ioannis cherouvim

If you are using an entity as a named parameter in a hibernate Query or Criteria which is cachable from ehcache then this entity needs to implement hashcode and equals using a business key. Otherwise the hibernate Query or Criteria may always “look different” to ehcache so it will be a constant cache miss.

DEBUG (MemoryStore.java:138) - query.FooBarCache: query.FooBarMemoryStore miss for sql: /* criteria query */ select this_.id as y0_ from foobars this_ where this_.state=?; parameters: LIVE; max rows: 1; transformer: org.hibernate.transform.PassThroughResultTransformer@294633f0
DEBUG (Cache.java:808) - query.FooBar cache - Miss

If you experience the following warning in your hibernate+ehcache application:

2008-11-20 13:02:42,937 WARN  (CacheManager.java:322) -
  Creating a new instance of CacheManager using the diskStorePath
  "D:\apache-tomcat-5.5.26\temp" which is already used by an
  existing CacheManager.
The source of the configuration was classpath.
The diskStore path for this CacheManager will be set to
  D:\apache-tomcat-5.5.26\temp\ehcache_auto_created_1227178962937.
To avoid this warning consider using the CacheManager factory
  methods to create a singleton CacheManager or specifying a
  separate ehcache configuration (ehcache.xml) for each
  CacheManager instance.

then you need to set the following in your hibernate.cfg.xml file:

<property name="hibernate.cache.provider_class">
  net.sf.ehcache.hibernate.SingletonEhCacheProvider
</property>

Ehcache Hibernate documentation

When an http request to your /rss page needs 400 milliseconds to complete, it seems obvious that your website could benefit from some caching. Ehcache is a well known cache provider, which most of us know from hibernate. Since we are already “bound” to ehcache, lets see how we can benefit from caching some dynamically generated pages:

web.xml

<filter>
  <filter-name>SimplePageCachingFilter</filter-name>
  <filter-class>net.sf.ehcache.constructs.web.filter.SimplePageCachingFilter</filter-class>
</filter>
<filter-mapping>
  <filter-name>SimplePageCachingFilter</filter-name>
  <url-pattern>/rss</url-pattern>
</filter-mapping>

We set up the SimplePageCachingFilter in the web.xml of the web application and map it to one or more url patterns or servlets. All requests to /rss will be intercepted by the SimplePageCachingFilter.

ehcache.xml

<ehcache>
  <diskStore path="java.io.tmpdir" />
  <cache name="SimplePageCachingFilter"
         maxElementsInMemory="0"
         eternal="false"
         timeToIdleSeconds="600"
         timeToLiveSeconds="600"
         overflowToDisk="true"/>
</ehcache>

We then configure the cache region for pages. We don’t want any elements kept in memory. Everything should be written to disk at the java.io.tmpdir location. The cache expires every 10 minutes.

Now hitting http://example.com/rss (our default rss page) results in a cache miss. The content is being generated from scratch but before returning to the client, the filter stores it locally. The second time we’ll get a cache hit. The content now is being fetched from the cache and its very fast. 10 minutes later this cache element will be invalidated. Note that the default implementation uses the URI together with the query string to calculate the cache key, so /rss?type=news and /rss?type=forum will result in two different cache elements.