Spring Cache Abstraction Using Ehcache - The Story of Experiments with Technology

In this article, we will see how to use EhCahce with Spring Cache abstraction. Refer http://ehcache.org/documentation/recipes/spring-annotations for using EhCache’s own annotations. The advantage of using it with Spring Cache abstraction is that it’s easy to change the underlying storage. Say in future if we want to change it to Memcached, then it is just a configuration change and not a code change.

Let’s look at the Spring configuration steps and common issues that one encounters while using Spring Cache.

Add the Ehcache dependency to the project

<dependency> <groupId>net.sf.ehcache</groupId> <artifactId>ehcache-core</artifactId> <version>2.3.1</version> </dependency>

Note: Without adding the dependency you might see the error

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping#0': Invocation of init method failed; nested exception is java.lang.NoClassDefFoundError: Lnet/sf/ehcache/CacheManager;

Include the cache namespace and schema location in the Spring Configuration file.

<beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:cache="http://www.springframework.org/schema/cache" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/cache http://www.springframework.org/schema/cache/spring-cache.xsd"> </beans>

Configure the application to use annotation driven

Define the cacheManager bean

<bean id="cacheManager" class="org.springframework.cache.ehcache.EhCacheCacheManager"> <property name="cacheManager" ref="ehcache"/> </bean>  <bean id="ehcache" class="org.springframework.cache.ehcache.EhCacheManagerFactoryBean"> <property name="configLocation" value="classpath:ehcache.xml"/> </bean>

Configure the ehcache.xml Defined the caches in the ehcache configuration XML. Below is the sample ehcache xml file to define the caches.

<ehcache xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="http://ehcache.org/ehcache.xsd" updateCheck="false" maxBytesLocalHeap="1g" maxBytesLocalOffHeap="4g" maxBytesLocalDisk="100g" > <defaultCache maxElementsInMemory="5" eternal="false" timeToIdleSeconds="20" timeToLiveSeconds="20" overflowToDisk="false" diskPersistent="false" memoryStoreEvictionPolicy="LRU"/> <cache name="longCache" timeToLiveSeconds="10000"/> </ehcache>

Note: Without defaultCache defined, below error will be thrown

Cannot resolve reference to bean 'cacheManager' while setting bean property 'cacheManager'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'cacheManager' defined in ServletContext resource [/WEB-INF/servlet-config.xml]: Cannot resolve reference to bean 'ehcache' while setting bean property 'cacheManager'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'ehcache' defined in ServletContext resource [/WEB-INF/servlet-config.xml]: Invocation of init method failed; nested exception is net.sf.ehcache.CacheException: Illegal configuration. No default cache is configured.

Add the @Cacheable annotation to the code

import org.springframework.cache.annotation.Cacheable; . . @Cacheable("longCache") public List<Product> getAllProducts(final int pageNumber) { System.out.println("Inside DAO so cache did not get used"); // TODO Auto-generated method stub Query query = getEntityManager().createQuery("SELECT p FROM Product p"); return query.setFirstResult(pageNumber * PAGE_SIZE) .setMaxResults(PAGE_SIZE).getResultList(); }

Common issues one might face in using the Spring Cache abstraction

Cache key collision: The default key generator is a simple one and it is easy to get key collisions using this. Refer the DefaultKeyGenerator.java code to see how it works. Also when you have an array as a parameter, the default key generator produces different key for each execution.

It’s better to use your own key generator. Below is the sample one I used

import org.apache.commons.lang3.builder.HashCodeBuilder; import org.springframework.cache.interceptor.KeyGenerator; public class CacheKeyGenerator implements KeyGenerator { @Override public Object generate(Object o, Method method, Object... objects) { HashCodeBuilder hashCodeBuilder = new HashCodeBuilder(); hashCodeBuilder.append(method.getName()); for (Object object : objects) { hashCodeBuilder.append(object); } return hashCodeBuilder.toHashCode(); } }

And you can set this as your default key generator in the Spring configuration file like below.

<cache:annotation-driven cache-manager="cacheManager" key-generator="cacheKeyGenerator"/> <bean id="cacheKeyGenerator" class="com.meygam.cache.CacheKeyGenerator"/>

Application context is loaded more than once:

Sometimes due to misconfiguration the application context gets loaded twice and due to that you might get the error. Make sure you name the cacheManager in the ehcache.xml and you are not loading the application context twice.

Another unnamed CacheManager already exists in the same VM. 
Please provide unique names for each CacheManager in the config or do one of following:
1. Use one of the CacheManager.create() static factory methods to reuse same CacheManager with same name or create one if necessary
2. Shutdown the earlier cacheManager before creating new one with same name.
The source of the existing CacheManager is: InputStreamConfigurationSource [stream=sun.net.www.protocol.jar.JarURLConnection$JarURLInputStream@47f3ed6]

Common issues one might face in using the Spring Cache abstraction

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