Example: Configuring the dynamic cache

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

Suppose that a servlet is used to manage a simple news site. This servlet uses the query parameter "action" to determine if the request is being used to "view" news or "update" news (used by the administrator). Another query parameter "category" is used to select 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 dynamic cache for this example with the cachespec.xml file:

Define the <cache-entry> elements necessary to identify the servlet. In this case, the servlet's URI is "newscontroller" so this is the cache-entry's <name> element. Because this example caches a servlet or JavaServer Pages (JSP) file, the cache entry class is "servlet".
```
<cache-entry> 
<name> /newscontroller </name>
<class>servlet  </class>  
 </cache-entry>
```

Define cache ID generation rules. This servlet is cached 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. Finally, the optional session attribute for the user's layout is included in the cache ID. The cache entry now is :

<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>

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>

Define invalidation rules. Since a category dependency ID is already defined, define an invalidation rule to invalidate the category when action=update. To incorporate the conditional logic, we will 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 is created and run. The final cache-entry now looks like this:

<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>