JSP provides us with access objects that we can use to get information from the incoming request and modify the resulting response. This makes it possible for us to do things like identify what type of browser is making the request. We can then set up a different type of request based upon what that browser supports.

The following example determines whether the incoming browser is Internet Explorer, Netscape, or a WML client (like a cell phone). Depending on the browser it finds, it returns an appropriate greeting. Let's take a gander at an example of this at work. (Note: I'm going to use line numbering here because it makes the explanation of the example so much easier, but it isn't part of the code -- it's just there for reference.)

Browser Detection in JSP
<%@ page info="Greetings" errorPage="err.jsp" %>

This first line simply adds some arbitrary information to the generated servlet and tells the Web server to redirect any Java errors encountered on the page to the err.jsp page. Other things that can be done in this page directive include importing various Java APIs.

<%! public final static int IE = 0; public final static int NETSCAPE = 1; public final static int WML = 2; public int getBrowser(HttpServletRequest request) { String accept = request.getHeader("ACCEPT"); if (null != accept && -1 != accept.indexOf("wml")) { return WML; } String agent = request.getHeader("USER-AGENT"); if (null != agent && -1 != agent.indexOf("MSIE")) { return IE; } return NETSCAPE; } %>

This section of code declares three static values that represent the different browser types we are detecting. It also defines the getBrowser() method that accepts the request object and uses it to determine what browser has made the request. It does so by looking at the ACCEPT HTTP request header to see if the browser will accept wml. If it doesn't, it then looks at the USER-AGENT HTTP request header to see if it contains "MSIE." If it does, then the browser making the request is IE. Otherwise, we assume it's a Netscape browser.

<%
   switch (getBrowser(request)) {
   case WML:
     response.setContentType("text/vnd.wap.wml");
%>

<?xml version="1.0"?>
<wml>
<card id="index" title="Browser Greeting">
<p align="center">Hello, Wireless Fan!</p>

</card>
</wml>
<%
     break;
   case IE:
%>
<HTML><BODY><H1>Hello, IE
Fan!</H1></BODY></HTML>
<%
     break;
   default:
%>
<HTML><BODY><H1>Hello, Netscape
Fan!</H1></BODY></HTML>

<%
   }
%>

In the last section of code, we used the declared getBrowser() method in a Java switch statement to determine what should be returned to the browser. For IE and Netscape browsers, a simple HTML document is returned. For WML-accepting browsers, the content type of the response is set to text/vnd.wap.wml and a WML document is returned.

In these very meaningful forty-two lines of code, we have a simple page that will serve up a pleasant greeting to three different browsers. If all has gone well, creating this code should have whetted your appetite for more. If you're interested in pushing JSP even further, then read on for a list of additional resources you can use to expand your JSP horizons.

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Web Hosting Tips for Webmasters - JSP Browser Detection

Web Hosting Tips for Webmasters -
JSP Browser Detection