Spring底层原理(三)
Bean的生命周期
@SpringBootApplication
public class Application {
public static void main(String[] args) {
ConfigurableApplicationContext context = SpringApplication.run(Application.class, args);
context.close();
}
}
@Slf4j
@Component
public class LifeCycleBean {
public LifeCycleBean(){
log.info("构造");
}
@Autowired
public void autowire(@Value("${JAVA_HOME}") String home){
log.info("依赖注入:{}",home);
}
@PostConstruct
public void init(){
log.info("初始化");
}
@PreDestroy
public void destroy(){
log.info("销毁");
}
}
启动容器后会得到以下结果
Bean的生命周期为:构造方法 -> 依赖注入->初始化 ->销毁
与Bean生命周期相关的后置处理器
PostProcessor中文意思为后置处理器
InstantiationAwareBeanPostProcessor与DestructionAwareBeanPostProcessor都是BeanPostProcessor的子接口
@Slf4j
@Component
public class MyBeanPostProcessor implements InstantiationAwareBeanPostProcessor, DestructionAwareBeanPostProcessor {
@Override
public void postProcessBeforeDestruction(Object bean, String beanName) throws BeansException {
if (beanName.equals("lifeCycleBean")){
log.info("<<<< 销毁前执行，如@PreDestory");
}
}
@Override
public Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException {
if (beanName.equals("lifeCycleBean")){
log.debug("<<<< 实例化之前执行，这里返回的对象会替换掉原本的bean");
}
return null;
}
@Override
public boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException {
if (beanName.equals("lifeCycleBean")){
log.debug("<<<< 实例化后执行，这里返回false会跳过依赖注入阶段");
}
return true;
}
@Override
public PropertyValues postProcessProperties(PropertyValues pvs, Object bean, String beanName) throws BeansException {
if (beanName.equals("lifeCycleBean")){
log.debug("<<<< 依赖注入阶段执行，如@Autowired、@Value、@Resource");
}
return pvs;
}
@Override
public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
if (beanName.equals("lifeCycleBean")){
log.debug("<<<< 初始化之前执行，这里返回的对象会替换掉原本的bean,如@PostConstruct、@ConfigurationProperties");
}
return bean;
}
@Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
if (beanName.equals("lifeCycleBean")){
log.debug("<<<< 初始化之后执行，这里返回的对象会替换掉原本的bean,如代理增强");
}
return bean;
}
}
Bean后置处理器与模板方法模式
public class MethodTemplateTest {
public static void main(String[] args) {
MyBeanFactory factory = new MyBeanFactory();
factory.addProcessor(bean -> System.out.println("解析@Autowired"));
factory.addProcessor(bean -> System.out.println("解析@Resources"));
factory.getBean();
}
static class MyBeanFactory {
private List<BeanPostProcessor> processors = new ArrayList<>();
public void addProcessor(BeanPostProcessor postProcessor) {
processors.add(postProcessor);
}
public Object getBean() {
Object bean = new Object();
System.out.println("构造:" + bean);
System.out.println("依赖注入:" + bean);
for (BeanPostProcessor processor : processors) {
processor.inject(bean);
}
System.out.println("初始化:" + bean);
return bean;
}
}
interface BeanPostProcessor {
void inject(Object bean);//对依赖注入阶段进行拓展
}
}
-
将代码中不确定的部分抽象成接口，供后续拓展
常见的bean后置处理器
public class A4Application {
public static void main(String[] args) {
//GenericApplicationContext是一个干净的容器，没有添加BeanFactory后置处理器和Bean后置处理器
GenericApplicationContext context = new GenericApplicationContext();
//注册bean
context.registerBean("bean1",Bean1.class);
context.registerBean("bean2",Bean2.class);
context.registerBean("bean3",Bean3.class);
//初始化容器
context.refresh();//执行beanFactory后置处理器，添加bean后置处理器,初始化所有单例bean
//销毁容器
context.close();
}
}
添加AutowiredAnnotationBeanPostProcessor
context.getDefaultListableBeanFactory().setAutowireCandidateResolver(new ContextAnnotationAutowireCandidateResolver()); context.registerBean(AutowiredAnnotationBeanPostProcessor.class);
-
ContextAnnotationAutowireCandidateResolver:用于支持解析@Value -
AutowiredAnnotationBeanPostProcessor:该处理器用于解析@Autowired@Value
添加CommonAnnotationBeanPostProcessor
context.registerBean(CommonAnnotationBeanPostProcessor.class);
-
CommonAnnotationBeanPostProcessor:用于解析@Resurce@PostConstruct@PreDestroy
ConfigurationPropertiesBindingPostProcessor.register(context);
-
ConfigurationPropertiesBindingPostProcessor:用于解析@ConfigurationProperties
