02.Spring Framework 之 Bean 生命週期回調

1. Bean 的生命週期回調

單實例 bean 對象：在容器啓動的時候創建對象，在容器關閉的時候銷燬對象

多實例 bean 對象：在每次獲取的時候創建對象，容器不會調用銷燬方法

2. 初始化和銷燬方法

代碼已經上傳至 https://github.com/masteryourself-tutorial/tutorial-spring ，詳見 tutorial-spring-framework/tutorial-spring-framework-lifecycle 工程

2.1 @Bean 實現

1. Student

public class Student {

	public Student() {
		System.out.println("student constructor");
	}

	public void initMethod() {
		System.out.println("student initMethod");
	}

	public void destroyMethod() {
		System.out.println("student destroyMethod");
	}

}

2. SpringConfig

@Configuration
@Import(ExtBeanPostProcessor.class)
public class SpringConfig {

	@Bean(initMethod = "initMethod", destroyMethod = "destroyMethod")
	public Student student() {
		return new Student();
	}

	@Bean
	public Teacher teacher() {
		return new Teacher();
	}

	@Bean
	public Principal principal() {
		return new Principal();
	}

}

2.2 InitializingBean & DisposableBean 接口

1. Teacher

public class Teacher implements InitializingBean, DisposableBean {

	public Teacher() {
		System.out.println("teacher constructor");
	}

	@Override
	public void afterPropertiesSet() throws Exception {
		System.out.println("teacher afterPropertiesSet");
	}

	@Override
	public void destroy() throws Exception {
		System.out.println("teacher destroy");
	}

}

2.3 @PostConstruct & @PreDestroy 註解

1. Principal

public class Principal {

	public Principal() {
		System.out.println("principal constructor");
	}

	@PostConstruct
	public void postConstruct() {
		System.out.println("principal postConstruct");
	}

	@PreDestroy
	public void preDestroy() {
		System.out.println("principal preDestroy");
	}

}

2.4 BeanPostProcessor

1. ExtBeanPostProcessor

public class ExtBeanPostProcessor implements BeanPostProcessor {

	@Override
	public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
		if (bean instanceof Student || bean instanceof Teacher || bean instanceof Principal) {
			System.out.println(String.format("%s =================>>>>>>>>>>>>> postProcessBeforeInitialization", beanName));
		}
		return bean;
	}

	@Override
	public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
		if (bean instanceof Student || bean instanceof Teacher || bean instanceof Principal) {
			System.out.println(String.format("%s =================>>>>>>>>>>>>> postProcessAfterInitialization", beanName));
		}
		return bean;
	}

}