Introduction

Dependency Injection Advanced

Topics

• Dependency Injection (DI)
  • Bean Life Cycle Management
  • ApplicationContext

Bean Life Cycle Management

• beans can be constructed on a way that they receive notifications at certain points in their life cycles
• enables your beans to perform relevant processing at certain points throughout their lives
• two life cycle events
  • postinitialization
  • predestruction

Bean Life Cycle Management

• postinitialization
  • after setting property values and after finising dependency checks
• predestruction
  • before Spring destroys the bean instance
• works only with singletons

PostInitialization

• specifying an Initialization Method

public class InitDestroyBean {
	...	
	public void init(){	... }	
	...
	
   // <bean id="initDestroyBean" class="...InitDestroyBean" 
   //          init-method="init" destroy-method="destroy">
   //    ...
   // </bean>
}

PostInitialization

• executing a Method When a Bean Is Destroyed

public class InitDestroyBean {
	...
	public void destroy(){ ... 	}
	
   // <bean id="initDestroyBean" class="...InitDestroyBean" 
   //           init-method="init" destroy-method="destroy">
   //    ...
   // </bean>
}

PostInitialization

• implementing InitializingBean Interface

public class InitializingDisposableBean implements InitializingBean {
	...
	public void afterPropertiesSet(){ ... 	}
	
   // <bean id="initializingDisposableBean" 
   //       class="...InitializingDisposableBean"> 
   //  ...
   // </bean>
}

PostInitialization

• implementing DisposableBean Interface

public class InitializingDisposableBean implements DisposableBean {
	...
	public void destroy(){ ... 	}
	
   // <bean id="initializingDisposableBean" 
   //       class="...initializingDisposableBean">
   //    ...
   // </bean>
}

Spring Aware Beans

• BeanNameAware makes the object aware of its bean name

public class BeanNameAwareBean implements BeanNameAware {
	...
	public void setBeanName(){ ... 	}
	
   // <bean id="beanNameAwareBean" 
   //       class="...BeanNameAwareBean">
   // </bean>
}

Spring Aware Beans

• BeanFactoryAware gives the bean access to the BeanFactory that created the bean

public class BeanFactoryAwareBean 
             implements BeanFactoryAware {
	...
	public void setBeanFactory(){ ... 	}
	
   // <bean id="beanFactoryAwareBean" 
   //       class="...BeanFactoryAwareBean">
   // </bean>
}

Beans Factory Post Processing

• provides a way for applications to modify their Spring context�s bean definitions before any beans get created

public class BeanFactoryPostProcessorBean 
             implements BeanFactoryPostProcessor {
	...
	public void postProcessBeanFactory(...){ ... 	}
	
   // <bean id="beanFactoryPostProcessorBean" 
   //       class="...BeanFactoryPostProcessorBean">
   // </bean>
}

Beans Post Processor

• perform additional processing immediately before and after Spring instantiates the bean

public class MyBeanPostProcessor 
             implements BeanPostProcessor {
	...
	public Object postProcessBeforeInitialization(...){ ... }
	
	public Object postProcessAfterInitialization(...){ ... }
	
   // <bean id="myBeanPostProcessor" 
   //       class="...MyBeanPostProcessor">
   // </bean>
}

Application Context

• extension of the BeanFactory interface
• enables enterprise-specific features such as transactions and AOP
• providing extra features over BeanFactory

Application Context

• features over BeanFactory
  • additional life-cycle interfaces
  • event propagation to beans implementing the ApplicationListener interface
  • MessageSource, providing access to messages in, i18n-style
  • access to resources, such as URLs and files
  • loading of multiple (hierarchical) contexts

Application Context

• when to use
  • always use ApplicationContext over BeanFactory to take advantage of its extended functionality
  • except for a few limited situations such as perhaps in an Applet, where memory consumption might be critical

Application Context

• Usage
  • ApplicationContext can be used in a declarative fashion(e.g. ContextLoader in J2EE webapp)
  • can be created programmatically as well

...
ApplicationContext applicationContext = new ClassPathXmlApplicationContext("applicationcontextaware-context.xml");
...