Recipe 19.4 Changing the Order in Which Filters are Applied to Servlets

Problem

You want to change the order in which filters are applied to web components .

Solution

Change the order of filter-mapping elements in the deployment descriptor.

Discussion

The order of filter-mapping elements in web.xml determines the order in which the web container applies the filter to the servlet. Example 19-5 reverses the order of the filter-mapping elements that map two filters to the servlet named requestheaders , compared with Recipe 19.3. The LogFilter is thus applied to the servlet before the AuthenFilter . Any requests for the servlet pass through a chain: LogFilter AuthenFilter requestheaders servlet.

Example 19-5. Reversing the order of filter-mapping elements

 <!-- LogFilter applies to the requestheaders servlet  before AuthenFilter --> <filter-mapping>     <filter-name>LogFilter</filter-name>     <servlet-name>requestheaders</servlet-name> </filter-mapping> <filter-mapping>     <filter-name>AuthenFilter</filter-name>     <servlet-name>requestheaders</servlet-name> </filter-mapping> 

See Also

Recipe 7.9 on using a filter to read request parameter values; Recipe 11.11 on using a filter to monitor session attributes; Recipe 18.3 on using a filter to alter then forward the request; Recipe 19.1-Recipe 19.3 on mapping filters to web components; Recipe 19.5 on configuring filter init parameters; Recipe 19.6 on blocking requests; Recipe 19.7 on filtering the HttpServletResponse ; Recipe 19.8 on using filters with RequestDispatchers ; Recipe 19.9 on using filters to check request parameters; Recipe 19.10 on using filters to disallow requests from certain IP addresses.