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:

 package org.bk.samples.cache;
 
 import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.equalTo;
 
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Random;
 
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.cache.Cache;
 import org.springframework.cache.annotation.Cacheable;
 import org.springframework.cache.annotation.EnableCaching;
 import org.springframework.cache.concurrent.ConcurrentMapCacheFactoryBean;
 import org.springframework.cache.support.SimpleCacheManager;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.ComponentScan;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.stereotype.Component;
 import org.springframework.test.context.ContextConfiguration;
 import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
 
 @RunWith(SpringJUnit4ClassRunner.class)
 @ContextConfiguration(classes={TestSpringCache.TestConfiguration.class})
 public class TestSpringCache {
 
  @Autowired TestService testService;
 
  @Test
  public void testCache() {
   String response1 = testService.cachedMethod('param1', 'param2');
   String response2 = testService.cachedMethod('param1', 'param2');
   assertThat(response2, equalTo(response1));
  }
 
 
  @Configuration
  @EnableCaching
  @ComponentScan('org.bk.samples.cache')
  public static class TestConfiguration{
 
   @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;
   }
  }
 
 }
 
 interface TestService{
  String cachedMethod(String param1,String param2);
 }
 
 @Component
 class TestServiceImpl implements TestService{
 
  @Cacheable(value='default', key='#p0.concat('-').concat(#p1)')
  public String cachedMethod(String param1, String param2){
   return 'response ' + new Random().nextInt();
  }
 }
 

Reference: Spring @Configuration and FactoryBean from our JCG partner Biju Kunjummen at the all and sundry blog.