深入理解Spring原始碼之自動裝配
自動裝配;
Spring利用依賴注入(DI),完成對IOC容器中中各個元件的依賴關係賦值;
1)、@Autowired:自動注入:
1)、預設優先按照型別去容器中找對應的元件:applicationContext.getBean(BookDao.class);找到就賦值
2)、如果找到多個相同型別的元件,再將屬性的名稱作為元件的id去容器中查詢
applicationContext.getBean("bookDao")
3)、@Qualifier("bookDao"):使用@Qualifier指定需要裝配的元件的id,而不是使用屬性名
4)、自動裝配預設一定要將屬性賦值好,沒有就會報錯;
可以使用@Autowired(required=false);
5)、@Primary:讓Spring進行自動裝配的時候,預設使用首選的bean;
也可以繼續使用@Qualifier指定需要裝配的bean的名字
BookService{
@Autowired
BookDao bookDao;
}
2)、Spring還支援使用@Resource(JSR250)和@Inject(JSR330)[java規範的註解]
@Resource:
可以和@Autowired一樣實現自動裝配功能;預設是按照元件名稱進行裝配的;
沒有能支援@Primary功能沒有支援@Autowired(reqiured=false);
@Inject:
需要匯入javax.inject的包,和Autowired的功能一樣。沒有required=false的功能;
@Autowired:Spring定義的; @Resource、@Inject都是java規範
AutowiredAnnotationBeanPostProcessor:解析完成自動裝配功能;
3)、 @Autowired:構造器,引數,方法,屬性;都是從容器中獲取引數元件的值
1)、[標註在方法位置]:@Bean+方法引數;引數從容器中獲取;預設不寫@Autowired效果是一樣的;都能自動裝配
2)、[標在構造器上]:如果元件只有一個有參構造器,這個有參構造器的@Autowired可以省略,引數位置的元件還是可以自動從容器中獲取
3)、放在引數位置:
4)、自定義元件想要使用Spring容器底層的一些元件(ApplicationContext,BeanFactory,xxx);
自定義元件實現xxxAware;在建立物件的時候,會呼叫介面規定的方法注入相關元件;Aware;
把Spring底層一些元件注入到自定義的Bean中;
xxxAware:功能使用xxxProcessor;
ApplicationContextAware==》ApplicationContextAwareProcessor;
舉例檢視ApplicationContextAware的完整初始化過程:
public class IOCTest_Autowired {
@Test
public void test01(){
AnnotationConfigApplicationContext applicationContext = new
AnnotationConfigApplicationContext(MainConifgOfAutowired.class);
}
}
package com.atguigu.bean; import org.springframework.beans.BeansException; import org.springframework.beans.factory.BeanNameAware; import org.springframework.context.ApplicationContext; import org.springframework.context.ApplicationContextAware; import org.springframework.context.EmbeddedValueResolverAware; import org.springframework.stereotype.Component; import org.springframework.util.StringValueResolver; @Component public class AwareBean implements ApplicationContextAware,BeanNameAware,EmbeddedValueResolverAware { private ApplicationContext applicationContext; @Override public void setApplicationContext(ApplicationContext applicationContext) throws BeansException { // TODO Auto-generated method stub System.out.println("傳入的ioc:"+applicationContext); this.applicationContext = applicationContext; } @Override public void setBeanName(String name) { // TODO Auto-generated method stub System.out.println("當前bean的名字:"+name); } @Override public void setEmbeddedValueResolver(StringValueResolver resolver) { // TODO Auto-generated method stub String resolveStringValue = resolver.resolveStringValue("你好 ${os.name} 我是 #{20*18}"); System.out.println("解析的字串:"+resolveStringValue); } }
斷點檢視呼叫棧如下:
-->AnnotationConfigApplicationContext refresh(); -->finishBeanFactoryInitialization(beanFactory); -->beanFactory.preInstantiateSingletons() -->DefaultListableBeanFactory getBean(beanName) -->AbstractBeanFactory doGetBean(name, null, null, false); -->AbstractBeanFactory getSingleton(beanName, new ObjectFactory<Object>() --> DefaultSingletonBeanRegistry singletonFactory.getObject() -->AbstractBeanFactory createBean(beanName, mbd, args) -->AbstractAutowireCapableBeanFactory doCreateBean(beanName, mbdToUse, args) -->AbstractAutowireCapableBeanFactory initializeBean(beanName, exposedObject, mbd) -->AbstractAutowireCapableBeanFactory applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName) -->AbstractAutowireCapableBeanFactory beanProcessor.postProcessBeforeInitialization(result, beanName); -->ApplicationContextAwareProcessor invokeAwareInterfaces(bean); -->ApplicationContextAwareProcessor ((ApplicationContextAware) bean).setApplicationContext(this.applicationContext); -->AwareBean setApplicationContext
開啟ApplicationContextAwareProcessor的原始碼發現它實現了BeanPostProcessor前置類在postProcessBeforeInitialization方法裡呼叫invokeAwareInterfaces最後一步時設定spring容器
private void invokeAwareInterfaces(Object bean) {
if (bean instanceof Aware) {
if (bean instanceof EnvironmentAware) {
((EnvironmentAware) bean).setEnvironment(this.applicationContext.getEnvironment());
}
if (bean instanceof EmbeddedValueResolverAware) {
((EmbeddedValueResolverAware) bean).setEmbeddedValueResolver(this.embeddedValueResolver);
}
if (bean instanceof ResourceLoaderAware) {
((ResourceLoaderAware) bean).setResourceLoader(this.applicationContext);
}
if (bean instanceof ApplicationEventPublisherAware) {
((ApplicationEventPublisherAware) bean).setApplicationEventPublisher(this.applicationContext);
}
if (bean instanceof MessageSourceAware) {
((MessageSourceAware) bean).setMessageSource(this.applicationContext);
}
if (bean instanceof ApplicationContextAware) {
((ApplicationContextAware) bean).setApplicationContext(this.applicationContext);
}
}
}