In a module of my application, a complex query is very slow. It needs about 5 seconds because the application gets data from nearly 10 tables. Most of the 10 tables are not updated often. Therefor I decided to use cache for the 10 tables.
Software: Spring+hibernate
ehcache is the default cache for hibernate. So I choosen it.

Step1.  Modify ehcache.xml in /webroot/web-inf/classes. the content is below:
            
           <ehcache>
                <diskStore path="java.io.tmpdir" />
                <defaultCache maxElementsInMemory="10000" eternal="false"
                    overflowToDisk="true" timeToIdleSeconds="120" timeToLiveSeconds="120"
                    diskPersistent="false" diskExpiryThreadIntervalSeconds="120" />
            </ehcache>

Step2. Configure applicationContext-hibernate.xml in the spring framework.
             .....
            <bean id="sessionFactory" class="org.springframework.orm.hibernate3.LocalSessionFactoryBean">       
                 .....
                     <prop key="connection.provider_class">org.hibernate.connection.C3P0ConnectionProvider</prop>
                    <prop key="hibernate.cache.use_query_cache">true</prop>
                    <prop key="hibernate.cache.provider_class">org.hibernate.cache.EhCacheProvider</prop>
                 ...
            </bean>

Step3. Configure the hibernate mapping file(ie. *.hbm.xml), add a new attribute:
            <cache usage="read-only"/>

Step 4. Change the dao. Before it retireves data, it will be asked to use cache, for example:
                   getHibernateTemplate().setCacheQueries(true);
               or
                   query.setCacheable(true)

Now, everything looks very good. It only need less than 1 second to get all the data. Much faster than before.