(ns myorg.plugin.orc-output
  (:import
   [myorg.helpers.fs-input-stream FsInputStream]
   [ URL]
   [ File]
   [java.nio.file Path]
   org.apache.hadoop.conf.Configuration
   [org.apache.orc OrcFile]
   [org.apache.hadoop.fs FileSystem FileSystem$Statistics FSDataInputStream FSDataOutputStream]))

(set! *warn-on-reflection* true)

(defn to-path
  [x]
  {:post (instance? Path %)}
  (cond
    (instance? URL x) (Path. (.toURI ^URL x))
    (instance? File x) (Path. (.getPath ^File x))
    (string? x)                (Path. ^String x)
    (instance? Path x)         x))

(def dummy-path (to-path "dummy"))

(def orc-header-length (count OrcFile/MAGIC))

(defn input-stream-filesystem [buffered-bytes]
  (proxy [FileSystem] []
    (open [_]
      (FSDataInputStream. (FsInputStream. buffered-bytes)))))

(defn create-orc-reader [buffered-bytes]
  (OrcFile/createReader dummy-path (doto (OrcFile/readerOptions (Configuration.))
                                     (.maxLength (count buffered-bytes))
                                     (.filesystem (input-stream-filesystem buffered-bytes)))))

Then I've test for namespace myorg.plugin.orc-output called myorg.plugin.orc-output-test. It has very basic test

(ns myorg.plugin.orc-output-test
  (:require [clojure.test :refer :all])
  (:require [myorg.plugin.orc-output :refer :all]))

(deftest orc-create
  (is (= 1 1)))

When I run the test I get error

Syntax error (ClassNotFoundException) compiling at (myorg/plugin/orc_output.clj:1:1). myorg.helpers.fs-input-stream.FsInputStream Full report at: /var/folders/b_/_t677thx43n6pd8l8x0c1qjr0000gp/T/clojure-13616919898936783952.edn

The project is in https://github.com/rajcspsg/gen-class-error-demo as well.

How can I fix this?

You are not aot compiling the namespace with the gen-class in it

You also are not requiring the namespace that defines the class from the namespace that uses it

You also are not using the correct name for the class, you need to replace all - with _

The docstring for gen-class helpfully tells you it does nothing when "not compiling", but unhelpfully clojure is always compiled to bytecode, so in this case "compiling" means aot compiling

but I'm stuck more on this

how can I aot compile this in deps.edn?

do I have to add (require 'myorg.plugins.helper.FsInputStream) ?

no

in general aot compilation is a separate step your build tool is usually responsible for

clj and deps.edn are not really a complete build tool, but they work together with tools.build (https://clojure.org/guides/tools_build) #C02B5GHQWP4

aot (a head of time) compilation in clojure means generating jvm bytecode classfiles and writing them to disk, instead of just keeping it in memory (what the clojure compiler normally does with bytecode)

if you are new to clojure, gen-class is pretty terrible to work with, in general if you can it is much better to use reify/deftype/defrecord then proxy, then if you must gen-class (a lot of people would prefer to write some stub java than use gen-class)

ohh okay

Thanks hiredman