SpringBoot——Listener(监听器)的使用

朱雀 2022-11-06 01:58 154阅读 0赞

## 常用的监听器接口 ##

1.`ServletContextListener` – 监听`servletContext`对象的创建以及销毁

1.1    contextInitialized(ServletContextEvent arg0)   -- 创建时执行
    
    1.2    contextDestroyed(ServletContextEvent arg0)  -- 销毁时执行

2.`HttpSessionListener` – 监听`session`对象的创建以及销毁

2.2   sessionCreated(HttpSessionEvent se)   -- 创建时执行
    
    2.2   sessionDestroyed(HttpSessionEvent se) -- 销毁时执行

3.`ServletRequestListener` – 监听`request`对象的创建以及销毁

3.1    requestInitialized(ServletRequestEvent sre) -- 创建时执行
    
    3.2    requestDestroyed(ServletRequestEvent sre) -- 销毁时执行

4.`ServletContextAttributeListener` – 监听`servletContext`对象中属性的改变

4.1    attributeAdded(ServletContextAttributeEvent event) -- 添加属性时执行
    
    4.2    attributeReplaced(ServletContextAttributeEvent event) -- 修改属性时执行
    
    4.3    attributeRemoved(ServletContextAttributeEvent event) -- 删除属性时执行

5.`HttpSessionAttributeListener` \--监听`session`对象中属性的改变

5.1    attributeAdded(HttpSessionBindingEvent event) -- 添加属性时执行
    
    5.2    attributeReplaced(HttpSessionBindingEvent event) -- 修改属性时执行
    
    5.3    attributeRemoved(HttpSessionBindingEvent event) -- 删除属性时执行

6.`ServletRequestAttributeListener` \--监听`reques`t对象中属性的改变

6.1    attributeAdded(ServletRequestAttributeEvent srae) -- 添加属性时执行
    
    6.2    attributeReplaced(ServletRequestAttributeEvent srae) -- 修改属性时执行
    
    6.3    attributeRemoved(ServletRequestAttributeEvent srae) -- 删除属性时执行

# 创建Listener的两种方式，ServletContextListener举例 #

## 1、通过注解的方式 ##

创建一个类实现`ServletContextListener`的接口，在这个类上加`@WebListener`注解，并且在启动类加上`@ServletComponentScan`注解，这样就完成了。如果要改变监听器监听的对象，比如监听`session`对象，那就改成实现`HttpSessionListener`接口就行了

监听器类：

import javax.servlet.ServletContextEvent;
    import javax.servlet.ServletContextListener;
    
    import javax.servlet.annotation.WebListener;
    
    
    
    @WebListener
    public class ListenerDemo1 implements ServletContextListener { 
        @Override
        public void contextInitialized(ServletContextEvent sce) { 
            System.out.println("进入监听器");
        }
    
        @Override
        public void contextDestroyed(ServletContextEvent sce) { 
    
        }
    }

启动类：

@SpringBootApplication
    @ServletComponentScan
    @MapperScan(basePackages = { "wwfww.warehouse.mapper"})//不加这句mapper依赖注入不进来
    public class WarehouseApplication { 
    
        public static void main(String[] args) { 
            SpringApplication.run(WarehouseApplication.class, args);
        }
    
    
    
    
    }

控制台输出：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzA4NTc5Nw_size_16_color_FFFFFF_t_70]

## 2、在启动类注册`Listener` ##

创建一个类实现`ServletContextListener`接口，并且在启动类创建方法来注册就行了

监听器类：

import javax.servlet.ServletContextEvent;
    import javax.servlet.ServletContextListener;
    
    
    public class ListenerDemo1 implements ServletContextListener { 
        @Override
        public void contextInitialized(ServletContextEvent sce) { 
            System.out.println("进入监听器,方式二");
        }
    
        @Override
        public void contextDestroyed(ServletContextEvent sce) { 
    
        }
    }

启动类：

import org.springframework.boot.SpringApplication;
    import org.springframework.boot.autoconfigure.SpringBootApplication;
    import org.springframework.boot.web.servlet.ServletListenerRegistrationBean;
    import org.springframework.context.annotation.Bean;
    import tk.mybatis.spring.annotation.MapperScan;
    import wwfww.warehouse.aaaTest.listener.ListenerDemo1;
    
    @SpringBootApplication
    @MapperScan(basePackages = { "wwfww.warehouse.mapper"})//不加这句mapper依赖注入不进来
    public class WarehouseApplication { 
    
        public static void main(String[] args) { 
            SpringApplication.run(WarehouseApplication.class, args);
        }
    
        /** * 注册监听器Listener * * @return */
        @Bean
        public ServletListenerRegistrationBean get() { 
            ServletListenerRegistrationBean bean = new ServletListenerRegistrationBean(new ListenerDemo1());
            return bean;
        }
    
    
    }

输出：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzA4NTc5Nw_size_16_color_FFFFFF_t_70 1]

**补充：如果实现接口，但是IDEA没有提示你实现接口里面的方法，如下：**

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzA4NTc5Nw_size_16_color_FFFFFF_t_70 2]  
接口里面可以看到有两个方法的

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzA4NTc5Nw_size_16_color_FFFFFF_t_70 3]  
**解决办法：**

1、点击右键找到Generate  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzA4NTc5Nw_size_16_color_FFFFFF_t_70 4]

2、选择Override Methods

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzA4NTc5Nw_size_16_color_FFFFFF_t_70 5]

3、选择图中两个，点击OK就行了

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MzA4NTc5Nw_size_16_color_FFFFFF_t_70 6]

## [监听器的应用场景][Link 1] ##

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[Link 1]: https://blog.csdn.net/houpeibin2012/article/details/104449730