java-case

A simple utility library for selecting different forms depending on the Java major version. In case the Clojure needs to run on multiple JDK platforms, this can make things more concise.

Releases and Dependency Information

Latest stable release: 1.1

CLI/deps.edn dependency information:

org.clojars.jeff_evans/java-case {:mvn/version "1.1"}

Leiningen dependency information:

[jeff_evans/java-case "1.1"]

This library is not yet deployed to Maven central.

Usage Examples

; assume java.security.KeyStore has been imported
(defn file->keystore
  "Initializes a Java KeyStore from the given filename and password."
  [filename password]
  ;; Java 9 adds a getInstance override to initialize directly
  ;; in older versions, it takes multiple steps
  (java-case/java-case
    "9+" (KeyStore/getInstance (io/file filename) password)
    (doto (KeyStore/getInstance (KeyStore/getDefaultType))
      (.load (io/input-stream (str "file:/" filename)) password))))

(defn instant->local-time
  "Converts the given instant to a LocalTime."
  [instant]
  ;; ofInstant came to LocalTime only JDK 9
  (java-case/java-case
    "9+" (LocalTime/ofInstant instant (ZoneId/of "UTC"))
    (let [ldt (LocalDateTime/ofInstant instant (ZoneId/of "UTC"))]
      (.toLocalTime ldt))))

The version expressions can be Strings ending in +, in which case intermediate JDK versions are filled in. The order doesn't matter.

(macroexpand-1 '(java-case/java-case
                  "11+"  "Java 11 through 16"
                  "17"   "Java 17!"
                  "1.8+" "Java 1.8 through 10"
                  1.7    "Java 1.7, for some reason"
                  "20+"  "Java 20 and beyond"))
=>
(clojure.core/case
  (clojure.core/or
    us.jeffevans.java-case/*java-spec-version-override*
    (us.jeffevans.java-case/current-java-spec-version))
  ("11" "12" "13" "14" "15" "16")
  "Java 11 through 16"
  "17"
  "Java 17!"
  ("1.8" "9" "10")
  "Java 1.8 through 10"
  "1.7"
  "Java 1.7, for some reason"
  "20"
  "Java 20 and beyond")

Future Proof

This library attempts to be future proof, to support major Java versions that may be released after its latest release. Suppose K=J+1, and you have a clause for J+. At macro expansion time, the Clojure compiler detects the Java version is K (via the JVM property). This clause should work as expected. However, I haven't thought of the best way to comprehensively test this (suggestions welcomed).

In any case, you can always just use the default clause to specify the "latest" form.

Building and Testing

This project was created with https://github.com/seancorfield/clj-new

Run the project's tests

$ clojure -T:build test

Run the project's CI pipeline and build a JAR

$ clojure -T:build ci

This will produce an updated pom.xml file with synchronized dependencies inside the META-INF directory inside target/classes and the JAR in target. You can update the version (and SCM tag) information in generated pom.xml by updating build.clj.

Install it locally (requires the ci task be run first):

$ clojure -T:build install

Deploy it to Clojars -- needs CLOJARS_USERNAME and CLOJARS_PASSWORD environment variables (requires the ci task be run first):

$ clojure -T:build deploy

License

Copyright © 2021 Jeff Evans

Distributed under the Eclipse Public License version 1.0.