一.過濾器Filter

對(duì)指定的web資源進(jìn)行攔截,實(shí)現(xiàn)一些特殊功能,如實(shí)現(xiàn)URL權(quán)限訪問鸦泳、過濾敏感詞等等

1).注冊過濾器

方式一
    在WEB-INF/web.xml注冊
    <filter>
        <filter-name>filter</filter-name>
        <filter-class>com.xxx.xxFilter</filter-class>
        <init-param>
            <param-name>name1</param-name>
            <param-value>value1</param-value>
        </init-param>
    </filter>
    <filter-mapping>
        <filter-name>filter</filter-name>       
        <url-pattern>/*</url-pattern> 指定要攔截的url
        <servlet-name>xxxServlet</servlet-name> 指定要攔截的Servlet
        <dispatcher>REQUEST</dispatcher> 指定要攔截資源的訪問方式是REQUEST/FORWARD/INCLUDE/ERROR,默認(rèn)REQUEST
    </filter-mapping>

方式二
    在com.xxx.xxFilter類添加注解
    @WebFilter(filterName="filter",urlPatterns={"/*"},servletNames={"Demo1Servlet"})

2).實(shí)現(xiàn)接口

創(chuàng)建: web應(yīng)用加載時(shí),創(chuàng)建所有過濾器對(duì)象,調(diào)用init()初始化,一直駐留內(nèi)存;
銷毀: web應(yīng)用移除時(shí),銷毀所有過濾器對(duì)象,銷毀前調(diào)用destroy()善后 
public class xxFilter implements Filter {
    public void destroy() {     
    }

    // 每次攔截資源后調(diào)用
    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {
        FilterChain過濾器鏈對(duì)象,一個(gè)資源可能被多個(gè)過濾器所攔截,攔截順序是web.xml中filter-mapping配置順序
        FilterChain.doFilter()一旦被調(diào)用,就執(zhí)行過濾器鏈的下一個(gè)節(jié)點(diǎn),若當(dāng)前是最后過濾器,則執(zhí)行目標(biāo)資源
    }

    public void init(FilterConfig filterConfig) throws ServletException {
        filterConfig.getInitParameter(String name) 獲取web.xml過濾器配置信息
        filterConfig.getServletContext() 獲取ServletContext對(duì)象
    }
}

二.監(jiān)聽器Listener

Servlet監(jiān)聽器: 監(jiān)聽ServletContext、Session和Request域的變化词身。

1.監(jiān)聽三大作用域的創(chuàng)建和銷毀

1)注冊監(jiān)聽器
    方式一
    在WEB-INF/web.xml注冊
    <listener>
        <listener-class>com.xxx.xxx</listener-class>
    </listener>
    
    方式二
    在com.xxx.xxx類添加注解@WebListener

2)實(shí)現(xiàn)監(jiān)聽器接口
    public class xxx implements ServletContextListener {            
        // ServletContext創(chuàng)建: web應(yīng)用被加載時(shí)創(chuàng)建
        public void contextDestroyed(ServletContextEvent sce) {         
        }
        
        // ServletContext銷毀: web應(yīng)用被移除時(shí)銷毀
        public void contextInitialized(ServletContextEvent sce) {           
        }           
    }
    應(yīng)用場景: 保存全局對(duì)象,如:創(chuàng)建數(shù)據(jù)庫連接池; 加載框架配置文件;實(shí)現(xiàn)任務(wù)調(diào)度定時(shí)器

    public class xxx implements HttpSessionListener {
        // Session創(chuàng)建:首次調(diào)用request.getSession()時(shí)創(chuàng)建
        public void sessionCreated(HttpSessionEvent se) {
        }
        
        // Session銷毀:超30分鐘沒用時(shí)銷毀 /調(diào)用invalidate()銷毀 
        // 服務(wù)器非正常關(guān)閉時(shí)銷毀(正常關(guān)閉則被鈍化,再次開啟則被活化)
        public void sessionDestroyed(HttpSessionEvent se) {
        }
    }
    
    public class xxx implements ServletRequestListener {
        // Request創(chuàng)建:瀏覽器請(qǐng)求開始時(shí)創(chuàng)建     
        public void requestDestroyed(ServletRequestEvent sre) {         
        }
        
        // Request銷毀:瀏覽器請(qǐng)求結(jié)束時(shí)銷毀
        public void requestInitialized(ServletRequestEvent sre) {       
        }
    }

2.監(jiān)聽三大作用域?qū)傩缘脑鰟h改

public class xxx implements ServletContextAttributeListener {
    public void attributeAdded(ServletContextAttributeEvent scab) {
        System.out.println("屬性加入"+scab.getName()+":"+scab.getValue());
    }

    public void attributeRemoved(ServletContextAttributeEvent scab) {
        System.out.println("屬性移除"+scab.getName()+":"+scab.getValue());
    }

    public void attributeReplaced(ServletContextAttributeEvent scab) {
        System.out.println("屬性替換"+scab.getName()+":"+scab.getValue()+
        ":"+scab.getServletContext().getAttribute(scab.getName()));
    }
}

public class xxx implements HttpSessionAttributeListener {
    public void attributeAdded(HttpSessionBindingEvent se) {
    }

    public void attributeRemoved(HttpSessionBindingEvent se) {
    }

    public void attributeReplaced(HttpSessionBindingEvent se) {
    }
}

public class xxx implements ServletRequestAttributeListener {
    public void attributeAdded(ServletRequestAttributeEvent srae) {
    }
    public void attributeRemoved(ServletRequestAttributeEvent srae) {
    }
    public void attributeReplaced(ServletRequestAttributeEvent srae) {
    }
}

3.監(jiān)聽JavaBean對(duì)象在Session域中的變化

public class JavaBean類 implements HttpSessionBindingListener ,HttpSessionActivationListener{
    ...
    // javabean對(duì)象被綁到session
    public void valueBound(HttpSessionBindingEvent event) {         
    }
    
    // javabean對(duì)象被移出session
    public void valueUnbound(HttpSessionBindingEvent event) {           
    }
    
    // javabean對(duì)象隨session活化
    public void sessionDidActivate(HttpSessionEvent se) {
    }

    // javabean對(duì)象隨session鈍化
    public void sessionWillPassivate(HttpSessionEvent se) {
    }
}

簡書: http://www.reibang.com/p/46e5b3bf42d7
CSDN博客: http://blog.csdn.net/qq_32115439/article/details/54791009
GitHub博客：http://lioil.win/2017/01/30/Servlet-Listener.html
Coding博客：http://c.lioil.win/2017/01/30/Servlet-Listener.html