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SoEasy列ServletServlet介1.1.百ServletJavaappletJavaapplet用Java編程語言實現(xiàn)。在通信量大的服務器上，Javaservlet的優(yōu)點在于它們的執(zhí)行速度更快于CGI1.2.百AppletServletServletServletServletHTTPWebServletJavaSoftJavaWebServerJavaServlet什么Servlet的某些方法來完成整個處理過程的。ServletTomcatServlet容器Servlet是不用程序指定調用的。Web程序報錯。JavaEETomcatServlet\JSP版JavaEE版Java運行環(huán)Servlet2.3\JSPJavaEEJDKServlet2.4\JSPJavaEEJDKServlet2.5\JSPJavaEEJDKServlet3.0\JSPJavaEEJDK如果使用Tomcat服務器的高版本時，可以向下兼容Servlet\JSP、JavaEE及Java運行環(huán)境的版本。Servlet2.5JavaEEJavaEE5.0在Tomcat服務器與JavaEE中，分別提供了有關Servlet的幫助文檔信息。如果在Tomcat服務器中查看Servlet的相關信息在Tomcat服務器的安裝中，webapps 中的docs API幫助文檔。JavaEE提供了幫助文檔，TomcatServlet2.5版本的幫助文檔。編寫一Eclipse創(chuàng)建開發(fā)工具Eclipse或MyEclipse本身提供了創(chuàng)建Servlet的功能下面我們首先利用開發(fā)工具來創(chuàng)建Servlet，具體步驟如下：Web在Web工程的 下，鼠標“New”選項，選擇“Servlet”選項ServletServletServletServlet的包名、名稱及相關方法后，點擊“NextServletweb.xmlServlet/JSPClassName：ServletServlet/JSPName：ServletServlet/JSPMapURL：配置Servlet的路徑，客戶端通過該路徑ServletFilePathofweb.xmlweb.xmlDisyName：顯示名稱配置完畢之后，點擊“FinishServlet創(chuàng)建完成之后，當前Web工程的變化是在 下多了一個Servlet的Java文件，在WEB-web.xmlServlet相關配置信息。ServletJava文件內(nèi)容：publicclassFirstServletextendsHttpServletpublicvoidinit()throwsServletExceptionpublicvoiddoGet(HttpServletRequestrequest,HttpServletResponseresponse)throwsServletException,IOException{PrintWriterout=response.getWriter();out.println("<!DOCTYPEHTML>");out.println("<HEAD><TITLE>AServlet</TITLE></HEAD>");out.println("<BODY>");out.println(" Thisis"+this.getClass()+",usingtheGETout.println("</BODY>");}publicvoiddoPost(HttpServletRequestrequest,HttpServletResponseresponse)throwsServletException,IOException{PrintWriterout=response.getWriter();out.println("<!DOCTYPEHTML>");out.println("<HEAD><TITLE>AServlet</TITLE></HEAD>");out.println("<BODY>");out.println(" Thisis"+this.getClass()+",usingtheGETout.println("</BODY>");}publicvoiddestroy()}Webweb.xml<?xmlversion="1.0"encoding="UTF-<web-app <description>ThisisthedescriptionofmyJ2EE y-name>Thisisthedis ynameofmyJ2EE 將當前Web應用程序發(fā)布到Tomcat服務器，并啟動Tomcat服務器運試當前創(chuàng)建的EclipseMyEclipseWebTomcatTomcat，打開瀏覽器在地址欄中輸入servlet/servlet/FirstServlet服務器Servlet內(nèi)容。，Servlet手動編寫一個ServletHttpServletServletJavapublicpublicclassSecondServletextendsHttpServlet{publicvoidinit(throwsServletException}protectedvoiddoGet(HttpServletRequestreq,HttpServletResponsethrowsServletExceptionIOException}protectedvoiddoPost(HttpServletRequestreq,HttpServletResponseresp)throwsServletException,IOException{System.out.println("這是doPost()方法}publicvoidpublicvoiddestroy(){}}web.xml<?<?xmlversion="1.0"encoding="UTF-<web-app"h :用于配置Servlet的名稱和完整路徑servlet- :用于為對應的Servlet設置名稱servlet- :用于設置對應的Servlet的完整路徑servlet-servlet-url-:用于配置客戶端請求路徑:用于設置對應使用的Servlet名稱:路徑相對路徑絕對路徑 <<<將當前Web應用程序發(fā)布到Tomcat服務器，并啟動Tomcat服務器運試當前創(chuàng)建的EclipseMyEclipseWebTomcatTomcat打開瀏覽器，在地址欄中輸入servlet/servlet/SecondServlet，服Servlet內(nèi)容。EclipseMyEclipseconsoleServlet的繼承Method req, CalledbytheMethod req, Calledbytheserver(viatheservicemethod)toallowaservlettohandleaGET req, Calledbytheserver(viatheservicemethod)toallowaservlettohandleaPOST req, ReceivesstandardHTTPrequestsfromthepublicservicemethodanddispatchesthemtothedoXXXmethodsdefinedinthisclass. req, requeststotheprotectedserviceMethodCalledbytheservletcontainertoindicatetoaservletthattheservletisbeingtakenoutAconveniencemethodwhichcanbeoverriddensothatthere'snoneedtoMethodCalledbytheservletcontainertoindicatetoaservletthattheservletisbeingtakenoutAconveniencemethodwhichcanbeoverriddensothatthere'snoneedto req, CalledbytheservletcontainertoallowtheservlettorespondtoaMethodCalledbytheservletMethodCalledbytheservletcontainertoindicatetoaservletthattheservletisbeingtakenoutReturnsaServletConfigobject,whichcontainsinitializationandstartupparametersthisReturnsinformationabouttheservlet,suchasauthor,version,and Calledbytheservletcontainertoindicatetoaservletthattheservletisbeingced req, Calledbytheservletcontainertoallowtheservlettorespondtoa所以，initdestroyServlet接口提供的方法。通過上述的查找，我們已經(jīng)很清晰的知道Servlet的繼承關系，具體如下圖：Servlet工作流利用Servlet完成的Web應用的實際工作流程是通過Tomcat服務器發(fā)布服務客戶端與服務器端Http協(xié)議完成的。具體工作流程如下：TomcatServletWebweb.xmlServletServletTomcatServlet容器向客戶端瀏覽器進行響應。Servlet具體的工作流程。Servlet注意事值得注意的是Servlet內(nèi)容是屬于JavaEE內(nèi)容和使用JavaSE內(nèi)容一樣都是需要引入JAR包的。javaee.jarServlet的所有內(nèi)容。WebTomcat服務器的時候，發(fā)現(xiàn)對應的中并沒有javaee.jar包。JARTomcatServlet運行所需要的環(huán)境。在Tomcat服務器的安裝 中的lib 供了Servlet運行所需的環(huán)境。Servlet 中的 創(chuàng)建Web工程名稱 結構Servlet在對應Web工 中的web.xml進行配置深入掌Servlet的生命周一般情況下，自定義Servlet都是繼承HttpServlet。但通過HttpServlet的繼承鏈，我們知道HttpServletServletServletMethodCalledbytheservletcontainertoindicatetoaservletthattheservletisbeingtakenoutReturnsaServletConfigobject,whichcontainsinitializationandstartupparametersthisReturnsinformationabouttheservlet,suchasauthor,version,and Calledbytheservletcontainertoindicatetoaservletthattheservletisbeingced req, Calledbytheservletcontainertoallowtheservlettorespondtoa上述所有方法中，init()、service()destroy()Servlet的生命周期。下面我們分別討論一init()init()Servletinit()方法被正確執(zhí)行。ServletServletdestroy()Servlet實destroy()ServletServletServletpublicpublicclassLifeServletimplementsServletpublicSystem.out.println("這里創(chuàng)建了一個Servlet實例對象}publicvoidinit(ServletConfigconfigthrowsServletException}publicvoidservice(ServletRequestreq,ServletResponsethrowsServletExceptionIOException}publicvoiddestroy(){}publicServletConfiggetServletConfig()return}publicStringgetServletInfo()return}}web.xmlServlet<?<?xmlversion="1.0"encoding="UTF-<web-app" 九月12,20148:00:41下午org.apache.catalina.core.AprLifecycleListenerINFO:LoadedAPRbasedApacheTomcatNativelibrary1.1.31usingAPRversion九月12,20148:00:41下午org.apache.catalina.core.AprLifecycleListenerINFO:APRcapabilities:IPv6[true],sendfile[true],acceptfilters[false],random九月12,20148:00:42下午org.apache.catalina.core.AprLifecycleListenerinitializeSSLINFO:OpenSSLsuccessfullyinitialized(OpenSSL1.0.1h5Jun2014)九月12,20148:00:42下午org.apache.coyote. ProtocolinitINFO:InitializingProtocolHandler["http-apr-8080"]九月12,20148:00:42下午org.apache.coyote. ProtocolinitINFO:InitializingProtocolHandler["ajp-apr-8009"]九月12,20148:00:42下午org.apache.catalina.startup.CatalinaloadINFO:Initializationprocessedin1417ms九月12,20148:00:42下午org.apache.catalina.core.StandardServicestartInternalINFO:StartingserviceCatalina九月12,20148:00:42下午org.apache.catalina.core.StandardEnginestartInternalINFO:StartingServletEngine:ApacheTomcat/7.0.55九月12,20148:00:43下午org.apache.catalina.startup.HostConfigINFO:DeployingwebapplicationdirectoryC:\Tools\apache-tomcat-九月12,20148:00:43下午org.apache.catalina.startup.HostConfigINFO:DeploymentofwebapplicationdirectoryC:\Tools\apache-tomcat-7.0.55\webapps\08_servlethasfinishedin377ms九月12,20148:00:44下午org.apache.catalina.startup.CatalinaINFO:Serverstartupin1766ServletServletServletservice()方法來處理請求。第二次向Servletservice()Servletinit()方法。在停止Tomcat服務器時，Servletdestroy()方法被調用，釋放所使用的資源。Servlet的線程安在Servlet的整個生命周期中構造方法只被執(zhí)行一次也就是說Servlet的整個生命周期中，ServletServlet是單例多線程的，可能會引起線程安全問題。所謂線程安全就是一個Servlet實例對象會同時處理多個請求這樣的Servlet工作效率的確很高。Servlet中包含成員變量的話，可能一個線程對該成員變量進行寫操作，而另一個線程對該成Servlet不能創(chuàng)建成員變量。服務器啟動創(chuàng)建創(chuàng)建一個Servlet實例對象如果可以在Tomcat服務器啟動時進行創(chuàng)建實例對象并完成初始化工作，service()方法處理請求邏輯即可。web.xml<?<?xmlversion="1.0"encoding="UTF-<web-app" load-on- :配置當前Servlet 中的數(shù)字,表示級別(0-9級),一般設置為0即可 <<<TomcatServlet實url-pattern的三種配在web.xml配置文件中配置有關Servlet的時候，<url-pattern>是用于配置當前Servlet的路徑，也就是說，客戶端瀏覽器<url-pattern>配置的路徑才能對應Servlet內(nèi)容。關于路徑的配置方式其實有三種方式*問路徑為匹配：是以“/”開始，以“/*”結尾的，例如：/firstServlet/*，表示路徑路徑下任意內(nèi)容。以多個不同路徑的。上述三種配置路徑方式具有優(yōu)先級：完全路徑匹配-> 匹配->擴展名匹配。Servlet1Servlet2Servlet3Servlet4/abca.html/abc/*/abc/*”和“/abc/*”和“/*”和“/*”和“如果客戶端瀏覽器請求的路徑是錯誤時，頁面會顯示404錯誤內(nèi)容。這是因為所有發(fā)布到Tomcat服務器的Web應用程序的web.xmlTomcat服務器安裝中conf中的web.xml文 相對路徑與絕對路個頁面來Servlet應該怎么樣呢？下面我們來看一看：在Web工程中的WebRoot “html， 新的HTML頁面。<!DOCTYPE<!DOCTYPEHTMLPUBLIC"-//W3C//DTDHTML4.01<metahttp-equiv=" <metahttp-equiv="description"content="thisismy<metahttp-equiv="content-type"content="text/html;<h1>相對路 <ahref="">相對路徑<h1>絕對路徑<ahref="">絕對路徑在Web工程中的 下，創(chuàng)建一個新的HTML頁面<!DOCTYPE<!DOCTYPEHTMLPUBLIC"-//W3C//DTDHTML4.01<metahttp-"<metahttp-equiv="description"content="thisismy<metahttp-equiv="content-type"content="text/html;<h1>相對路 <ahref="">相對路 <h1>絕對路 <ahref="">絕對路 WebServletpublicpublicclassPathServletextendsHttpServletpublicvoiddoGet(HttpServletRequestrequest,HttpServletResponseresponse)throwsServletException,IOException{到}publicvoiddoPost(HttpServletRequestrequest,HttpServletResponseresponse)throwsServletException,IOException{doGet(request,}}Webweb.xml<?<?xmlversion="1.0"encoding="UTF-<web-app" <<<打開瀏覽器，分別01.html、02.html和PathServlet 01.html的路徑：servlet/html/01.html。 02.html的路徑：servlet/02.html。 PathServlet的路徑：servlet/pathServlet。根據(jù)上述的路徑，可以知道在01.html和02.html頁面中，通過絕對路徑在01.html和02.html頁面中，通過相對路徑PathServlet是不同的在01.html頁面中利用相對路徑PathServlet應該是../pathServlet。原因是是在01.html頁面的父 中<!DOCTYPE<!DOCTYPEHTMLPUBLIC"-//W3C//DTDHTML4.01<metahttp-equiv=" <metahttp-equiv="description"content="thisismy<metahttp-equiv="content-type"content="text/html;<h1>相對路徑<ahref="../pathServlet">相對路徑<h1>絕對路 <<a">在01.html頁面中利用相對路徑PathServlet應該是./pathServlet或直接名pathServlet。原因是pathServlet與02.html頁面處在同一級別 中<!DOCTYPE<!DOCTYPEHTMLPUBLIC"-//W3C//DTDHTML4.01<metahttp-equiv=" <metahttp-equiv="description"content="thisismy<metahttp-equiv="content-type"content="text/html;<h1>相對路徑<ahref="pathServlet">相對路 <h1>絕對路徑<h1>絕對路<a">絕對路絕對路徑：就是無論當前資源在什么位置，都能通過當前資源到目標資源相對路徑：就是判斷當前資源與目標資源的相對位置，找出相對當前資源可以到目標資研究掌HttpServlet概在大多數(shù)的Web應用程序中，客戶端都是通過Http協(xié)議去服務器端的資源，而我們編寫的司在javax.servlet.http包中提供了一個抽象類HttpServlet，它繼承于GenericServlet，用于創(chuàng)建適合基HttpWebServlet。 classHttpServletextendsGenericServletHttpServletMethod req, req, Calledbytheserver(viatheservicemethod)toallowaservlettohandleaGET req, ReceivesanHTTPHEADrequestfromtheprotectedservicemethodandhandles req, Calledbytheserver(viatheservicemethod)toallowaservlettohandlea req, Calledbytheserver(viatheservicemethod)toallowaservlettohandleaPOST req, Calledbytheserver(viatheservicemethod)toallowaservlettohandleaPUT req, Calledbytheserver(viatheservicemethod)toallowaservlettohandleaTRACE ReturnsthetimetheHttpServletRequestobjectwaslastmodified,inmillisecondssincemidnightJanuary1,1970GMT. req, ReceivesstandardHTTPrequestsfromthepublicservicemethodanddispatchesthemtothedoXXXmethodsdefinedinthisclass. req, requeststotheprotectedserviceHttpServlet重寫的service()方HttpServletservice() classHttpServletextendsGenericServlet{publicvoidservice(ServletRequestreq,ServletResponseres)throwsServletException,IOException{HttpServletRequestrequest;HttpServletResponsetryrequest=(HttpServletRequest)req;response=(HttpServletResponse)res;}catch(ClassCastExceptione)thrownewServletException("non-HTTPrequestor}service(request,}protectedvoidservice(HttpServletRequestreq,HttpServletResponseresp)throwsServletException,IOException{Stringmethod=if(method.equals(METHOD_GET))longlastModified=getLastModified(req);maybeSetLastModified(resp,lastModified);doGet(req,resp);}elseif(method.equals(METHOD_HEAD)){longlastModified=getLastModified(req);maybeSetLastModified(resp,lastModified);doHead(req,resp);}elseif(method.equals(METHOD_POST)){doPost(req,resp);}elseif(method.equals(METHOD_PUT)){doPut(req,resp);}elseif(method.equals(METHOD_DELETE)){doDelete(req,resp);}elseif(method.equals(METHOD_OPTIONS)){}}elseif(method.equals(METHOD_TRACE)){}elseStringerrMsgObject[]errArgs=newObject[1];errArgs[0]=method;errMsg=MessageFormat.format(errMsg,errArgs);}}}通過查看HttpServletservice()方法是GenericServlet類中的service()方法，對客戶端的請求進行處理。在第二個service()針對Http1.1協(xié)議中定義的7種請求方式GetPostHeadPutDelete、TraceOptions7種處理方法。7HttpServlet類中的service()ServletHttpServlet對象的請求時，調用該對service()HttpServletRequestHttpServletResponse，然后service()方法。service()Http請求方法的名字，然后根據(jù)請求方法的類型，調用響doXXX()方法。因此，我們在自定義Servlet繼承于HttpServlet的時候，通常不需要重寫service()方法，只需重寫doXXX()方法即可。七種請求處理方HttpServletHttp1.17Get、Post、Head、Put、Delete、TraceOptions7種處理方法：protectedvoiddoGet(HttpServletRequestreq,HttpServletResponseresp)throwsServletException,protectedvoiddoPost(HttpServletRequestreq,HttpServletResponseresp)throwsServletException,protectedvoiddoHead(HttpServletRequestreq,HttpServletResponseresp)throwsServletException,protectedvoiddoPut(HttpServletRequestreq,HttpServletResponseresp)throwsServletException,protectedvoiddoDelete(HttpServletRequestreq,HttpServletResponseresp)throwsServletException,protectedvoiddoTrace(HttpServletRequestreq,HttpServletResponseresp)throwsServletException,protectedvoiddoOptions(HttpServletRequestreq,HttpServletResponseresp)throws要重寫doTrace()和doOptions()方法而對于其他的5種請求處理方法，HttpServlet類提供的實現(xiàn)都是返回Http錯誤。對于Http1.0的客戶端請求，這些方法返回的狀態(tài)碼為400，表示客戶端發(fā)送的請求寫doGet()和doPost()兩個請求處理方法。其中doGet()方法用來處理Get方式的請求，doPost()方法用Post方式的請求，下面我們通過一個案例來看一看：HTML<!DOCTYPEHTMLPUBLIC"-//W3C//DTDHTML4.01<metahttp-equiv="content-type"content="text/html;<h1>GET方式請求<formid="userinfo"method="get"用戶名:<inputtype="textid="username<inputtype="submitid="submitvalue="提交<h1>POST方式請求<formid="userinfo"method="post"用戶名:<inputtype="textid="username<inputtype="submitid="submitvalue="提交ServletpublicpublicclassThreeServletextendsHttpServletpublicvoiddoGet(HttpServletRequestrequest,HttpServletResponseresponse)throwsServletException,IOException{System.out.println("這是GET方式發(fā)送的請求,Servlet使用doGet()方法來理}publicvoiddoPost(HttpServletRequestrequest,HttpServletResponseresponse)throwsServletException,IOException{System.out.println("這是POST方式發(fā)送的請求,Servlet使用doPost()方法來理}}web.xml<?<?xmlversion="1.0"encoding="UTF-<web-app" <<<打開瀏覽器，在地址欄中輸入servlet/index.html利用GET方式發(fā)送請求，控制臺會打印doGet()方法的內(nèi)容。利用POST方式發(fā)送請求，控制臺會doPost()方法的內(nèi)容。RequestHttpServlet提供的service()方法與7HttpServletRequest繼承于ServletRequest，是用于處理Http協(xié)議中的請求，一個是HttpServletResponse繼承于ServletResponseHttp協(xié)議中的響應。HttpServletRequestHttpServletResponse研究掌GenericServlet概如果我們直接通過實現(xiàn)Servlet接口來編寫一個Servlet類，就需要實現(xiàn)Servlet接口定義的5種方Servletjavax.servletGenericServlet，該類提供了除ServletServletServletConfig接口。 classGenericServletimplementsServlet,GenericServletMethodCalledbytheservletcontainertoindicatetoaservletthattheservletisbeingtakenoutgReturnsthisservlet'sServletConfigReturnsareferencetotheServletContextinwhichthisservletisAconveniencemethodwhichcanbeoverriddensothatthere'snoneedto Calledbytheservletcontainertoindicatetoaservletthattheservletisbeingced req, Calledbytheservletcontainertoallowtheservlettorespondtoa重寫的init()方ServletGenericServletGenericServletinit()publicvoidinit(ServletConfigconfig)throwspublicvoidinit()throwstransientinit()方法。GenericServletSerlvetinit()方ServletConfig對javax.servletServletConfig接口。ServletServletConfigServlet初SerlvetWebweb.xmlServlet<?xmlversion="1.0"encoding="UTF-<web-app <description>ThisisthedescriptionofmyJ2EE y-name>Thisisthedis ynameofmyJ2EE GenericServletinit(ServletConfigconfig)ServletConfigpublicpublicclassConfigServletextendsGenericServletprivateServletConfigpublicvoidinit(ServletConfigconfig)throwsServletExceptionthis.config=}publicvoidservice(ServletRequestreq,ServletResponsethrowsServletException,IOException}}ServletConfigServletConfigservletConfig=ServletConfigMethod ReturnsaStringcontainingthevalueofthenamedinitializationparameter,ornulliftheparameterdoesnotexist.Returnsthenamesoftheservlet'sinitializationparametersasanEnumerationStringobjects,oranemptyEnumerationiftheservlethasnoinitializationtReturnsareferencetotheServletContextinwhichthecallerisReturnsthenameofthisservletgetServletName()web.xmlServletServletConfiggetServletName()publicpublicvoidservice(ServletRequestreq,ServletResponsethrowsthrowsServletException,IOException{ServletConfigservletConfig=getServletConfig();StringservletName=servletConfig.getServletName();}ConfigServletnull值。web.xmlServlet<?<?xmlversion="1.0"encoding="UTF-<web-app" Servletservice()publicpublicvoidservice(ServletRequestreq,ServletResponsethrowsServletException,IOException{ServletConfigservletConfig=getServletConfig();Stringname=servletConfig.getInitParameter("name");Stringblog=servletConfig.getInitParameter("blog");System.out.println(name+"'sblogis"+blog);}運行Web應用程序，在控制臺中打印“jyl'sblogis Enumeration是 tor的前身，用法與 tor一致publicpublicvoidservice(ServletRequestreq,ServletResponsethrowsServletException,IOException{ServletConfigservletConfig=getServletConfig();Enumerationenumeration=while(enumeration.hasMoreElements())Stringelement=(String)enumeration.nex Stringvalue=servletConfig.getInitParameter(element);System.out.println(element+":"+value);}}Webname:jylblog:http://wServletConfigstruts1ServletConfig<!--<!--StandardActionServletConfiguration(withdebugging)--<servlet-name>action</servlet-<servlet-class>org.apache.struts.action.ActionServlet</servlet-<init-<param-name>config</param-<param-/WEB-INF/struts-/WEB-INF/struts-config-</param-</init-<load-on-startup>2</load-on-<!--StandardActionServlet --<servlet- <servlet-name>action</servlet-<url-pattern>*.do</url-</servlet- ServletContext對ServletContext概ServletContextServletWebServletContext象，該對象是Web應用程序的全局對象或者上下文。Tomcat服務器在啟動時，會自動創(chuàng)建一個ServletContext對象，ServletContextWeb應用中共享數(shù)據(jù)資源。ServletContextMethod Returnstheservletcontainerattributewiththegivenname,ornullifthereisnoattributebythatname.ReturnsanEnumerationcontainingtheattributenamesavailablewithinthis ReturnsaStringcontainingthevalueofthenamedcontext-wideinitializationparameter,ornulliftheparameterdoesnotexist.Returnsthenamesofthecontext'sinitializationparametersasanEnumerationStringobjects,oranemptyEnumerationifthecontexthasnoinitialization ReturnstheMIMEtypeofthespecifiedfile,ornulliftheMIMEtypeisnot ReturnsaStringcontainingtherealpathforagivenvirtualReturnsthenameofthiswebapplicationcorrespondingtothisServletContextspecifiedinthedeploymentdescriptorforthiswebapplicationbythedisy-nameDeprecated.AsofJavaServletAPI2.1,withnore Writesthespecifiedmessagetoaservletlogfile,usuallyanevent Removestheattributewiththegivennamefromtheservlet name, BindsanobjecttoagivenattributenameinthisservletServletServletContext通過繼承GenericServlet類或HttpServlet類，調用GenericServlet類或HttpServlet類的ServletServletContextpublicpublicclassAServletextendsGenericServlet{publicvoidservice(ServletRequestreq,ServletResponsethrowsServletException,IOException{ServletConfigconfig=getServletConfig();ServletContextcontext1=config.getServletContext();ServletContextcontext2=getServletContext();context2.log("這是通過繼承GenericServlet類獲取到的ServletContext對象}}web.xmlServlet<?<?xmlversion="1.0"encoding="UTF-<web-app" ServletContextlog(Stirngmsg)配置全局初始化參在web.xml<init-param>Servlet是無權限當前Servlet下配置的初始化參數(shù)的。而可以使用ServletContext在web.xml文件中配置全局初始化參數(shù)，這樣當前Web應用程序中的所有Servlet都可以。<?xmlversion="1.0"encoding="UTF-<web-app ServletServletContextpublicpublicclassBServletextendsGenericServlet{publicvoidservice(ServletRequestreq,ServletResponsethrowsServletException,IOException{ServletContextcontext=getServletContext();Stringweixin=context.getInitParameter("weixin");}}打開瀏覽器，在地址欄中分別輸入servlet/servlet/AServlet和servlet/servlet/BServlet，在控制臺打印相關信息。ervltervltCottInitaamerStringe)ervltCottInitaamerName方法獲取所有全局初始化參數(shù)的名稱。ServletContextgetMineType(Stringfile)MIME類publicpublicclassBServletextendsGenericServlet{publicvoidservice(ServletRequestreq,ServletResponsethrowsServletException,IOException{ServletContextcontext=getServletContext();Stringhtml=context.getMimeType("1.html");Stringcss=context.getMimeType("2.css");Stringjavascript=context.getMimeType("3.js");System.out.println("HTML的文件類型為"+html+CSS的文件類型為"+css+",}}HTMLHTML的擴展名為text/htmlCSS的擴展名為text/cssjavascript的擴展名為ServletContext對象的getMineType(Stringfile)方自動Tomcat安 中 中web.xml<?<?xmlversion="1.0"encoding="UTF-<web-app" > Servlet共享數(shù)在同一個Web應用程序中，多個Servlet之間可以共享ServletContext對象中的數(shù)據(jù)信息。主要是通過ServletContext對象的setAttribute(Stringname,Objectobject)方法和getAttribute(Stringname)方法創(chuàng)建一個VisitServlet用來獲取次數(shù)，并在ServletContext對象中publicclassVisitServletextendsHttpServlet{publicvoidinit()throwsServletException{ServletContextcontext=getServletContext();context.setAttribute("times",0);}publicvoiddoGet(HttpServletRequestrequest,HttpServletResponseresponse)throwsServletException,IOException{ServletContextcontext=inttimes=(Integer)context.getAttribute("times");times++;context.setAttribute("times",}publicvoiddoPost(HttpServletRequestrequest,HttpServletResponseresponse)throwsServletException,IOException{doGet(request,}}創(chuàng)建一個ShowTimeServlet用來顯示次數(shù)publicpublicclassShowTimeServletextendsHttpServletpublicvoiddoGet(HttpServletRequestrequest,HttpServletResponseresponse)throwsServletException,IOException{ServletContextcontext=inttimes=PrintWriterout=response.getWriter(); }publicvoiddoPost(HttpServletRequestrequest,HttpServletResponseresponse)throwsServletException,IOException{doGet(request,}}web.xmlSe

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