CODEWITHSUNDEEP
httpservletshttp-redirectservlet-filtersuser-agent
Nirmal Patel
Nirmal Patel

Reputation: 5168

Correct way to Redirect based on browser user-agent?

I am building a Spring MVC based application where I want to redirect user's to specific portion of the site based on their browser.

I am using a Filter applied to /site/home.jsp to read the User-Agent to determine the browser type. 

HttpServletRequest req = (HttpServletRequest) request;
String uaString = req.getHeader("User-Agent");

Further I want to redirect users as below:

My confusion is what is the correct way to redirect the user from my BrowserDetector filter?

1) Simply redirect the user?

resp.sendRedirect("/AppName/site/ie/home.jsp");

2) Use an HTTP Temp redirect?

resp.setStatus(HttpServletResponse.SC_TEMPORARY_REDIRECT);
resp.setHeader("Location", "/AppName/site/ie/home.jsp");

3) Server side redirect?

RequestDispatcher request_Dispatcher=request.getRequestDispatcher("/ie/home.jsp");
request_Dispatcher.forward(request,response);

4) Any other correct way?

Upvotes: 1

Views: 7291

Answers (2)

cdeszaq
cdeszaq

Reputation: 31280

First and foremost: DON'T DO SERVER-SIDE BROWSER SNIFFING!

Server-side browser sniffing is a bad idea for a bunch of different reasons, but here's just a few of them:

  1. There are hundreds of different browsers and that number changes all the time, so detecting them all is a race you can't win
  2. Search engines really don't like it when you give them different stuff than you give to real browsers (and they do test it)
  3. It doesn't reliably tell you the capabilities of the user's browser because they may have spoofed their user agent string (for various reasons) or may have other things installed that increase or decrease the capabilities their indicated browser has natively

A much better approach is to use Progressive Enhancement or Graceful Degradation.

That being said, one option that works more reliably is to do the sniffing in the browser and then redirect them client-side accordingly. Modernizr will tell you what capabilities their browser has, and from there you can decide what to serve them.

Upvotes: 1

DaveRandom
DaveRandom

Reputation: 88647

Idea number 3 is probably a bad idea, as it will most likely result in you having to perform this check for every request, which is inefficient (only slightly, but small inefficiencies can mount up).

Idea's number 1 & 2 are also not the best approach, because both will result in a Temporary redirect (307) response, wheras what you probably want is a permanent redirect (301). This is because the browser in question will always be the same - FF and IE never share there list of permanent moves, so even if both browsers are used by the same client machine this will not cause a problem. You should use 301 for reasons of, again, efficiency - if the browser always goes directly to the correct place, it is less work for your server to do.

To sum up, I think idea 2 is the closest, but you should use this instead:

resp.setStatus(HttpServletResponse.SC_MOVED_PERMANENTLY);
resp.setHeader("Location", "/AppName/site/ie/home.jsp");

Keep in mind that User-Agent strings can be spoofed and cannot be 100% relied upon.

This is my personal opinion, YMMV...

Upvotes: 3

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