ApplicationContext在啟動(dòng)的時(shí)候就把所有的Bean全部實(shí)例化了拥娄。還可以為Bean配置lazy-init=true來讓Bean延遲實(shí)例化

ApplicationContext 應(yīng)用上下文抽活，繼承BeanFactory接口香府，它是Spring的更高級的容器，提供了更多的有用的功能

BeanFactory 與 ApplicationContext 區(qū)別器紧？

BeanFactory在啟動(dòng)的時(shí)候不會(huì)去實(shí)例化Bean，中有從容器中拿Bean的時(shí)候才會(huì)去實(shí)例化；
BeanFactory是Spring里面最低層的接口敦跌，提供了最簡單的容器的功能，只提供了實(shí)例化對象和拿對象的功能沸毁；

spring注入ApplicationContext對象的三種方式

第一種:直接注入
@Component
public class User {
 
    @Autowired
    private ApplicationContext applicationContext;
 
    public void show(){
        System.out.println(applicationContext.getClass().getName());
    }
}

第二種方式:構(gòu)造器注入

@Component
public class Bank {
    private ApplicationContext applicationContext;
 
    public Bank(ApplicationContext applicationContext) {
        this.applicationContext = applicationContext;
    }
 
    public  void show(){
        System.out.println(applicationContext.getClass().getName()+"===========");
    }
}


第三種:實(shí)現(xiàn)接口方式

@Component
public class Book implements ApplicationContextAware{

    private ApplicationContext applicationContext;

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

    public  void show(){
        System.out.println(applicationContext.getClass().getName());
    }
}

spring事件機(jī)制（訂閱發(fā)布模式 == 觀察者模式）

ApplicationContext事件機(jī)制是觀察者設(shè)計(jì)模式的 實(shí)現(xiàn)峰髓，通過ApplicationEvent類和ApplicationListener接口傻寂，可以實(shí)現(xiàn)ApplicationContext事件處理。

如果容器中有一個(gè)ApplicationListener Bean携兵，每當(dāng)ApplicationContext發(fā)布ApplicationEvent時(shí)疾掰，ApplicationListener Bean將自動(dòng)被觸發(fā)。

ApplicationEvent：容器事件徐紧，必須由ApplicationContext發(fā)布静檬；
ApplicationListener：監(jiān)聽器，可由容器中的任何監(jiān)聽器Bean擔(dān)任并级。

定義容器事件

public class EmailEvent extends ApplicationEvent{  
    private static final long serialVersionUID = 1L;  
    //屬性  
    private String address;  
    private String text;  
    //構(gòu)造方法  
    public EmailEvent(Object source) {  
        super(source);  
    }  
    public EmailEvent(Object source, String address, String text) {  
        super(source);  
        this.address = address;  
        this.text = text;  
    }  
    //getter和setter設(shè)置  
    public String getAddress() {  
        return address;  
    }  
    public void setAddress(String address) {  
        this.address = address;  
    }  
    public String getText() {  
        return text;  
    }  
    public void setText(String text) {  
        this.text = text;  
    }  
}  

定義監(jiān)聽器

port org.springframework.context.ApplicationEvent;  
import org.springframework.context.ApplicationListener;  
/** 
 * email之監(jiān)聽類 
 * 容器事件的監(jiān)聽器類     必須實(shí)現(xiàn)ApplicationListener接口
 */  
public class EmailNotifier implements ApplicationListener<ApplicationEvent>{  
  
    @Override  
    public void onApplicationEvent(ApplicationEvent event) {  
        if(event instanceof EmailEvent){  
            EmailEvent emailEvent = (EmailEvent) event;  
            System.out.println("email's address:"+emailEvent.getAddress());  
            System.out.println("email's text:"+emailEvent.getText());  
        } else {  
            System.out.println("the Spring's event:"+event);  
        }  
    }  
  
}  

將監(jiān)聽器注入到spring容器

Xml代碼
<!-- 配置事件監(jiān)聽 -->  
<bean class="com.cxg.test.springPlatfrom.EmailNotifier" /> 

測試

public class SpringTest {  
    public static void main(String arg[]){  
        //讀取Spring容器的配置文件  
        @SuppressWarnings("resource")  
        ApplicationContext applicationContext=new ClassPathXmlApplicationContext("application.xml");  
        //創(chuàng)建一個(gè)事件對象  
        EmailEvent emailEvent = new EmailEvent("hello ApplicationContext !", "demo@qq.com", "This is a test!");  
        //主動(dòng)觸發(fā)事件監(jiān)視機(jī)制  
        applicationContext.publishEvent(emailEvent);  
    }  
}