Spring Beans and dependency injection

Spring Beans and dependency injection

1. @ComponentScan is used to find your beans,

   • @Component, @Service, @Repository, @Controller etc
     • And if a bean has one constructor, you can omit the @Autowired.
   • @SpringBootApplication
     • Is the composite of @Configuration, @ComponentScan, and @EnableAutoConfiguration
   • <context:component-scan base-package="com.example.foo, com.example.bar"/>

2. One type of DI is constructor injection (On a constructor method)

   • <bean id="knight" class="com.springinaction.knights.BraveKnight"> <constructor-arg ref="quest" /> </bean>
     • <bean id="quest" class="com.springinaction.knights.SlayDragonQuest"> <constructor-arg value="#{T(System).out}" /> </bean>
     • To use a shortchut p:nameAttribute. You need to set in your XML header xmlns:p="http://www.springframework.org/schema/p"
   • @Autowired Public Knight(Quest quest) { ... }
     • @Configuration public class KnightConfig { @Bean public Knight knight() { return new BraveKnight(quest()); } @Bean public Quest quest() { return new SlayDragonQuest(System.out); } }
       • A bean can have multiples names
         • @Bean(name = { "value1", "value2" } )

3. public interface CompactDisc { void play(); }

   • @Component public class SgtPeppers implements CompactDisc { private String title = "Sgt. Pepper's Lonely Hearts Club Band"; private String artist = "The Beatles"; public void play() { System.out.println("Playing " + title + " by " + artist); } }

4. If there are two implementations of a bean. Spring will throw a NoUniqueBeanDefinitionException

   • Autowirin with @Qualifier("NomeDoBean")
     • Or you can use @Primary anottation
     • you can create a custom Qualifier, creating a Annotation with the @Qualifier annotation within
       • @Qualifier public @interface Genre { String value(); }
         • @Autowired @Genre("Action") private MovieCatalog actionCatalog;
           • <bean class="br.com.Exemplo"><qualifier type="Genre" value="Action"/></bean>
       • @Autowired @MovieQualifier(format=Format.DVD, genre="Action") private MovieCatalog actionDvdCatalog;
         • <bean class="br.com.Exemplo"> <qualifier type="MovieQualifier"> <attribute key="format" value="VHS"/> <attribute key="genre" value="Action"/> </qualifier> </bean>
           • Type is the type of annotation. Relative or qualified
           • Attribute tag with key and value for distinction the qualifier (inner qualifier)
           • XML can validate a unique id for bean
         • <bean class="example.SimpleMovieCatalog"><meta key="format" value="DVD"/><metakey="genre" value="Action"/></bean>
           • Meta tag with key and value for distinction the qualifier
     • <bean class="br.com.Exemplo"> <qualifier value="NomeDoBean"/> </bean>
     • can be used on properties, setters, and constructors.
     • JSR 330's @Qualifier or Spring @Qualifier
   • Or spring use the field name to determine what bean should use

5. ApplicationContext (Interface)

   • enhances BeanFactory
   • Bean instantiation/wiring
   • Automatic BeanPostProcessor registration
   • Automatic BeanFactoryPostProcessor registration
   • MessageSource (i18n)
   • ApplicationEvent publication
   • AnnotationConfigApplicationContext
     • AnnotationConfigWebApplicationContext
     • new AnnotationConfigApplicationContext( com.springinaction.knights.config.KnightConfig.class);
   • ClassPathXmlApplicationContext
     • new ClassPathXmlApplicationContext("knight.xml");
       • <beans> <import resources="myServices.xml"/> <import resources="myResources/messageSourceA.xml"/> <import resources="/myResources/messageSourceB.xml"/> </beans>
   • FileSystemXmlApplicationContext
     • new FileSystemXmlApplicationContext("c:/knight.xml");
   • XmlWebApplicationContext
   • WebApplicationContext
     • ContextLoaderListener
       • Bootstrap listener to start up and shut down Spring's root WebApplicationContext.

6. BeanFactory (Interface)

   • Bean instantiation/wiring

7. Bean Life Cycle

   • Instantiate
     • Populate properties
       • BeanNameAware’s setBeanName()
         • BeanFactoryAware’s setBeanFactory()
           • ApplicationContextAware’s setApplicationContext()
             • Pre-initialization BeanPostProcessors
               • InitializingBean ’s afterPropertiesSet
                 • Call custom init-method
                   • Post-initialization BeanPostProcessors
                     • BEAN IS READY TO USE
                       • @PostConstruct and @PreDestroy
                         • Methods can have any access modifier, but no arguments and return void
                         • Defined by JSR-250
                         • Also used by EJB3
                         • Alternative in @Configuration is @Bean(initMethod="init”, destroyMethod="destroy") - can be used for third party beans
                         • Method is invoked by Spring after DI (PostConstruct)
                           • equivalent to init-method attribute
                         • @PreDestroy
                           • Method is invoked before bean is destroyed
                           • Is not called for prototype scoped beans!
                           • After application context is closed
                           • Only if JVM exits normally
                           • equivalent to destroy-method attribute
                   • If the bean implements BeanPostProcessor,
                     • postProcessAfterInitialization()
                 • If the bean implements the InitializingBean interface
                   • afterPropertiesSet()
               • If the bean implements the BeanPostProcessor interface,
                 • postProcessBeforeInitialization()
             • If the bean implements ApplicationContextAware
           • If the bean implements BeanFactoryAware
         • If the bean implements BeanNameAware
           • setBeanName()
   • Constructor method is called before DI

8. Container shutdown

   • DisposableBean’s destroy()
     • Call custom destroy-method
       • End of bean
     • If the bean implements the DisposableBean interface
       • destroy()
   • registerShutdownHook()
     • shutdown and call the relevant destroy methods
     • Method of AbstractApplicationContext

9. @Autowired

   • Field, Constructor or methods
   • @Resource
     • Identifies dependencies for injection by name, not by type like @Autowired
       • Name is spring bean name
     • Can be used for field and setter DI, not for constructors
       • With name @Resource("beanName") or without
   • @Required ou required= true
   • when using in constructor
     • only one can have required=true