiredman17:11:54

Not sure though

Alex Miller (Clojure team)18:11:23

The purpose of MR jars is to allow you to have JDK-specific classes in your jar, so you can lord different versions depending on available jdk stuff

Alex Miller (Clojure team)18:11:56

Uber is just exploding and merging so one of your source jars is likely mr

practicalli-johnny09:11:27

Ah, so a multi-release uberjar is created when one of the libraries used in the project is a multi-release jar. So any dependency jar that has "Multi-Release" "true" in it's manifest sets that for the generated uberjar. Now I am curious as to which jars are setting this, but it's probably not that valuable to know unless I experience an issue. That all makes sense. Thanks