build.boot

;; As of September 2016, using the version of boot-clj that I got by following the Nix install instructions,
;; here is how I built a clojure "hello world" as a uberjar that you can run with `java -jar`.  I do 
;; not claim it is the right way, merely that it worked for me.  This file is build.boot

(set-env!
 :resource-paths #{"src"}  ; may be optional?
 :source-paths #{"src"}    ; my code is in src/myapp/core.clj
 :dependencies '[[org.clojure/clojure "1.8.0"]]) ; not sure I'm actually using this, boot may be overriding it

(task-options!
 ; these are default arguments that are merged in whenever their respective tasks are called
 pom {:project 'myapp ; this is java magic and i don't know why I'm doing it
      :version "0.1.0"}
 jar {:main 'myapp.core}
 target {:dir #{"target/"}})

; these are the tasks which I want to run
(deftask build []
  (comp
   (aot :namespace #{'myapp.core}) ; I *think* this is needed to get a .class file for this ns into the jar
   (pom)
   (uber) ; unpacks all the dependencies into the output fileset
   (jar)  ; the file this creates is called "project.jar" no matter what the project was called
   (sift :include #{#"project.jar$"}) ; remove all the other files in the output fileset
   ;; requirement for the following step seems to have been added quite recently as I don't see it mentioned
   ;; in many web examples.  without it you will not get the target/ directory and will never be able to find
   ;; the generated example
   (target) ; save the output fileset 
   (install) ; I thnk this also puts stuff in your local maven (may be able to skip this)
   ))

core.clj

;; this is src/myapp/core.clj

(ns myapp.core (:gen-class)) ; gen-class is important

(defn -main []
  (println "hello world"))
  

Impressions of boot as a new user:

• I couldn't see anywhere obvious in the docs to tell me I needed to call (target)
• I missed :gen-class but I always forget that with leiningen too, so not boot's fault
• Having successfully avoided programming java pretty much ever since the time that applets were a thing, I have only the most superficial understanding of POMs and suchlike. I think this is required Because Reasons

To get the example to work, run

$ boot build

I have not (knowingly) used any plugins or middlewares or any other libraries here.