Spring annotations and Ehcache

Ehcache-spring-annotations is a library that simplifies caching in Spring based application using popular Ehcache library. In this article, I will present a simple way to integrate Ehcache in a spring based project.

Spring annotations are particularly useful when there is a need to cache methods of an application with minimal code changes and to use configuration to control the cache settings. In such cases, Ehcache Annotations can be used to dynamically configure caching of method return values.

For example, suppose you have a method: Product getProduct(long productId).

Once caching is added to this method, all calls to the method will be cached using the " productId" parameter as a key.

The steps described below works with Spring 3.1.0, Ehcache 2.5.1 and Ehcache-spring-annotations 1.2.0.

Step 1.

Configure maven to include the required libraries.

<dependency>
 <groupid>net.sf.ehcache</groupid>
 <artifactid>ehcache</artifactid>
 <version>2.5.1</version>
 <type>pom</type>
</dependency>
<dependency>
 <groupid>com.googlecode.ehcache-spring-annotations</groupid>
 <artifactid>ehcache-spring-annotations</artifactid>
 <version>1.2.0</version>
 <type>jar</type>
 <scope>compile</scope>
 <exclusions>
  <exclusion>
   <groupid>org.springframework</groupid>
   <artifactid>spring-expression</artifactid>
  </exclusion>
 </exclusions>
</dependency>
<!-- Include all spring dependencies -->
<dependency>
 <groupid>org.springframework</groupid>
 <artifactid>spring-core</artifactid>
 <version>3.1.0.RELEASE</version>
 <type>jar</type>
 <scope>compile</scope>
</dependency>

Step 2.

Configure Spring. You must add the following to your Spring configuration file in the beans declaration section:

<!-- Ehcache annotation config -->
<ehcache:annotation-driven cache-manager="ehCacheManager"/>

<bean id="ehCacheManager" class="org.springframework.cache.ehcache.EhCacheManagerFactoryBean">
 <property name="configLocation">
  <value>/WEB-INF/ehcache.xml</value>
 </property>
</bean>

Step 3.

Configure ehcache.xml and put it in /WEB-INF/ or in classpath.

<?xml version="1.0" encoding="UTF-8"?>
<ehcache xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:noNamespaceSchemaLocation="http://ehcache.org/ehcache.xsd" updateCheck="false">

    <defaultCache eternal="false" maxElementsInMemory="1000"
        overflowToDisk="false" diskPersistent="false" timeToIdleSeconds="0"
        timeToLiveSeconds="600" memoryStoreEvictionPolicy="LRU"/>

    <cache name="product" eternal="false"
        maxElementsInMemory="100" overflowToDisk="false" diskPersistent="false"
        timeToIdleSeconds="0" timeToLiveSeconds="300"
        memoryStoreEvictionPolicy="LRU" />

</ehcache>

 If you are not familiar with configuring EhCache please read their configuration guide.

Step 4.

Add the Annotation to methods you would like to cache. Lets assume you are using the Product getProduct(long productId) method from above.

@Cacheable(cacheName = "product")
public List getProduct(long productId) {
 Query query = entityManager.createQuery(" from Product where productId = :productId");
        query.setParameter("productId", productId);
 query.setMaxResults(10);
 return query.getResultList();
}

@Cacheable annotation can be placed on a method of an interface, or a public method on a class.

Note: The cache name should match the cache name defined in ehcache.xml. Multiple cache names can be defined in ehcache.xml.

What is Spring annotations library doing in the background?

EhCacheInterceptor.java is where all the work is done. It handles invocations on methods annotated with @Cacheable. It simply calls the method and stores the value in Ehcache if the key is not already present.

//See if there is a cached result
final Element element = cache.getWithLoader(cacheKey, null, methodInvocation);
if (element != null) {
    final Object value = element.getObjectValue();

    final boolean ignoreValue = cacheInterceptor.preInvokeCachable(cache, methodInvocation, cacheKey, value);
    if (!ignoreValue) {
 return value;
    }
}
....
....
//No cached value or exception, proceed
final Object value;
try {
    value = methodInvocation.proceed();
}
if ((value != null || cacheableAttribute.isCacheNull()) && shouldCache) {
     cache.put(new Element(cacheKey, value));
}

return value;

Simple, isn't it!