Hello! I'm working in a monorepo and trying to uberjar our projects using tools.build . I've gotten the uberjar compiling and built, but running it with java -jar , I keep hitting a java.lang.ClassNotFoundException. Could not find or load main class monorepo.base.core . I'm defining my main namespace in build.clj and passing it to :main in the uber fn, the pom.xml thats generated seems to be correct, and all the classes and files are present and correctly structured in target/classes as needed for it to compile. Unpacking the jar after its built I've confirmed the -main namespace is present, but still it cant be found despite my best efforts. Is there something obvious I'm missing here? My only guess is creating a source pom.xml that defines a main, to pass into write-pom , as I dont see Main-Class in the generated pom. But the attribute is obviously being set somewhere with the uber fn when it builds. Here is my build.clj, pretty much straight from the tools.build guide.

(ns build
    (:require [clojure.tools.build.api :as b]))

(def lib 'monorepo/project)
(def main 'monorepo.base.namespace_with_mainfn)
(def version (format "1.2.%s" (b/git-count-revs nil)))
(def class-dir "target/classes")
(def basis (b/create-basis {:project "deps.edn"}))
(def uber-file (format "target/%s-%s-standalone.jar" (name lib) version))


(defn clean [_]
      (b/delete {:path "target"}))

(defn prep [_]
      (b/write-pom {:class-dir class-dir
                    :lib lib
                    :version version
                    :basis basis
                    :src-dirs ["src"]})
      (b/copy-dir {:src-dirs ["../../bases/base" "."]
                   :target-dir class-dir}))

(defn uber [_]
      (b/compile-clj {:basis basis
                      :src-dirs ["src" "resources"]
                      :class-dir class-dir})
      (b/uber {:class-dir class-dir
               :main main
               :uber-file uber-file
               :basis basis}))

the class not found is monorepo.base.core - your main namespace is monorepo.base.namespace_with_mainfn so those do not seem directly related

just going from the error, do you see monorepo.base.core in your uberjar?

re "I dont see `Main-Class` in the generated pom" - do you mean in the META-INF/MANIFEST.MF ?

the pom is not used by Java to do anything, so is irrelevant here

Apologies I mistyped, the error message is indeed with the defined monorepo.base.namespace_with_mainfn . I do see monorepo.base.namespace_with_mainfn in my uberjar after its built

a .class?

that is, the uberjar should have monorepo/base/namespace_with_mainfn.class in it

yes, its inside the jar as a .class file

and inside META-INF/MANIFEST.MF ?

I dont have a MANIFEST.MF under my META-INF. contents is: META-INF/maven/monorepo/project/pom.xml and pom.properties

well something doesn't match up here. uber should always write a META-INF/MANIFEST.MF into the uber jar, and I don't know how it would be finding that class name otherwise

you won't see this in the target/classes dir, only in the uberjar

jar tf target/project-V-standalone.jar META-INF/MANIFEST.MF should verify it exists

(whatever V you have)

oh sorry, yes inside the uberjar I have MANIFEST.MF and Main-Class is defined there correctly as monorepo.base.namespace_with_mainfn

well, then I don't understand the error. what's the exact command you're running?

just java -jar target/project-standalone.jar

after running clj -T:build clean/prep/uber

can you dump the full output?

from the java command?

Its just this short one

Error: Could not find or load main class monorepo.base.namespace_with_mainfn
Caused by: java.lang.ClassNotFoundException: monorepo.base.namespace_with_mainfn

and you see jar tf target/project-standalone.jar monorepo/base/namespace_with_mainfn.class ?

waiting for it to uber again to see if this was the issue! It is there, but its under /classes/monorepo/base/namespace_with_mainfn.class , added classes in front of my main def in build.clj 🤞

Thinking I incorrectly assumed :class-dir was ignoring/handling that. will update when it finishes

oh, well that's definitely not the right place, but that doesn't sound like the right fix

I don't understand how you're getting that from the script above

you should maybe clean target if you haven't been doing that, too

ahhh, yes finally finished

Error: Could not find or load main class classes.monorepo.project.namespace_with_mainfn
Caused by: java.lang.NoClassDefFoundError: monorepo/project/namespace_with_mainfn (wrong name: classes/monorepo/project/namespace_with_mainfn)

have been cleaning target each time. full clean/prep/uber

the wrong path is being included in the uber jar, but I don't understand how you're getting that with the script above.

(def main 'monorepo.base.namespace_with_mainfn) is just wrong

main is just the namespace with the main defn

no path stuff, no extra bits at the front

hard for me to tell whether that is correct or not without knowing what the namespaces are

that is just the namespace, as its shown at the top of the file with my -main function.

yeah, so I don't think that is the wrong part

the wrong part is that you are getting a classes/ prefix dir included but I can't tell whether this class is coming from some other part of the monorepo via a local dep or from this part as you have not provided enough information

What's in ../../bases/base? What's in .? What's in target/classes after the copy? after the compile?

the write-pom is not needed and can be removed

what's in your deps.edn? are you using local/root deps?

This is a polylith monorepo, so the top level folder structure is

▾ workspace
  ▸ bases
  ▸ components
  ▸ development
  ▸ projects

after compile it looks the same. and the uberjar is built as expected under thisProject/target

why does classes contain a classes dir?

ah, word wrapped, node_modules/classes

that does seem suspicious, it doesn't seem like node_modules should have a classes subdir, but I don't know enough about node and can't see how that would end up effecting the uberjar

oh

no they actually are two separate ones. target/classes is where everything in the copy-dir is going, and shouldnt affect much. thisProject has a /classes folder that contains all the dependencies from deps.edn, so when I copy-dir "." , which is my thisProject dir, it copies over /classes as well into target/classes

what are the paths in your deps.edn? I bet your basis, is pointing to stuff up the directory tree, in conflict with the result of the copying everything into .

your deps.edn presumably has like a local dep on ../bases/subproject

(in which case I am not sure what the copy is for)