Pretty Printing XML with Clojure

The other day, I did some XML cleanup. I am posting the snippet here for safekeeping purposes in case I need to refer to it later. 

(defn ppxml [xml]
  (let [in (javax.xml.transform.stream.StreamSource.
            (java.io.StringReader. xml))
        writer (java.io.StringWriter.)
        out (javax.xml.transform.stream.StreamResult. writer)
        transformer (.newTransformer 
                     (javax.xml.transform.TransformerFactory/newInstance))]
    (.setOutputProperty transformer 
                        javax.xml.transform.OutputKeys/INDENT "yes")
    (.setOutputProperty transformer 
                        "{http://xml.apache.org/xslt}indent-amount" "2")
    (.setOutputProperty transformer 
                        javax.xml.transform.OutputKeys/METHOD "xml")
    (.transform transformer in out)
    (-> out .getWriter .toString)))

Now you can pass your XML string, 

(ppxml "<root><child>aaa</child><child/></root>")

and get the pretty printed version, 

<?xml version="1.0" encoding="UTF-8"?>
<root>
  <child>aaa</child>
  <child/>
</root>

You can also use it to pretty print Compojure output either manually, 

(ppxml (html
        [:html
         [:head
          [:title "Hello World"]]
         [:body "Hello World!"]]))

or using a middleware, 

(defn with-ppxml [handler]
  (fn [request]
    (let [response (handler request)]
      (assoc response :body (ppxml (:body response))))))

and have your pretty printed HTML, 

<html> 
  <head> 
    <title>Hello World</title> 
  </head> 
  <body>Hello World!</body> 
</html>
Tags: clojure compojure xml