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Spring的Aware接口实现及执行顺序详解

2022-12-26 12:01

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一、实现了Aware的接口

Spring中有很多继承于aware中的接口，这些接口到底是做什么用到的，下面我们就一起来看看吧。

Aware 接口用于注入一些与容器相关信息，例如：

EnvironmentAware：实现EnvironmentAware接口重写setEnvironment方法后，可以获得配置文件属性值

BeanClassLoaderAware：注入加载当前 bean 的 ClassLoader

BeanNameAware: 注入当前 bean 对应 beanName

BeanFactoryAware: 注入当前BeanFactory容器的引用

ApplicationContextAware: 获取容器本身ApplicationContext对象，可以在bean中得到bean所在的应用上下文

EmbeddedValueResolverAware：获取properties文件单个属性值，一般使用@Value属性值；EmbeddedValueResolverAware是另一种基于Spring解析获取 properties 文件单个属性值的方式

ApplicationEventPublisherAware：事件发布器的接口，使用这个接口，我们自己的bean就拥有了发布事件的能力。

ResourceLoaderAware：获取ResourceLoader实例，获取资源加载器读取资源文件

二、为什么要使用 Aware 接口

Aware接口是回调，监听器和观察者设计模式的混合，一般指具备由Spring 容器通过Aware回调方法通知的特定的bean对象，简单来说就是可以通过实现该接口拿到Spring容器内部的一些资源。实际的回调方法由各个子接口确定，通常应仅包含一个接受单个参数、返回 void 的方法；但是一般情况下，Spring不建议使用该接口，因为使用这种方式会将业务代码与Spring 耦合，有所违背IOC 原则。

1、BeanNameAware

public class MyBeanName implements BeanNameAware {
    @Override
    public void setBeanName(String beanName) {
        System.out.println(beanName);
    }
}

2、BeanFactoryAware

public class MyBeanFactory implements BeanFactoryAware {
    private BeanFactory beanFactory;
    @Override
    public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
        this.beanFactory = beanFactory;
    }
    public void getMyBeanName() {
        MyBeanName myBeanName = beanFactory.getBean(MyBeanName.class);
        System.out.println(beanFactory.isSingleton("myCustomBeanName"));
    }
}

3、EnvironmentAware

@Configuration
public class MyBatisConfig implements EnvironmentAware {
    private static Environment environment;
    @Override
    public void setEnvironment(Environment environment) {
        this.environment = environment;
    }
    @Bean
    public DataSource druidDataSource() throws Exception {
        Properties props = new Properties();
        props.put("driverClassName", environment.getProperty("datasource.driverClassName"));
        props.put("url", environment.getProperty("datasource.url"));
        props.put("username", environment.getProperty("datasource.username"));
        props.put("password", environment.getProperty("datasource.password"));
        return DruidDataSourceFactory.createDataSource(props);
    }
}

4、EmbeddedValueResolverAware

@Component
public class PropertiesUtil implements EmbeddedValueResolverAware {
    private StringValueResolver resolver;
    @Override
    public void setEmbeddedValueResolver(StringValueResolver resolver) {
        this.resolver = resolver;
    }
    
    public String getPropertiesValue(String key) {
        StringBuilder name = new StringBuilder("${").append(key).append("}");
        return resolver.resolveStringValue(name);
    }
}

public class MyBean implements BeanNameAware, ApplicationContextAware, InitializingBean {
    private static final Logger log = LoggerFactory.getLogger(MyBean.class);
    @Override
    public void setBeanName(String name) {
        log.debug("当前bean " + this + " 名字叫:" + name);
    }
    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        log.debug("当前bean " + this + " 容器是:" + applicationContext);
    }
    @Override
    public void afterPropertiesSet() throws Exception {
        log.debug("当前bean " + this + " 初始化");
    }
}

三、Aware接口执行顺序

定义类SimpleAware实现了部分Aware的接口的自定义bean，经过程序运行测试其执行顺序如下：

@Component
public class SimpleAware implements
        ApplicationContextAware,
        ApplicationEventPublisherAware,
        BeanClassLoaderAware,
        BeanFactoryAware,
        BeanNameAware,
        ResourceLoaderAware {
    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        System.out.println("ApplicationContextAware 回调");
    }
    @Override
    public void setApplicationEventPublisher(ApplicationEventPublisher applicationEventPublisher) {
        System.out.println("ApplicationEventPublisherAware 回调");
    }
    @Override
    public void setBeanClassLoader(ClassLoader classLoader) {
        System.out.println("BeanClassLoaderAware 回调");
    }
    @Override
    public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
        System.out.println("BeanFactoryAware 回调");
    }
    @Override
    public void setBeanName(String name) {
        System.out.println("BeanNameAware 回调");
    }
    @Override
    public void setResourceLoader(ResourceLoader resourceLoader) {
        System.out.println("ResourceLoaderAware 回调");
    }
}

按照以下顺序执行：