int headerChecker=0;
for(Enumeration<String>names = request.getHeaderNames(); names.hasMoreElements(); ) {
    String name = (String)names.nextElement();
    if(name.equalsIgnoreCase("abcd")){
        headerChecker++; // add 1 to headerChecker if abcd header is encountered
    }
    for(Enumeration<String>values = request.getHeaders(name); values.hasMoreElements(); ) {
        String value=(String)values.nextElement();
        System.out.println("name: "+name+"tvalue: "+value);
        }
    }

    if(headerChecker! = 1){
        logger.error("abcd is duplicated, returning HTTP 404");
    } else {
        //...proceed with application
    }
}

name:  host   value: localhost:8080  name: user-agent value:
CocoaRestClient/8 CFNetwork/520.4.3 Darwin/11.4.2 (x86_64)
(MacBookPro9%2C2)  name: content-length value: 23  name: accept   value:

**name: abcd  value: 1234556**  name: accept-language value: en-us  name: accept-encoding value: gzip, deflate  name: content-type    value:
application/x-www-form-urlencoded  name: connection value: keep-alive

public class HeaderServlet extends HttpServlet
{
public void doPost(HttpServletRequest req, HttpServletResponse res)
{
    doGet(req, res);
}

public void doGet(HttpServletRequest req, HttpServletResponse res)
{
int xmsisdnChecker = 0;
String value = "";
for(Enumeration<String> names = req.getHeaderNames();names.hasMoreElements();){
    String name = (String) names.nextElement();
    Enumeration<String> values = req.getHeaders(name);
    if(values != null)
    {
        while(values.hasMoreElements()) {
            if(name.equalsIgnoreCase("abcd"))
            {
                xmsisdnChecker++;
                System.out.println("ee: " + xmsisdnChecker) ;
            }

            value = (String) values.nextElement();

            System.out.println("header name: " + name + "theader value: " + value);
        }

    }
  }
}
}