change compression level without losing the metadata of a jpg file

compress_jpg.clj

(ns sandbox.compress-jpg
  (meta {:description "change compression level without losing the metadata of a jpg file"
	 :url "http://blog.carsoncheng.ca/2011/02/how-to-change-jpeg-compression-in.html"})
  (:require clojure.java.io)
  (:import [javax.imageio IIOImage ImageIO]
	   [javax.imageio.plugins.jpeg JPEGImageWriteParam]))

(defn compress-jpg [inputFile outputFile compressionQuality]
  (let [image-reader (.next (ImageIO/getImageReadersByFormatName "jpg"))
	image-writer (.next (ImageIO/getImageWritersByFormatName "jpg"))]
    (try 
      (with-open [image-input-stream (ImageIO/createImageInputStream 
				      (clojure.java.io/file inputFile))
		  image-output-stream (ImageIO/createImageOutputStream 
				       (clojure.java.io/file outputFile))]
	(.setInput image-reader image-input-stream)
	(.setOutput image-writer image-output-stream)
	;; iio-image will contain the metadata
	(let [iio-image (IIOImage. (.read image-reader 0) nil
                                   (.getImageMetadata image-reader 0))
	      jpeg-params (doto (.getDefaultWriteParam image-writer)
			    (.setCompressionMode JPEGImageWriteParam/MODE_EXPLICIT)
			    ;; 0.7 is the new compression level [0..1]
			    (.setCompressionQuality compressionQuality))]
	  (.write image-writer nil iio-image jpeg-params)))
      (finally
       (do (.dispose image-writer)
	   (.dispose image-reader))))))

(comment
  (compress-jpg "path/to/inputFile.jpg" "path/to/outputFile.jpg" 0.7)
  ;; compress the input file so much, that it is obvious
  (compress-jpg "src/sandbox/inputFile.jpg" "src/sandbox/outputFile.jpg" 0.01))