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前言

ApplicationContext是Spring应用程序中的中央接口，由于继承了多个组件，使得ApplicationContext拥有了许多Spring的核心功能，如获取bean组件，注册监听事件，加载资源文件等。ApplicationContext接口定义如下：

public interface ApplicationContext extends 
		EnvironmentCapable, 
		ListableBeanFactory, 
		HierarchicalBeanFactory,
		MessageSource, 
		ApplicationEventPublisher, 
		ResourcePatternResolver{}

• EnvironmentCapable：获取运行时环境
• ListableBeanFactory：获取beanNames的功能
• HierarchicalBeanFactory：获BeanFactory的功能
• MessageSource：集成消息解析器
• ApplicationEventPublisher：事件监听
• ResourcePatternResolver：资源解析器

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一、@Autowired（@Resouce）注入

@Component
public class ApplicationContextProvider1 {

    @Autowired
    private ApplicationContext applicationContext;

    @Bean("user01")
    public User user(){
        return new User("zhangsan",18);
    }

    @Bean("printApplicationContext01")
    public void printApplicationContext(){
        System.out.println(applicationContext.getBean("user01"));
    }
}

二、实现ApplicationContextAware接口（推荐）

@Component
public class ApplicationContextProvider2 implements ApplicationContextAware {

    private ApplicationContext applicationContext;

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        this.applicationContext = applicationContext;
    }

    @Bean("user02")
    public User user(){
        return new User("lisi",19);
    }

    @Bean("printApplicationContext02")
    public void printApplicationContext(){
        System.out.println(applicationContext.getBean("user02"));
    }
}

三、构造器方法注入

利用Spring4.3特性

• 构造函数只能有一个，如果有多个，就必须有一个无参数的构造函数，此时，Spring会调用无参数的构造函数
• 构造函数的参数，必须在Spring容器中存在

@Component
public class ApplicationContextProvider3 {

    private ApplicationContext applicationContext;

    public ApplicationContextProvider3(ApplicationContext applicationContext) {
        this.applicationContext = applicationContext;
    }

    @Bean("user03")
    public User user(){
        return new User("wangwu",20);
    }

    @Bean("printApplicationContext03")
    public void printApplicationContext(){
        System.out.println(applicationContext.getBean("user03"));
    }
}