自动装配;
Spring利用依赖注入(DI),完成对IOC容器中中各个组件的依赖关系赋值;
1)、@Autowired:自动注入:
1)、默认优先按照类型去容器中找对应的组件:applicationContext.getBean(BookDao.class);找到就赋值
2)、如果找到多个相同类型的组件,再将属性的名称作为组件的id去容器中查找
applicationContext.getBean("bookDao")
3)、@Qualifier("bookDao"):使用@Qualifier指定需要装配的组件的id,而不是使用属性名
4)、自动装配默认一定要将属性赋值好,没有就会报错;
可以使用@Autowired(required=false);
5)、@Primary:让Spring进行自动装配的时候,默认使用首选的bean;
也可以继续使用@Qualifier指定需要装配的bean的名字
BookService{
@Autowired
BookDao bookDao;
}
2)、Spring还支持使用@Resource(JSR250)和@Inject(JSR330)[java规范的注解]
@Resource:
可以和@Autowired一样实现自动装配功能;默认是按照组件名称进行装配的;
没有能支持@Primary功能没有支持@Autowired(reqiured=false);
@Inject:
需要导入javax.inject的包,和Autowired的功能一样。没有required=false的功能;
@Autowired:Spring定义的; @Resource、@Inject都是java规范
AutowiredAnnotationBeanPostProcessor:解析完成自动装配功能;
3)、 @Autowired:构造器,参数,方法,属性;都是从容器中获取参数组件的值
1)、[标注在方法位置]:@Bean+方法参数;参数从容器中获取;默认不写@Autowired效果是一样的;都能自动装配
2)、[标在构造器上]:如果组件只有一个有参构造器,这个有参构造器的@Autowired可以省略,参数位置的组件还是可以自动从容器中获取
3)、放在参数位置:
4)、自定义组件想要使用Spring容器底层的一些组件(ApplicationContext,BeanFactory,xxx);
自定义组件实现xxxAware;在创建对象的时候,会调用接口规定的方法注入相关组件;Aware;
把Spring底层一些组件注入到自定义的Bean中;
xxxAware:功能使用xxxProcessor;
ApplicationContextAware==》ApplicationContextAwareProcessor;
举例查看ApplicationContextAware的完整初始化过程:
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("传入的ioc:"+applicationContext);
this.applicationContext = applicationContext;
}
@Override
public void setBeanName(String name) {
// TODO Auto-generated method stub
System.out.println("当前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("解析的字符串:"+resolveStringValue);
}
}
断点查看调用栈如下:
-->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
打开ApplicationContextAwareProcessor的源码发现它实现了BeanPostProcessor前置类在postProcessBeforeInitialization方法里调用invokeAwareInterfaces最后一步时设置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);
}
}
}