It is useful to cache html typically when you have lots of hits to the database, otherwise you shouldn't use html cache.
I recently needed to read the current url, extract a part of the url, and check the database for a hit on that pattern. This was done on every request and is something that suits caching. The data I was retrieving was something that was changed very rarely thus it could also be cached infinetly. For this purpose, I have chosen the in-built treecache that ships with JBoss and Seam.
Getting the url from a JSF page can be done like this:
HttpServletRequest request = (HttpServletRequest) FacesContext.getCurrentInstance().getExternalContext().getRequest();
String uri = request.getRequestURI();
// zero so that trailing empty strings will be discarded
String[] values = uri.split("/", 0);
//Concatinate the string and create a query based on the concatinated string
<s:cache region="instructionPageFragments" key="instruction-#{instructionHandler.instructionUrl}">
#{instructionHandler.getInstruction()}
</s:cache>
s:cache uses pojoCache internally, but we want to configure it to use treecache and that is done in components.xml.
You do this by defining the namespace
xmlns:cache="http://jboss.com/products/seam/cache"and then
<cache:jboss-cache-provider configuration="META-INF/treecache.xml">
<region name="/instructionPageFragments" policyClass="org.jboss.cache.eviction.LRUPolicy">
<attribute name="maxNodes">0</attribute>
<attribute name="timeToLiveSeconds">0</attribute>
<attribute name="maxAgeSeconds">0</attribute>
</region>
A copy of our entire treecache.xml is here:
<?xml version="1.0" encoding="UTF-8"?>
<!-- ===================================================================== -->
<!-- -->
<!-- Sample TreeCache Service Configuration -->
<!-- -->
<!-- ===================================================================== -->
<server>
<classpath codebase="../lib" archives="jboss-cache.jar, jgroups.jar"/>
<!-- ==================================================================== -->
<!-- Defines TreeCache configuration -->
<!-- ==================================================================== -->
<mbean code="org.jboss.cache.TreeCache"
name="jboss.cache:service=TreeCache">
<depends>jboss:service=Naming</depends>
<depends>jboss:service=TransactionManager</depends>
<!--
Configure the TransactionManager
-->
<attribute name="TransactionManagerLookupClass">org.jboss.cache.JBossTransactionManagerLookup</attribute>
<!--
Isolation level : SERIALIZABLE
REPEATABLE_READ (default)
READ_COMMITTED
READ_UNCOMMITTED
NONE
-->
<attribute name="IsolationLevel">REPEATABLE_READ</attribute>
<!--
Valid modes are LOCAL
REPL_ASYNC
REPL_SYNC
INVALIDATION_ASYNC
INVALIDATION_SYNC
-->
<attribute name="CacheMode">LOCAL</attribute>
<!--
Just used for async repl: use a replication queue
-->
<attribute name="UseReplQueue">false</attribute>
<!--
Replication interval for replication queue (in ms)
-->
<attribute name="ReplQueueInterval">0</attribute>
<!--
Max number of elements which trigger replication
-->
<attribute name="ReplQueueMaxElements">0</attribute>
<!-- Name of cluster. Needs to be the same for all clusters, in order
to find each other
-->
<attribute name="ClusterName">TreeCache-Cluster</attribute>
<!-- JGroups protocol stack properties. Can also be a URL,
e.g. file:/home/bela/default.xml
<attribute name="ClusterProperties"></attribute>
-->
<attribute name="ClusterConfig">
<config>
<!-- UDP: if you have a multihomed machine,
set the bind_addr attribute to the appropriate NIC IP address -->
<!-- UDP: On Windows machines, because of the media sense feature
being broken with multicast (even after disabling media sense)
set the loopback attribute to true -->
<UDP mcast_addr="228.1.2.3" mcast_port="48866"
ip_ttl="64" ip_mcast="true"
mcast_send_buf_size="150000" mcast_recv_buf_size="80000"
ucast_send_buf_size="150000" ucast_recv_buf_size="80000"
loopback="false"/>
<PING timeout="2000" num_initial_members="3"
up_thread="false" down_thread="false"/>
<MERGE2 min_interval="10000" max_interval="20000"/>
<!-- <FD shun="true" up_thread="true" down_thread="true" />-->
<FD_SOCK/>
<VERIFY_SUSPECT timeout="1500"
up_thread="false" down_thread="false"/>
<pbcast.NAKACK gc_lag="50" retransmit_timeout="600,1200,2400,4800"
max_xmit_size="8192" up_thread="false" down_thread="false"/>
<UNICAST timeout="600,1200,2400" window_size="100" min_threshold="10"
down_thread="false"/>
<pbcast.STABLE desired_avg_gossip="20000"
up_thread="false" down_thread="false"/>
<FRAG frag_size="8192"
down_thread="false" up_thread="false"/>
<pbcast.GMS join_timeout="5000" join_retry_timeout="2000"
shun="true" print_local_addr="true"/>
<pbcast.STATE_TRANSFER up_thread="true" down_thread="true"/>
</config>
</attribute>
<!--
Whether or not to fetch state on joining a cluster
NOTE this used to be called FetchStateOnStartup and has been renamed to be more descriptive.
-->
<attribute name="FetchInMemoryState">true</attribute>
<!--
The max amount of time (in milliseconds) we wait until the
initial state (ie. the contents of the cache) are retrieved from
existing members in a clustered environment
-->
<attribute name="InitialStateRetrievalTimeout">20000</attribute>
<!--
Number of milliseconds to wait until all responses for a
synchronous call have been received.
-->
<attribute name="SyncReplTimeout">20000</attribute>
<!-- Max number of milliseconds to wait for a lock acquisition -->
<attribute name="LockAcquisitionTimeout">15000</attribute>
<!-- Name of the eviction policy class. -->
<attribute name="EvictionPolicyClass"></attribute>
<!--
Indicate whether to use marshalling or not. Set this to true if you are running under a scoped
class loader, e.g., inside an application server. Default is "false".
-->
<attribute name="UseMarshalling">false</attribute>
<!-- Specific eviction policy configurations. -->
<attribute name="EvictionPolicyConfig">
<config>
<attribute name="wakeUpIntervalSeconds">120</attribute>
<!-- Cache wide default -->
<region name="/_default_"
policyClass="org.jboss.cache.eviction.LRUPolicy">
<!-- This is the maximum number of nodes allowed in this region. -->
<!-- 0 denotes no limit. -->
<attribute name="maxNodes">0</attribute>
<!-- The amount of time a node is not written to or read (in seconds) before the node is swept away.-->
<!-- 0 denotes no limit. -->
<attribute name="timeToLiveSeconds">0</attribute>
<!-- Lifespan of a node (in seconds) regardless of idle time before the node is swept away. -->
<!-- 0 denotes no limit. -->
<attribute name="maxAgeSeconds">0</attribute>
</region>
<!-- We dont have to define each region if we have default 0 values, but just incase we want to change it later -->
<!--
<region name="/instructionPageFragments" policyClass="org.jboss.cache.eviction.LRUPolicy">
<attribute name="maxNodes">0</attribute>
<attribute name="timeToLiveSeconds">0</attribute>
<attribute name="maxAgeSeconds">0</attribute>
</region>
<region name="/reviewInputPageFragments" policyClass="org.jboss.cache.eviction.LRUPolicy">
<attribute name="maxNodes">0</attribute>
<attribute name="timeToLiveSeconds">0</attribute>
<attribute name="maxAgeSeconds">0</attribute>
</region>
<region name="/actorPageFragments" policyClass="org.jboss.cache.eviction.LRUPolicy">
<attribute name="maxNodes">0</attribute>
<attribute name="timeToLiveSeconds">0</attribute>
<attribute name="maxAgeSeconds">0</attribute>
</region>
-->
</config>
</attribute>
</mbean>
<!-- Uncomment to get a graphical view of the TreeCache MBean above -->
<!-- <mbean code="org.jboss.cache.TreeCacheView" name="jboss.cache:service=TreeCacheView">-->
<!-- <depends>jboss.cache:service=TreeCache</depends>-->
<!-- <attribute name="CacheService">jboss.cache:service=TreeCache</attribute>-->
<!-- </mbean>-->
</server>
You can also programatically add and remove content to the cache.
@In
private CacheProvider cacheProvider;
//Removing the cache with the region instructionPageFragments, and the key instruction-'current url'
cacheProvider.remove("instructionPageFragments", "instruction-" + url);
//Adding to the cache
cacheProvider.put("instructionPageFragments", "instruction-" + url, "This text will be cached!!");
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