title: How to convert Map<String,String> to "key1:value1,key2:value2,.." using lambda
body: <p>I have a <code>Map&lt;String,String&gt;</code> and I need to convert it to a single <code>String</code>: <code>"key1:value1,key2:value2,..."</code>.</p>
  
  <p>I can do this using iteration. But can I do this using new lambda and stream functionality of java 8? Thanks!</p>