Java Web 開發(fā)從入門到實踐課件 第7章 - 過濾器和監(jiān)聽器

JavaWeb開發(fā)從入門到實踐JavaWebDevelopmentFromIntroductiontoPractice過濾器和監(jiān)聽器Chap07提綱過濾器和監(jiān)聽器過濾器和監(jiān)聽器分別用于處理用戶輸入的事件和動態(tài)監(jiān)控應用程序的狀態(tài)變化。7.1過濾器7.2監(jiān)聽器7.3本章小結7.1過濾器7.1.1過濾器的概念7.1.2配置過濾器7.1.3過濾器的生命周期7.1.4過濾器的鏈及執(zhí)行順序7.1.5過濾器的應用7.1.1過濾器的概念過濾器（Filter）的作用就是把瀏覽器對資源的請求攔截下來。圖

7-1

過濾器的工作原理7.1.1過濾器的概念過濾器需要實現(xiàn)jakarta.servlet.Filter接口publicvoidinit(FilterConfigfilterConfig)throwsServletException{}

publicvoiddoFilter(ServletRequestservletRequest,ServletResponseservletResponse,FilterChainfilterChain)throwsIOException,ServletException{}

publicvoiddestroy(){}init()方法該方法用來初始化過濾器對象doFilter()方法該方法是主要實現(xiàn)過濾的方法destroy()方法該方法的作用是釋放過濾器中使用的資源，是在關閉Web服務器時執(zhí)行

7.1.2配置過濾器配置過濾器有兩種方法一是在web.xml中配置二是通過注解配置<filter>

<filter-name>myFilter</filter-name>

<filter-class>com.swxy.filter.MyFilter</filter-class></filter>

<filter-mapping>

<filter-name>myFilter</filter-name>

<url-pattern>/*</url-pattern>

</filter-mapping>@WebFilter(filterName="myFilter",

//指定Filter的name屬性，等價于<filter-name>標簽 urlPatterns="/*",

//指定Filter的URL匹配模式

initParams={

//設置過濾器的初始參數(shù)

@WebInitParam(name="username",value="Charles")})

publicclassMyFilterimplementsFilter{//省略}7.1.3過濾器的生命周期過濾器的生命周期是：實例化→初始化→過濾→銷毀。圖

7-2

過濾器和Servlet的生命周期7.1.3過濾器的生命周期案例：過濾器、Servlet的生命周期示例MyFilter.java@WebFilter("/*")

publicclassMyFilterimplementsFilter{

publicMyFilter(){

System.out.println("Filter構造方法");

}

@Override

publicvoidinit(FilterConfigfilterConfig)throwsServletException{

System.out.println("Filter初始化");

}

7.1.3過濾器的生命周期@Override

publicvoiddoFilter(ServletRequestservletRequest,ServletResponseservletResponse,FilterChainfilterChain)throwsIOException,ServletException{

System.out.println("過濾前");

filterChain.doFilter(servletRequest,servletResponse);//放行

System.out.println("過濾后");

}

@Override

publicvoiddestroy(){

System.out.println("Filter銷毀方法");

}

}7.1.3過濾器的生命周期@WebServlet("/myServlet") publicclassMyServletextendsHttpServlet{ publicMyServlet(){System.out.println("Servlet構造方法");} @Override publicvoidinit()throwsServletException{ System.out.println("Servlet初始化方法"); } @Override protectedvoidservice(HttpServletRequestreq,HttpServletResponseresp)throwsServletException,IOException{ System.out.println("Servlet的service()方法"); } @Override publicvoiddestroy(){ System.out.println("Servlet銷毀方法"); } }MyServlet.java7.1.3過濾器的生命周期查看測試結果Filter構造方法Filter初始化Servlet構造方法Servlet初始化方法過濾前Servlet的service()方法過濾后Servlet銷毀方法Filter銷毀方法7.1.4過濾器的鏈及執(zhí)行順序過濾器鏈是指在一個Web應用，可以配置多個過濾器，這些過濾器稱為過濾器鏈。圖

7-3

過濾器鏈過濾器鏈7.1.4過濾器的鏈及執(zhí)行順序執(zhí)行過濾器1的放行前邏輯代碼執(zhí)行過濾器1的放行代碼執(zhí)行過濾器2的放行前邏輯代碼執(zhí)行過濾器2的放行代碼執(zhí)行過濾器3的放行前邏輯代碼執(zhí)行過濾器3的放行代碼訪問Web資源執(zhí)行過濾器3的放行后邏輯代碼執(zhí)行過濾器2的放行后邏輯代碼執(zhí)行過濾器1的放行后邏輯代碼7.1.4過濾器的鏈及執(zhí)行順序過濾器的執(zhí)行順序過濾器的攔截路徑相同時：首先按照<filter-mapping>標記在web.xml中出現(xiàn)的先后順序執(zhí)行過濾器然后接照過濾器類名的字典順序執(zhí)行注解的過濾器。7.1.5過濾器的應用JavaWeb過濾器是一種用于攔截、處理和修改請求和響應的組件，用于實現(xiàn)一些通用的功能字符編碼轉換過濾器1、EncodingFilter.java@WebFilter(urlPatterns="/*", initParams={@WebInitParam(name="encoding",value="UTF-8")})

publicclassEncodingFilterimplementsFilter{

privateStringencoding="";

@Override

publicvoidinit(FilterConfigfilterConfig)throwsServletException{

this.encoding=filterConfig.getInitParameter("encoding");

}

7.1.5過濾器的應用@Override

publicvoiddoFilter(ServletRequestservletRequest,ServletResponseservletResponse,FilterChainfilterChain)throwsIOException,ServletException{

HttpServletRequestrequest=(HttpServletRequest)servletRequest;

//轉子接口

HttpServletResponseresponse=(HttpServletResponse)servletResponse;//轉子接口

Stringmethod=request.getMethod();//獲取請求方式（如GET、POST等）

if("POST".equals(method)){//請求方式為POST時，中文亂碼的處理

request.setCharacterEncoding(encoding);

}else{//請求方式為GET時，中文亂碼的處理

Enumeration<String>parameterNames=request.getParameterNames();

while(parameterNames.hasMoreElements()){

Stringelement=parameterNames.nextElement();

Stringvalue=request.getParameter(element);

if(value!=null&&!"".equals(value)){

value=newString(value.trim().getBytes("ISO-8859-1"),encoding);

}

}

}filterChain.doFilter(servletRequest,servletResponse);//過濾器放行

}

7.1.5過濾器的應用 @Override

publicvoiddestroy(){

Filter.super.destroy();

}

}2、EncodingFilter.java@WebServlet("/encodingServlet")

publicclassEncodingServletextendsHttpServlet{

@Override

protectedvoiddoGet(HttpServletRequestreq,HttpServletResponseresp)throwsServletException,IOException{

Stringusername=req.getParameter("username");System.out.println(username);

}

}7.1.5過濾器的應用臟字過濾器1、準備屬性文件perties。在項目src下新建文件夾“resource”，在該文件夾下創(chuàng)建文件perties狗屁=***廢物=***該文件經(jīng)過native2ascii編碼后才能使用，命令語法如下：native2ascii-encodingutf-8源文件轉換后文件7.1.5過濾器的應用2、定義響應器包裝類publicclassReplaceWrapperextendsHttpServletResponseWrapper{

privateCharArrayWritercharWriter=newCharArrayWriter();

publicReplaceWrapper(HttpServletResponseresponse){

super(response);//必須調用父類構造方法

}

publicPrintWritergetWriter()throwsIOException{

returnnewPrintWriter(charWriter);//字符數(shù)組緩存輸出內容

}

publicCharArrayWritergetCharWriter(){

returncharWriter;

}

}7.1.5過濾器的應用3、定義用來替換臟字的過濾器@WebFilter(urlPatterns="/*",initParams={@WebInitParam(name="path",value="resource/perties")})publicclassReplaceFilterimplementsFilter{ privatePropertiesproperties=newProperties(); @Override publicvoidinit(FilterConfigfilterConfig)throwsServletException{

Stringpath=filterConfig.getInitParameter("path");//獲取初始化參數(shù)（文件名） try{ //加載資源文件 properties.load(ReplaceFilter.class.getClassLoader().getResourceAsStream(path)); }catch(Exceptione){ e.printStackTrace(); }

}

7.1.5過濾器的應用 @Override publicvoiddoFilter(ServletRequestservletRequest,ServletResponseservletResponse,FilterChainfilterChain)throwsIOException,ServletException{

HttpServletResponseresponse=(HttpServletResponse)servletResponse; ReplaceWrapperresp=newReplaceWrapper(response);//實例化響應器包裝類 filterChain.doFilter(servletRequest,resp); Stringstr=resp.getCharWriter().toString();//緩存輸出字符 for(Objecto:properties.keySet()){//循環(huán)文件(如：perties)中的key Stringkey=(String)o;

str=str.replace(key,properties.getProperty(key));//替換非法字符 } PrintWriterout=response.getWriter();//使用原來的HttpServletResponse輸出字符 out.write(str); }}7.1.5過濾器的應用@WebServlet("/replaceFilterServlet")publicclassReplaceFilterServletextendsHttpServlet{ @Override protectedvoiddoGet(HttpServletRequestreq,HttpServletResponseresp)throwsServletException,IOException{ resp.setContentType("text/html;charset=UTF-8"); PrintWriterout=resp.getWriter(); out.println("<!DOCTYPEhtml>"); out.println("<HTML>"); out.println("<HEAD><TITLE>臟字過濾器的使用</TITLE></HEAD>"); out.println("helloeveryone！大家好<br/>狗屁<br/>廢物"); out.println("</HTML>"); out.flush(); out.close(); }}4、編寫一個Servlet用來測試臟字過濾器7.1.5過濾器的應用5、測試結果圖

7-5

測試臟字過濾器7.2監(jiān)聽器7.2.1監(jiān)聽對象生命周期的監(jiān)聽器7.2.2監(jiān)聽對象屬性的監(jiān)聽器7.2.3監(jiān)聽Session對象狀態(tài)變化的監(jiān)聽器7.2監(jiān)聽器表

7-1

監(jiān)聽器接口和方法類別監(jiān)聽接口方法生命周期監(jiān)聽器ServletContextListenervoidcontextInitialized(ServletContextEventsce)voidcontextDestroyed(ServletContextEventsce)HttpSessionListenervoidsessionCreated(HttpSessionEventse)voidsessionDestroyed(HttpSessionEventse)ServletRequestListenervoidrequestDestroyed(ServletRequestEventsre)voidrequestInitialized(ServletRequestEventsre)對象屬性監(jiān)聽器ServletContextAttributeListenervoidattributeAdded(ServletContextAttributeEventscae)voidattributeRemoved(ServletContextAttributeEventscae)voidattributeReplaced(ServletContextAttributeEventscae)HttpSessionAttributeListenervoidattributeAdded(HttpSessionBindingEventse)voidattributeRemoved(HttpSessionBindingEventse)voidattributeReplaced(HttpSessionBindingEventse)ServletRequestAttributeListenervoidattributeAdded(ServletRequestAttributeEventsrae)voidattributeRemoved(ServletRequestAttributeEventsrae)voidattributeReplaced(ServletRequestAttributeEventsrae)Session對象狀態(tài)變化監(jiān)聽器HttpSessionBindingListenervoidvalueBound(HttpSessionBindingEventevent)voidvalueUnbound(HttpSessionBindingEventevent)HttpSessionActivationListenervoidsessionWillPassivate(HttpSessionEventse)voidsessionDidActivate(HttpSessionEventse)在Web應用中，監(jiān)聽器是指應用通過監(jiān)聽事件來監(jiān)聽請求中的行為而創(chuàng)建的一組類。7.2.1監(jiān)聽對象生命周期的監(jiān)聽器監(jiān)聽對象生命周期的監(jiān)聽器有三個：ServletContextListener、HttpSessionListener和ServletRequestListener。ServletContextListener用于監(jiān)聽應用啟動和停止事件，提供了兩個抽象方法publicvoidcontextInitialized(ServletContextEventsce){}//已完成加載Web應用和初始化參數(shù)publicvoidcontextDestroyed(ServletContextEventsce){}//Web應用即將關閉7.2.1監(jiān)聽對象生命周期的監(jiān)聽器案例：ServletContextListener的使用1、MyServletContextListener類，實現(xiàn)ServletContextListener接口publicclassMyServletContextListenerimplementsServletContextListener{

@Override

publicvoidcontextInitialized(ServletContextEventsce){

ServletContextservletContext=sce.getServletContext();//獲取ServletContext對象

Stringusername=servletContext.getInitParameter("username");//獲取初始化值

System.out.println("參數(shù)username："+username);

}

@Override

publicvoidcontextDestroyed(ServletContextEventsce){

System.out.println("釋放資源");

}

}7.2.1監(jiān)聽對象生命周期的監(jiān)聽器2、在web.xml中配置監(jiān)聽器<context-param> <param-name>username</param-name> <param-value>Charles</param-value></context-param><listener> <listener-class>com.swxy.listener.MyServletContextListener</listener-class></listener>圖

7-6

啟動服務器獲取初始化參數(shù)3、啟動服務器Tomcat7.2.1監(jiān)聽對象生命周期的監(jiān)聽器HttpSessionListenerHttpSessionListener接口提供了二個抽象方法voidsessionCreated(HttpSessionEventse){}//創(chuàng)新了新的會話

voidsessionDestroyed(HttpSessionEventse){}//銷毀了一個會話7.2.1監(jiān)聽對象生命周期的監(jiān)聽器案例：利用HttpSessionListener統(tǒng)計在線人數(shù)1、創(chuàng)建類MyHttpSessionListener實現(xiàn)HttpSessionListener接口packagecom.swxy.listener;

//導入包省略

@WebListener

publicclassMyHttpSessionListenerimplementsHttpSessionListener{

intonline=1;//記錄在線人數(shù)

@Override

publicvoidsessionCreated(HttpSessionEventse){

ServletContextservletContext=se.getSession().getServletContext();//獲取Application對象

Objectcount=servletContext.getAttribute("count");

if(count!=null){

online=Integer.parseInt(count.toString());

online++;//創(chuàng)建Session時，在線人數(shù)+1

}

servletContext.setAttribute("count",online);//在線人數(shù)存儲到Application作用域中

7.2.1監(jiān)聽對象生命周期的監(jiān)聽器}@Override

publicvoidsessionDestroyed(HttpSessionEventse){

ServletContextservletContext=se.getSession().getServletContext();

Objectcount=servletContext.getAttribute("count");

if(count!=null){

online=Integer.parseInt(count.toString());

online--;//銷毀Session對象時，在線人數(shù)-1

}

servletContext.setAttribute("count",online);

}

}7.2.1監(jiān)聽對象生命周期的監(jiān)聽器2、創(chuàng)建類OnLineServlet繼承HttpServlet@WebServlet("/OnLineServlet")publicclassOnLineServletextendsHttpServlet{ @Override protectedvoidservice(HttpServletRequestreq,HttpServletResponseresp)throwsServletException,IOException{ resp.setContentType("text/html;charset=UTF-8");//設置響應類型及編碼 HttpSessionsession=req.getSession();//創(chuàng)建Session對象 Stringlogout=req.getParameter("logout"); if("true".equals(logout)){ session.invalidate(); }

7.2.1監(jiān)聽對象生命周期的監(jiān)聽器2、創(chuàng)建類OnLineServlet繼承HttpServlet Integercount=(Integer)session.getServletContext().getAttribute("count");//獲取在線人數(shù) PrintWriterout=resp.getWriter(); out.write("<h2>在線人數(shù)："+count+"</h2>"); out.write("<h3><ahref='OnLineServlet?logout=true'>注銷</a></h3>"); }}3、測試結果圖

7-7

運行結果圖

7-8

點擊注銷后的運行結果7.2.1監(jiān)聽對象生命周期的監(jiān)聽器ServletRequestListenerServletRequestListener接口提供了二個抽象方法publicvoidrequestInitialized(ServletRequestEventsre){}//創(chuàng)建了新的Request對象publicvoidrequestDestroyed(ServletRequestEventsre){}//已經(jīng)銷毀了Request對象在Web應用中，有以下兩種方式配置ServletRequestListener1、在web.xml文件中配置<listener>

<listener-class>com.swxy.listener.MyServletRequestListener</listener-class></listener>2、注解方式@WebListenerpublicclassMyServletRequestListenerimplementsServletRequestListener{}7.2.2監(jiān)聽對象屬性的監(jiān)聽器監(jiān)聽對象生命周期的監(jiān)聽器有三個：ServletContextAttributeListener、HttpSessionAttributeListener、ServletRequestAttributeListener。ServletContextAttributeListenerServletContextAttributeListener接口提供了三個抽象方法voidattributeAdded(ServletContextAttributeEventscae){}//屬性被添加到Application中時調用voidattributeRemoved(ServletContextAttributeEventscae){}//屬性從Application中移除時調

voidattributeReplaced(ServletContextAttributeEventscae){}//屬性被修改時調用在Web應用中，有以下兩種方式配置ServletContextAttributeListener。1、在web.xml文件中配置<listener>

<listener-class>com.swxy.listener.MyServletContextAttributeListener</listener-class></listener>7.2.2監(jiān)聽對象屬性的監(jiān)聽器2、注解方式@WebListenerpublicclassMyServletContextAttributeListenerimplementsServletContextAttributeListener{}7.2.2監(jiān)聽對象屬性的監(jiān)聽器HttpSessionAttributeListenervoidattributeAdded(HttpSessionBindingEventse){}//屬性被添加到Session中時調用voidattributeRemoved(HttpSessionBindingEventse){}//屬性從Session中移除時調用voidattributeReplaced(HttpSessionBindingEventse){}//屬性被修改時調用HttpSessionAttributeListener接口提供了三個抽象方法ServletRequestAttributeListenervoidattributeAdded(ServletRequestAttributeEventsrae){}//屬性被添加到Request中時調用voidattributeRemoved(ServletRequestAttributeEventsrae){}//屬性從Request中移除時調用voidattributeReplaced(ServletRequestAttributeEventsrae){}//屬性被修改時調用ServletRequestAttributeListener接口可以用來監(jiān)聽Request對象加入屬性、移除屬性和替換屬性時響應的動作事件，該接口提供了三個抽象方法在Web應用中，配置方式同樣有二種方式：在web.xml中配置和注解，與ServletContextAttributeListener配置類似。7.2.3監(jiān)聽Session對象狀態(tài)變化的監(jiān)聽器監(jiān)聽Session對象狀態(tài)變化的監(jiān)聽器有二個：HttpSessionBindingListener和HttpSessionActivationListenerHttpSessionBindingListenerHttpSessionBindingListener是“HttpSession對象綁定監(jiān)聽器”，用來監(jiān)聽HttpSession中，設置成HttpSession屬性或從HttpSession中移除時得到Session的通知。voidvalueBound(HttpSessionBindingEventevent){}//已經(jīng)綁定一個Session范圍的對象或者變量voidvalueUnbound(HttpSessionBindingEventevent){}//已經(jīng)解綁了Session范圍的對象或者變量HttpSessionActivationListenerHttpSessionActivationListener是“HttpSession對象轉移監(jiān)聽器”，HttpSessionActivationListener的實現(xiàn)類也必須實現(xiàn)Serializable接口voidsessionWillPassivate(HttpSessionEventse){}//session中的對象持久化到存儲設備時調用voidsessionDidActivate(HttpSessionEventse){}//對象被重新加載時執(zhí)行該方法7.2.3監(jiān)聽Session對象狀態(tài)變化的監(jiān)聽器應用實例創(chuàng)建類MyHttpSessionBindingActivationListenerpublicclassMyHttpSessionBindingActivationListenerimplementsHttpSessionBindingListener,

HttpSessionActivationListener,Serializable{

@Override

publicvoidsessionWillPassivate(Ht