JSP Cache Tags

JSP cache tags enable you to cache JSP page fragments within the Java engine. Each fragment can be cached using different cache criteria. For example, suppose you have page fragments to view stock quotes and weather information. The stock quote fragment can be cached for 10 minutes, the weather report fragment for 30 minutes, and so on.

For more information about response caching as it pertains to servlets, see Caching Servlet Results.

JSP caching uses the custom tag library support provided by JSP 2.0. JSP caching is implemented by a tag library packaged into the install_dir/lib/.jar file, which is always on the server classpath. The sun-web-cache.tld tag description file is in the install_dir/lib/tlds directory and can be copied into the WEB-INF directory of your web application.

JSP caching is available in three different scopes: request, session, and application. The default is application.

To use a cache with the request scope, a web application must specify the com.sun.appserv.web.taglibs.cache.CacheRequestListener in its deployment descriptor, as follows:

<listener>
   <listener-class>
      com.sun.appserv.web.taglibs.cache.CacheRequestListener
   </listener-class>
</listener>
  

To use a cache in session scope, a web application must specify the com.sun.appserv.web.taglibs.cache.CacheSessionListener in its deployment descriptor, as follows:

<listener>
   <listener-class>
      com.sun.appserv.web.taglibs.cache.CacheSessionListener
   </listener-class>
</listener>
  

To use a cache with the application scope, a web application does not need to specify any listener. The com.sun.appserv.web.taglibs.cache.CacheContextListener is already specified in the sun-web-cache.tld file.

The JSP cache tags are as follows:

• cache Tag

• flush Tag

cache Tag

The cache tag enables you to cache fragments of your JSP pages. It caches the body between the beginning and ending tags according to the attributes specified. The first time the tag is encountered, the body content is executed and cached. Each subsequent time is run, the cached content is checked to see whether it needs to be refreshed. If so, it is executed again, and the cached data is refreshed. Otherwise, the cached data is served.

Attributes

The following table describes attributes for the cache tag.

Example

The following example represents a cached JSP page.

<%@ taglib prefix="mypfx" uri="/com/sun/web/taglibs/cache" %>
			<%
   		String cacheKey = null;
    		if (session != null)
      	cacheKey = (String)session.getAttribute("loginId");
   		// check for nocache
			   boolean noCache = false;
   		String nc = request.getParameter("nocache");
   		if (nc != null)
      	noCache = "true";
			   // force reload
			   boolean reload=false;
			   String refresh = request.getParameter("refresh");
			   if (refresh != null)
     		reload = true;
			 %>
			 <mypfx:cache key="<%= cacheKey %/>" nocache="<%= noCache %/>" 
       refresh="<%= reload %/>" timeout="10m"/>
			<%
		  	   String page = request.getParameter("page");
   		if (page.equals("frontPage") {
       	// get headlines from database
		    } else {
       .....
			 %>
				</mypfx:cache/>
							<mypfx:cache timeout="1h"/>
				<h2> Local News </h2>
			<%
			   // get the headline news and cache them
			%>
				</mypfx:cache/>

flush Tag

This tag forces the cache to be flushed. If a key is specified, only the entry with that key is flushed. If no key is specified, the entire cache is flushed.

Attributes

The following table describes attributes for the flush tag. The left column lists the attribute name, the middle column indicates the default value, and the right column describes what the attribute does.

Examples

To flush the entry with key="foobar":

<mypfx:flush key="foobar"/>

         

To flush the entire cache:

<% if (session != null && session.getAttribute("clearCache") != null) { %/>
     <mypfx:flush />
 <% } %/>