Recipe 3.2 Creating More Than One Mapping to a Servlet

Problem

You want to create several names or URL patterns that web users can use to request a single servlet.

Solution

Associate the servlet element with more than one servlet-mapping element in the deployment descriptor.

Discussion

You can create a number of servlet-mapping elements for a single servlet, as shown in Example 3-2. A user can access this servlet by using one of two addresses: http://www.mysite.org/cookbook/cookieservlet or http://www.mysite.org/cookbook/mycookie .

Example 3-2. Two servlet-mapping tags

 <?xml version="1.0" encoding="ISO-8859-1"?> <!DOCTYPE web-app     PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"            "http://java.sun.com/dtd/web-application_2_3.dtd" > <web-app>   <servlet>     <servlet-name>CookieServlet</servlet-name>     <servlet-class>com.parkerriver.cookbook.CookieServlet</servlet-class>   </servlet>   <servlet-mapping>     <servlet-name>CookieServlet</servlet-name>     <url-pattern>/cookieservlet</url-pattern>   </servlet-mapping>   <servlet-mapping>     <servlet-name>CookieServlet</servlet-name>     <url-pattern>/mycookie</url-pattern>   </servlet-mapping> </web-app>

Remember that the servlet-mapping elements have to appear after all of the servlet elements in the servlet 2.3 deployment descriptor.

Only exact matches to the URL pattern will work. If a user requests /cookieservlet/ (note the final forward slash) instead of /cookieservlet , she receives an HTTP error code instead of the servlet-generated page she was expecting.

You can use a wildcard character ( * ) to extend your mapping pattern. The mappings in Example 3-3 invoke the CookieServlet for all of the URLs that begin with /cookie/ , and then optionally include any names after the forward slash. For example, CookieServlet can be invoked with a URL of http://www.mysite.org/cookbook/cookie/you using this descriptor. This is because the url-pattern matches any HTTP requests ending with the "/cookie/" string.

Example 3-3. Using an asterisk in the URL pattern

 <?xml version="1.0" encoding="ISO-8859-1"?> <!DOCTYPE web-app     PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"            "http://java.sun.com/dtd/web-application_2_3.dtd" > <servlet>   <servlet-name>CookieServlet</servlet-name>   <servlet-class>com.jspservletcookbook.CookieServlet</servlet-class> </servlet> <servlet-mapping>   <servlet-name>CookieServlet</servlet-name>   <url-pattern>/cookie/*</url-pattern> </servlet-mapping>

You cannot use the asterisk character as a wildcard symbol inside the servlet-name element. The asterisk can be used only as a wildcard symbol in the url-pattern element (as in <url-pattern>/cookie/*</url-pattern>) , or in patterns that point to all files with a certain extension or suffix (as in <url-pattern>*.jsp</url-pattern>) . The latter pattern is called an extension mapping .