Example: Configuring the dynamic cache service

This example puts all of the steps together for configuring the dynamic cache service with the cachespec.xml file, showing the use of the cache ID generation rules, dependency IDs, and invalidation rules.

Suppose that a servlet manages a simple news site. This servlet uses the query parameter "action" to determine if the request views (query parameter "view") news or updates (query parameter "update") news (used by the administrator). Another query parameter "category" selects the news category. Suppose that this site supports an optional customized layout that is stored in the user's session using the attribute name "layout". Here are example URL requests to this servlet:

http://yourhost/yourwebapp/newscontroller?action=view&category=sports (Returns a news page for the sports category )

http://yourhost/yourwebapp/newscontroller?action=view&category=money (Returns a news page for the money category)

http://yourhost/yourwebapp/newscontroller?action=update&category=fashion (Allows the administrator to update news in the fashion category)

Here are the steps for configuring the dynamic cache service for this example with the cachespec.xml file:

1. Define the <cache-entry> elements that are necessary to identify the servlet. In this case, the URI for the servlet is "newscontroller", so this is the cache-entry <name> element. Because this example caches a servlet or JavaServer Pages file, the cache entry class is "servlet".

   <cache-entry> 
   <name> /newscontroller </name>
   <class>servlet  </class>  
    </cache-entry>

2. Define cache ID generation rules. This servlet caches only when action=view, so one component of the cache ID is the parameter "action" when the value equals "view". The news category is also an essential part of the cache ID. The optional session attribute for the user's layout is included in the cache ID. The cache entry is now:

   <cache-entry> 
    <name> /newscontroller </name>
    <class>servlet  </class>  
     <cache-id>
     <component id="action" type="parameter">
      <value>view</value>
      <required>true</required>
     </component>
     <component id="category" type="parameter">
      <required>true</required>
     </component>
     <component id="layout" type="session">
      <required>false</required>
     </component>
    </cache-id>
   </cache-entry>

3. Define dependency ID rules. For this servlet, a dependency ID is added for the category. Later, when the category is invalidated due to an update event, all views of that news category are invalidated. Following is an example of the cache entry after adding the dependency ID:

   <cache-entry> 
    <name>newscontroller </name>
    <class>servlet  </class>  
     <cache-id>
     <component id="action" type="parameter">
      <value>view</value>
      <required>true</required>
     </component>
     <component id="category" type="parameter">
      <required>true</required>
     </component>
     <component id="layout" type="session">
      <required>false</required>
     </component>
    </cache-id>
    <dependency-id>category
     <component id="category" type="parameter">
      <required>true</required>
     </component>
    </dependency-id>
   </cache-entry>
   

4. Define invalidation rules. Because a category dependency ID is already defined, define an invalidation rule to invalidate the category when action=update. To incorporate the conditional logic, add "ignore-value" components into the invalidation rule. These components do not add to the output of the invalidation ID, but only determine whether or not the invalidation ID creates and runs. The final cache-entry now looks like the following:

   <cache-entry> 
    <name>newscontroller </name>
    <class>servlet  </class>  
     <cache-id>
     <component id="action" type="parameter">
      <value>view</value>
      <required>true</required>
     </component>
     <component id="category" type="parameter">
      <required>true</required>
     </component>
     <component id="layout" type="session">
      <required>false</required>
     </component>
    </cache-id>
    <dependency-id>category
     <component id="category" type="parameter">
      <required>true</required>
     </component>
    </dependency-id>
    <invalidation>category
     <component id="action" type="parameter" ignore-value="true">
      <value>update</value>
      <required>true</required>
     </component>
     <component id="category" type="parameter">
      <required>true</required>
        </component>
    </invalidation>
   </cache-entry>

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