title: Formatting ISO 8601 date with a colon seperator
body: <p>I am trying to convert the date in milliseconds to the following ISO 8601 format:</p>
  
  <p><img src="https://i.stack.imgur.com/PrWGv.jpg" alt="enter image description here"></p>
  
  <p>But I am getting the following using SimpleDateFormat:</p>
  
  <pre><code>    /**
       * It converts the time from long to the ISO format
       * 
       * @param timestampMillis
       * @return isoDate
       */
      public String convertTimeMillisToISO8601(String timestampMillis)
      {
          long timeInLong= Long.parseLong(timestampMillis);
          DateFormat df = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ssZ");
          df.setTimeZone(TimeZone.getTimeZone("UTC"));
          String isoDate = df.format(new java.util.Date(timeInLong));
          return isoDate;
      }
  </code></pre>
  
  <p><strong>OUTPUT:</strong></p>
  
  <pre><code>"ts":"2015-06-18T09:56:21+0000"
  </code></pre>
  
  <p>I know I can use substring to append the extra colon but Is there any better way to do so ?</p>