Friday, August 10, 2012

Spring @Configuration and FactoryBean

Consider a FactoryBean  for defining a cache using a Spring configuration file:

 <cache:annotation-driven />
 <context:component-scan base-package="org.bk.samples.cachexml"></context:component-scan>
 
 <bean id="cacheManager" class="org.springframework.cache.support.SimpleCacheManager">
  <property name="caches">
   <set>
    <ref bean="defaultCache"/>
   </set>
  </property>
 </bean>
 
 <bean name="defaultCache" class="org.springframework.cache.concurrent.ConcurrentMapCacheFactoryBean">
  <property name="name" value="default"/>
 </bean>

The factory bean ConcurrentMapCacheFactoryBean is a bean which is in turn responsible for creating a Cache bean.

My first attempt at translating this setup to a @Configuration style was the following:


@Bean
public SimpleCacheManager cacheManager(){
 SimpleCacheManager cacheManager = new SimpleCacheManager();
 List<Cache> caches = new ArrayList<Cache>();
 ConcurrentMapCacheFactoryBean cacheFactoryBean = new ConcurrentMapCacheFactoryBean();
 cacheFactoryBean.setName("default");
 caches.add(cacheFactoryBean.getObject());
 cacheManager.setCaches(caches );
 return cacheManager;
}

This did not work however, the reason is that here I have bypassed some Spring bean lifecycle mechanisms altogether. It turns out that ConcurrentMapCacheFactoryBean also implements the InitializingBean interface and does a eager initialization of the cache in the "afterPropertiesSet" method of InitializingBean. Now by directly calling factoryBean.getObject() , I was completely bypassing the afterPropertiesSet method.

There are two possible solutions:
1. Define the FactoryBean the same way it is defined in the XML:
@Bean
public SimpleCacheManager cacheManager(){
 SimpleCacheManager cacheManager = new SimpleCacheManager();
 List<Cache> caches = new ArrayList<Cache>();
 caches.add(cacheBean().getObject());
 cacheManager.setCaches(caches );
 return cacheManager;
}

@Bean
public ConcurrentMapCacheFactoryBean cacheBean(){
 ConcurrentMapCacheFactoryBean cacheFactoryBean = new ConcurrentMapCacheFactoryBean();
 cacheFactoryBean.setName("default");
 return cacheFactoryBean;
}
In this case, there is an explicit FactoryBean being returned from a @Bean method, and Spring will take care of calling the lifecycle methods on this bean.

2. Replicate the behavior in the relevant lifecycle methods, in this specific instance I know that the FactoryBean instantiates the ConcurrentMapCache in the afterPropertiesSet method, I can replicate this behavior directly this way:

@Bean
public SimpleCacheManager cacheManager(){
 SimpleCacheManager cacheManager = new SimpleCacheManager();
 List<Cache> caches = new ArrayList<Cache>();
 caches.add(cacheBean());
 cacheManager.setCaches(caches );
 return cacheManager;
}

@Bean
public Cache  cacheBean(){
 Cache  cache = new ConcurrentMapCache("default");
 return cache;
}

Something to keep in mind when translating a FactoryBean from xml to @Configuration.

Note:
A working one page test as a gist is available here:

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