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一、Listener監(jiān)聽器

1、概念簡(jiǎn)介

JavaWeb三大組件：Servlet，Listener，Filter。監(jiān)聽器就是指在應(yīng)用程序中監(jiān)聽相關(guān)對(duì)象狀態(tài)變化的組件。

2、事件源對(duì)象

指被監(jiān)聽對(duì)象。

• ServletContext

ServletContextListener生命周期監(jiān)聽，它有兩個(gè)方法，出生時(shí)調(diào)用contextInitialized()，銷毀時(shí)調(diào)用contextDestroyed();

ServletContextAttributeListener屬性監(jiān)聽，它有三個(gè)方法，添加屬性attributeAdded()，替換屬性attributeReplaced()，移除屬性時(shí)attributeRemoved()。

• HttpSession

HttpSessionListener生命周期監(jiān)聽：它有兩個(gè)方法，出生時(shí)調(diào)用sessionCreated()，銷毀時(shí)調(diào)用sessionDestroyed()；

HttpSessioniAttributeListener屬性監(jiān)聽：它有三個(gè)方法，添加屬性attributeAdded()，替換屬性attributeReplaced()，移除屬性attributeRemoved()。

• ServletRequest

ServletRequestListener生命周期監(jiān)聽：它有兩個(gè)方法，出生時(shí)調(diào)用requestInitialized()，銷毀時(shí)調(diào)用requestDestroyed()；

ServletRequestAttributeListener屬性監(jiān)聽：它有三個(gè)方法，添加屬性attributeAdded()，替換屬性attributeReplaced()，移除屬性attributeRemoved()。

3、編碼案例

• 相關(guān)監(jiān)聽器

TheContextListener

public class TheContextListener implements ServletContextListener {@Overridepublic void contextInitialized(ServletContextEvent servletContextEvent) {System.out.println("初始化：TheContextListener");ServletContext servletContext = servletContextEvent.getServletContext() ;servletContext.setAttribute("author","cicada");}@Overridepublic void contextDestroyed(ServletContextEvent servletContextEvent) {System.out.println("銷毀：TheContextListener");} }

TheRequestListener

public class TheRequestListener implements ServletRequestListener {@Overridepublic void requestDestroyed(ServletRequestEvent servletRequestEvent) {System.out.println("初始化：TheRequestListener");}@Overridepublic void requestInitialized(ServletRequestEvent servletRequestEvent) {System.out.println("銷毀：TheRequestListener");} }

TheSessionListener

public class TheSessionListener implements HttpSessionListener {@Overridepublic void sessionCreated(HttpSessionEvent httpSessionEvent) {System.out.println("初始化：TheSessionListener");}@Overridepublic void sessionDestroyed(HttpSessionEvent httpSessionEvent) {System.out.println("銷毀：TheSessionListener");} }

RequestAttributeListener

public class RequestAttributeListener implements ServletRequestAttributeListener {@Overridepublic void attributeAdded(ServletRequestAttributeEvent evt) {System.out.println("Request添加屬性："+evt.getName()+";"+evt.getValue());}@Overridepublic void attributeRemoved(ServletRequestAttributeEvent evt) {System.out.println("Request移除屬性："+evt.getName()+";"+evt.getValue());}@Overridepublic void attributeReplaced(ServletRequestAttributeEvent evt) {System.out.println("Request替換屬性："+evt.getName()+";"+evt.getValue());} }

• web.xml配置文件

<!-- 監(jiān)聽器相關(guān)配置 --> <listener><listener-class>com.node05.servlet.listener.TheContextListener</listener-class> </listener> <listener><listener-class>com.node05.servlet.listener.TheSessionListener</listener-class> </listener> <listener><listener-class>com.node05.servlet.listener.TheRequestListener</listener-class> </listener> <listener><listener-class>com.node05.servlet.listener.RequestAttributeListener</listener-class> </listener> <session-config><!-- 設(shè)置session失效時(shí)間為1分鐘 --><session-timeout>1</session-timeout> </session-config>

• 測(cè)試接口

public class ListenerServletImpl extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {response.setContentType("text/html;charset=utf-8");// 1、獲取TheContextListener初始化數(shù)據(jù)ServletContext servletContext = this.getServletContext() ;String author = String.valueOf(servletContext.getAttribute("author")) ;System.out.println("TheContextListener Author:"+author);// 2、Request屬性設(shè)置request.setAttribute("mood","smile");request.setAttribute("mood","agitated");// 3、Session創(chuàng)建，1分鐘失效，調(diào)用銷毀HttpSession session = request.getSession(true) ;session.setAttribute("casually","casually");response.getWriter().print("Hello:Listener");} }

二、Filter過濾器

1、過濾器簡(jiǎn)介

客戶端請(qǐng)求Servlet時(shí)，先執(zhí)行相關(guān)Filter，如果Filter通過，則繼承執(zhí)行請(qǐng)求的Servlet；如果Filter不通過，則不會(huì)執(zhí)行用戶請(qǐng)求的Servlet。過濾器可以動(dòng)態(tài)地?cái)r截請(qǐng)求和響應(yīng)。

2、Filter接口

Filter接口定義了三個(gè)核心方法。

• init()

應(yīng)用程序啟動(dòng)時(shí)，服務(wù)器實(shí)例化Filter對(duì)象，并調(diào)用其init方法，讀取web.xml配置，完成對(duì)象的初始化加載。

• doFilter()

實(shí)際的過濾操作，請(qǐng)求達(dá)到服務(wù)器時(shí)，Servlet容器將先調(diào)用過濾器的doFilter方法。

• destroy()

容器在銷毀過濾器前調(diào)用該方法，釋放過濾器占用的資源。

3、編碼案例

• 編寫過濾器

public class ThePrintLogFilter implements Filter {@Overridepublic void init(FilterConfig filterConfig) throws ServletException {String myName = filterConfig.getInitParameter("myName") ;System.out.println("myName："+myName);}@Overridepublic void doFilter(ServletRequest servletRequest,ServletResponse servletResponse,FilterChain chain) throws IOException, ServletException {HttpServletRequest request = (HttpServletRequest)servletRequest ;HttpServletResponse response = (HttpServletResponse)servletResponse ;String name = request.getParameter("name") ;if (!name.equals("cicada")){response.getWriter().print("User Error !");return ;}chain.doFilter(servletRequest,servletResponse);}@Overridepublic void destroy() {System.out.println("ThePrintLogFilter destroy()");} }

• web.xml配置文件

<!-- 過濾器相關(guān)配置 --> <filter><filter-name>thePrintLogFilter</filter-name><filter-class>com.node05.servlet.filter.ThePrintLogFilter</filter-class><init-param><param-name>myName</param-name><param-value>cicada</param-value></init-param> </filter> <filter-mapping><filter-name>thePrintLogFilter</filter-name><url-pattern>/filterServletImpl</url-pattern> </filter-mapping>

• 測(cè)試接口

public class FilterServletImpl extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {response.setContentType("text/html;charset=utf-8");response.getWriter().print("Hello:Filter");} }

三、Interceptor攔截器

Spring框架中的攔截器Interceptor類似于Servlet中的過濾器Filter，主要用于攔截用戶請(qǐng)求并作相應(yīng)的處理。例如通過攔截器可以進(jìn)行權(quán)限驗(yàn)證、記錄請(qǐng)求信息的日志、判斷用戶是否登錄等。請(qǐng)求轉(zhuǎn)發(fā)不執(zhí)行攔截、過濾；重定向執(zhí)行攔截和過濾。

四、源代碼地址

GitHub·地址 https://github.com/cicadasmile/java-base-parent GitEE·地址 https://gitee.com/cicadasmile/java-base-parent

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