Browser/Device detection with Freemarker

Freemarker lets you grab HTTP headers, so you could do something with User-Agent:

<#assign ua = http.request.getHeader("User-Agent") />

I know this is a super old thread, but I wanted to share some info that will hopefully help anyone that ends up needing to accomplish the same thing.

We needed to display a banner on certain pages in our environment that are not working properly in Internet Explorer so that we could inform users to switch to a different browser if they experienced issues. 

So to accomplish this in FreeMarker (since we ran into other compatibility issues when attempting to use jQuery) with the method provided in the comment from xorrkaz above, I created some functions in a macro file (which can be downloaded here on GitHub) that allow us to quickly fingerprint the browser to find out the browser and operating system information.

Here is an example of how we it can be used:

<#-- Import dependencies -->
<#import 'custom.macro.browser' as browserDetect />

<#-- Get the browser information -->
<#assign browserInfo = browserDetect.getBrowserInfo() />

<#-- Display the browser and operating system info -->
Browser (Base): ${browserInfo.base!"unknown"}<br />
Browser (Specific): ${browserInfo.specific!"unknown"}<br />
Operating System: ${browserInfo.os!"unknown"}

The code sample above would return something like this:

Browser (Base): Internet Explorer
Browser (Specific): Internet Explorer 11
Operating System: Windows 10

We were then able to create our compatibility warning banner component and wrap it in an if statement like this:

<#if browserInfo.base?? && (browserInfo.base == "Internet Explorer" || browserInfo.base == "Edge (Legacy)")>
  <#-- Display the banner -->
</#if>

I hope this helps anyone looking to accomplish something like this.  Enjoy!