ApplicationContextAware和BeanFactoryAware使用理解

1.Spring容器会自动把上下文环境对象调用ApplicationContextAware接口中的setApplicationContext方法；当一个类实现了这个接口之后，这个类就可以非常方便的获取到ApplicationContext中的所有的bean；简而言之，言而总之，此类可以获取到spring配置文件中所有的bean对象。

2.基本原理见如下代码，核心类：ApplicationContextAwareProcessor

public Object postProcessBeforeInitialization(final Object bean, String beanName) throws BeansException {
    AccessControlContext acc = null;
 
    if (System.getSecurityManager() != null &&
            (bean instanceof EnvironmentAware || bean instanceof EmbeddedValueResolverAware ||    bean instanceof ResourceLoaderAware || bean instanceof ApplicationEventPublisherAware ||    bean instanceof MessageSourceAware || bean instanceof ApplicationContextAware)) {
            acc = this.applicationContext.getBeanFactory().getAccessControlContext();
    }
 
    if (acc != null) {
        AccessController.doPrivileged(new PrivilegedAction<Object>() {
            public Object run() {
                invokeAwareInterfaces(bean);
                return null;
            }
        }, acc);
    }
    else {
        invokeAwareInterfaces(bean);
    }
 
    return bean;
}
 
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(
                new EmbeddedValueResolver(this.applicationContext.getBeanFactory()));
        }
        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);
        }
    }
}

在启动Spring容器创建bean的时候会执行postProcessBeforeInitialization这个方法，发现实现了Aware接口的类（例如最后一个ApplicationContextAware），都会加载spring的applicationContext。

3.代码实例讲解（此处讲解通过实现BeanFactoryAware接口将bean注册到beanfactory中）：
首先通过实现BeanFactoryAware接口将bean注册到spring容器中。

@Component
public class BeanFactoryHelper implements BeanFactoryAware {
 
    private static BeanFactory beanFactory;
 
    @Override
    public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
        this.beanFactory = beanFactory;
    }
 
    public static BeanFactory getBeanFactory() {
        return this.beanFactory;
    }
}
 
//获取beanFactory并注册到spring上下文中
DefaultListableBeanFactory beanFactory = (DefaultListableBeanFactory) BeanFactoryHolder.getBeanFactory();
 
String beanName = "test";
beanFactory.destroySingleton(beanName);
 
beanFactory.registerSingleton(beanName, singletonObject);

注册到spring上下文之后就可以通过实现ApplicationContextAware接口来获取bean对象：

@Component
public class ApplicationContextHelper implements ApplicationContextAware {
    private static ApplicationContext ctx;
 
    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        this.ctx = applicationContext;
    }
 
    public static ApplicationContext getApplicationContext() {
        return this.ctx;
    }
 
    public static Object getBean(String beanName) {
        return this.ctx.getBean(beanName);
    }
 
    public static <T> T getBean(Class<T> clazz) {
        return this.ctx.getBean(clazz);
    }
 
    public static <T> T getBean(String beanName, Class<T> clazz) {
        try {
            return this.ctx.getBean(beanName, clazz);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }
}

上面两种方法，只有容器启动的时候，才会把BeanFactory和ApplicationContext注入到自定义的helper类中，如果在本地junit测试的时候，如果需要根据bean的名称获取bean对象，则可以通过ClassPathXmlApplicationContext来获取一个ApplicationContext，代码如下：

@Test
    public void test() throws SQLException {
        //通过从classpath中加载spring-mybatis.xml实现bean的获取
        ApplicationContext context = new ClassPathXmlApplicationContext("spring-mybatis.xml");
        IUserService userService = (IUserService) context.getBean("userService");

        User user = new User();
        user.setName("test");
        user.setAge(20);
        userService.addUser(user);
    }

本文转自：https://blog.csdn.net/jianjun200607/article/details/94986347

https://www.cnblogs.com/handsomeye/p/6277510.html