How to read a whole binary file (Nippy) into byte array in Clojure?

Question

I need to convert Nippy data structures stored on disk into something that can be read by Nippy? Nippy uses byte arrays, so I need some way to convert the file into a byte a

Answer 1

Since you know the .length of the file, you can allocate once and use DataInputStream's readFully method. No additional libraries, buffer copies, or loops required.

(defn file-to-byte-array
  [^java.io.File file]
  (let [result (byte-array (.length file))]
    (with-open [in (java.io.DataInputStream. (clojure.java.io/input-stream file))]
      (.readFully in result))
    result))