Aware 接口

Aware接口是Spring提供的回调机制，让Bean获取容器内部资源。

接口层次结构

Aware (顶层接口)
├── BeanNameAware
├── BeanFactoryAware
├── ApplicationContextAware
├── EnvironmentAware
├── ResourceLoaderAware
├── MessageSourceAware
├── ApplicationEventPublisherAware
├── ServletContextAware (Web环境)
└── ServletConfigAware (Web环境)

Aware接口列表

实现示例

BeanNameAware

@Component
public class MyBean implements BeanNameAware {

    private String beanName;

    @Override
    public void setBeanName(String name) {
        this.beanName = name;
        System.out.println("Bean名称: " + name);
    }

    public String getBeanName() {
        return beanName;
    }
}

ApplicationContextAware

@Component
public class ContextAwareBean implements ApplicationContextAware {

    private ApplicationContext context;

    @Override
    public void setApplicationContext(ApplicationContext context) {
        this.context = context;
    }

    public void publishEvent(ApplicationEvent event) {
        context.publishEvent(event);
    }

    public Object getBean(String name) {
        return context.getBean(name);
    }

    public Environment getEnvironment() {
        return context.getEnvironment();
    }
}

EnvironmentAware

@Component
public class EnvironmentAwareBean implements EnvironmentAware {

    private Environment environment;

    @Override
    public void setEnvironment(Environment environment) {
        this.environment = environment;
    }

    public String getProperty(String key) {
        return environment.getProperty(key);
    }

    public String getActiveProfile() {
        return environment.getActiveProfiles()[0];
    }
}

ResourceLoaderAware

@Component
public class ResourceLoaderBean implements ResourceLoaderAware {

    private ResourceLoader resourceLoader;

    @Override
    public void setResourceLoader(ResourceLoader resourceLoader) {
        this.resourceLoader = resourceLoader;
    }

    public Resource loadResource(String location) {
        return resourceLoader.getResource(location);
    }

    public InputStream loadFile(String path) throws IOException {
        return resourceLoader.getResource(path).getInputStream();
    }
}

组合实现多个Aware接口

@Component
public class FullAwareBean implements
        BeanNameAware,
        BeanFactoryAware,
        ApplicationContextAware,
        EnvironmentAware {

    private String beanName;
    private BeanFactory beanFactory;
    private ApplicationContext context;
    private Environment environment;

    @Override
    public void setBeanName(String name) {
        this.beanName = name;
    }

    @Override
    public void setBeanFactory(BeanFactory beanFactory) {
        this.beanFactory = beanFactory;
    }

    @Override
    public void setApplicationContext(ApplicationContext context) {
        this.context = context;
    }

    @Override
    public void setEnvironment(Environment environment) {
        this.environment = environment;
    }
}

调用时机

┌─────────────────────────────────────┐
│  Bean实例化                          │
├─────────────────────────────────────┤
│  属性注入                            │
├─────────────────────────────────────┤
│  Aware接口回调 ← 此时调用             │
├─────────────────────────────────────┤
│  BeanPostProcessor前置处理           │
├─────────────────────────────────────┤
│  @PostConstruct                      │
├─────────────────────────────────────┤
│  InitializingBean                    │
└─────────────────────────────────────┘

使用场景

@Component
public class EventPublisherBean implements ApplicationEventPublisherAware {

    private ApplicationEventPublisher publisher;

    @Override
    public void setApplicationEventPublisher(ApplicationEventPublisher publisher) {
        this.publisher = publisher;
    }

    public void notifyUserCreated(Long userId) {
        publisher.publishEvent(new UserCreatedEvent(this, userId));
    }
}

@Component
public class I18nBean implements MessageSourceAware {

    private MessageSource messageSource;

    @Override
    public void setMessageSource(MessageSource messageSource) {
        this.messageSource = messageSource;
    }

    public String getMessage(String code, Object[] args) {
        return messageSource.getMessage(code, args, LocaleContextHolder.getLocale());
    }
}

推荐替代方式

// 使用@Autowired替代Aware接口（推荐）
@Component
public class ModernBean {

    @Autowired
    private ApplicationContext context;

    @Autowired
    private Environment environment;

    @Autowired
    private ApplicationEventPublisher publisher;

    @Value("${bean.name}")
    private String beanNamePlaceholder;
}

要点总结

• Aware接口让Bean获取容器内部资源
• 在属性注入后、初始化前调用
• BeanNameAware获取Bean名称
• ApplicationContextAware获取完整容器
• 推荐使用@Autowired替代Aware接口 -Aware是Spring框架回调机制的基础