FactoryBeans and the annotation-based configuration in Spring 3.0

Question

Spring provides the FactoryBean interface to allow non-trivial initialisation of beans. The framework provides many implementations of factory beans and -- when using Spring's XML config -- factory beans are easy to use.

However, in Spring 3.0, I can't find a satisfactory way of using factory beans with the annotation-based configuration (née JavaConfig).

Obviously, I could manually instantiate the factory bean and set any required properties myself, like so:

@Configuration public class AppConfig {  ...      @Bean     public SqlSessionFactory sqlSessionFactory() throws Exception {         SqlSessionFactoryBean factory = new SqlSessionFactoryBean();         factory.setDataSource(dataSource());         factory.setAnotherProperty(anotherProperty());          return factory.getObject();     } 

However, this would fail if the FactoryBean implemented any Spring-specific callback interfaces, like InitializingBean, ApplicationContextAware, BeanClassLoaderAware, or @PostConstruct for example. I also need to inspect the FactoryBean, find out what callback interfaces it implements, then implement this functionality myself by calling setApplicationContext, afterPropertiesSet() etc.

This feels awkward and back-to-front to me: application-developers should not have to implement the callbacks of the IOC container.

Does anyone know of a better solution to using FactoryBeans from Spring Annotation configs?

Answer 1

I think that this is best solved when you rely on auto-wiring. If you are using Java configuration for the beans, this would like:

@Bean MyFactoryBean myFactory() {      // this is a spring FactoryBean for MyBean     // i.e. something that implements FactoryBean<MyBean>     return new MyFactoryBean(); }  @Bean MyOtherBean myOther(final MyBean myBean) {     return new MyOtherBean(myBean); } 

So Spring will inject for us the MyBean instance returned by the myFactory().getObject() as it does with XML configuration.

This should also work if you are using @Inject/@Autowire in your @Component/@Service etc classes.

Answer 2

As far as I understand your problem is what you want a result of sqlSessionFactory() to be a SqlSessionFactory (for use in other methods), but you have to return SqlSessionFactoryBean from a @Bean-annotated method in order to trigger Spring callbacks.

It can be solved with the following workaround:

@Configuration  public class AppConfig {      @Bean(name = "sqlSessionFactory")     public SqlSessionFactoryBean sqlSessionFactoryBean() { ... }      // FactoryBean is hidden behind this method     public SqlSessionFactory sqlSessionFactory() {         try {             return sqlSessionFactoryBean().getObject();         } catch (Exception ex) {             throw new RuntimeException(ex);         }     }      @Bean     public AnotherBean anotherBean() {         return new AnotherBean(sqlSessionFactory());     } } 

The point is that calls to @Bean-annotated methods are intercepted by an aspect which performs initialization of the beans being returned (FactoryBean in your case), so that call to sqlSessionFactoryBean() in sqlSessionFactory() returns a fully initialized FactoryBean.