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.

See Also

Chapter 1 on web.xml; Recipe 3.1; Recipe 3.3-Recipe 3.8; Chapter 11 of the Servlet v2.3 and 2.4 specifications on mapping requests to servlets.