Listener--域对象属性变化监听器（[ServletRequest | HttpSession | ServletContext] AttributeListener）API详解

太过爱你忘了你带给我的痛 2021-08-13 12:33 351阅读 0赞

#### 监听三大域对象的属性变化的监听器 ####

*  ServletRequestAttributeListener
 *  ServletContextAttributeListener
 *  HttpSessionAttributeListener

#### 域对象的通用方法： ####

*  **setAttribute(name, value):**  
    触发添加属性的监听器的方法  
    触发修改属性的监听器的方法
 *  **getAttribute(name):**
 *  **removeAttribute(name):**  
    触发删除属性的监听器的方法

#### ServletContextAttibuteListener监听器的方法 ####

//监听添加属性的方法
    @Override
    public void attributeAdded(ServletContextAttributeEvent scab){ 
    	//获取到添加的属性
    	System.out.println("添加属性：" + scab.getName() + ":" + scab.getValue());
    }

//监听删除属性的方法
    @Override
    public void attributeRemoved(ServletContextAttributeEvent scab){ 
    	//获取到删除的属性
    	System.out.println("删除属性：" + scab.getName() + ":" + scab.getValue());
    }

//监听修改属性的方法
    @Override
    public void attributeReplaced(ServletContextAttributeEvent scab){ 
    	//获取到修改的属性
    	System.out.println("修改属性：" + scab.getName() + ":" + scab.getValue());
    }

#### HttpSessionAttributeListener监听器（同上） ####

#### ServletRequestAriibuteListenr监听器（同上） ####

#### 实例： ####

监听器：

package pers.zhang.listener;
    
    import javax.servlet.*;
    import javax.servlet.http.HttpSessionAttributeListener;
    import javax.servlet.http.HttpSessionBindingEvent;
    
    /** * @author zhang * @date 2019/9/20 - 8:53a */
    
    
    public class MyAttributeListener implements ServletRequestAttributeListener, HttpSessionAttributeListener, ServletContextAttributeListener { 
    
        //监听ServletContext属性添加
        @Override
        public void attributeAdded(ServletContextAttributeEvent scab) { 
            System.out.println("添加属性：" + scab.getName() + ":" + scab.getValue());
        }
    
        //监听ServletContext属性删除
        @Override
        public void attributeRemoved(ServletContextAttributeEvent scab) { 
            System.out.println("删除属性：" + scab.getName() + ":" + scab.getValue());
        }
    
        //监听ServletContext属性修改
        @Override
        public void attributeReplaced(ServletContextAttributeEvent scab) { 
            System.out.println("修改属性：" + scab.getName() + ":" + scab.getValue());
        }
    
        //监听ServletRequest属性增加
        @Override
        public void attributeAdded(ServletRequestAttributeEvent srab) { 
            System.out.println("添加属性：" + srab.getName() + ":" + srab.getValue());
        }
    
        //监听ServletRequest属性删除
        @Override
        public void attributeRemoved(ServletRequestAttributeEvent srab) { 
            System.out.println("删除属性：" + srab.getName() + ":" + srab.getValue());
        }
    
        //监听ServletRequest属性修改
        @Override
        public void attributeReplaced(ServletRequestAttributeEvent srab) { 
            System.out.println("修改属性：" + srab.getName() + ":" + srab.getValue());
        }
    
        //监听HttpSession属性增加
        @Override
        public void attributeAdded(HttpSessionBindingEvent hsb) { 
            System.out.println("增加属性：" + hsb.getName() + ":" + hsb.getValue());
        }
    
        //监听HttpSession属性删除
        @Override
        public void attributeRemoved(HttpSessionBindingEvent hsb) { 
            System.out.println("删除属性：" + hsb.getName() + ":" + hsb.getValue());
        }
    
        //监听HttpSession属性修改
        @Override
        public void attributeReplaced(HttpSessionBindingEvent hsb) { 
            System.out.println("修改属性：" + hsb.getName() + ":" + hsb.getValue());
        }
    }

<listener>
            <listener-class>pers.zhang.listener.MyAttributeListener</listener-class>
        </listener>

Servlet：

package pers.zhang.servlet;
    
    import javax.servlet.ServletContext;
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import javax.servlet.http.HttpSession;
    import java.io.IOException;
    
    /** * @author zhang * @date 2019/9/20 - 10:16 */
    public class MyAtttibuteServlet extends HttpServlet { 
        protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 
            //request域
            //增加属性
            request.setAttribute("request","addRequest");
            //修改属性
            request.setAttribute("request", "updateRequest");
            //删除属性
            request.removeAttribute("request");
            System.out.println("************************************************************");
    
            //sesion域
            HttpSession session = request.getSession(true);
            //增加属性
            session.setAttribute("session", "addSession");
            //修改属性
            session.setAttribute("session", "updateSession");
            //删除属性
            session.removeAttribute("session");
            System.out.println("************************************************************");
    
            //servletContext域
            ServletContext servletContext = getServletContext();
            //增加属性
            servletContext.setAttribute("servletContext", "addServletContext");
            //修改属性
            servletContext.setAttribute("servletContext", "updateServletContext");
            //删除属性
            servletContext.removeAttribute("servletContext");
    
        }
    
        protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 
            doPost(request, response);
        }
    }

配置：

<servlet>
            <servlet-name>myAttributeServlet</servlet-name>
            <servlet-class>pers.zhang.servlet.MyAtttibuteServlet</servlet-class>
        </servlet>
        <servlet-mapping>
            <servlet-name>myAttributeServlet</servlet-name>
            <url-pattern>/myAttribute</url-pattern>
        </servlet-mapping>

启动服务器，并访问/myAttribute，控制台输出：

修改属性：org.apache.catalina.ASYNC_SUPPORTED:true
    添加属性：request:addRequest
    修改属性：request:addRequest
    删除属性：request:updateRequest
    ************************************************************
    增加属性：session:addSession
    修改属性：session:addSession
    删除属性：session:updateSession
    ************************************************************
    添加属性：servletContext:addServletContext
    修改属性：servletContext:addServletContext
    删除属性：servletContext:updateServletContext