Fix Java middleware example (#358)

* Add encoding/decoding HTTP msgs to Java middleware example.

* Add clojure middleware example.

examples/middleware/echo.clj

@@ -0,0 +1,53 @@
+(ns echo.core
+  (:gen-class)
+  (:require [clojure.string :as cs]
+            [clojure.java.io :as io])
+  (:import org.apache.commons.codec.binary.Hex
+           java.io.BufferedReader
+           java.io.IOException
+           java.io.InputStreamReader))
+
+
+(defn transform-http-msg
+  "Function that transforms/filters the incoming HTTP messages."
+  [headers body]
+  ;; do actual transformations here
+  [headers body])
+
+
+(defn decode-hex-string
+  "Decode an Hex-encoded string."
+  [s]
+  (String. (Hex/decodeHex (.toCharArray s))))
+
+
+(defn encode-hex-string
+  "Encode a string to a hex-encoded string."
+  [^String s]
+  (String. (Hex/encodeHex (.getBytes s))))
+
+
+(defn -main
+  [& args]
+  (let [br (BufferedReader. (InputStreamReader. System/in))]
+    (try
+      (loop [hex-line (.readLine br)]
+        (let [decoded-req (decode-hex-string hex-line)
+
+              ;; empty line separates headers from body
+              http-request (partition-by empty? (cs/split-lines decoded-req))
+              headers (first http-request)
+
+              ;; HTTP messages can contain no body:
+              body (when (= 3 (count http-request)) (last http-request))
+              [new-headers new-body] (transform-http-msg headers body)]
+
+          (println (encode-hex-string (str (cs/join "\n" headers)
+                                           (when body
+                                             (str "\n\n"
+                                                  (cs/join "\n" body)))))))
+        (when-let [line (.readLine br)]
+          (recur line)))
+      (catch IOException e nil))))
+
+