ServletContext的使用
ServletContext:
ServletContext表示Servlet应用程序。每个Web应用程序只有一个上下文。在将一个应用程序同时部署到多个容器的分布式环境中,每台Java虚拟机上的Web应用都会有一个ServletContext对象。
通过在ServletConfig中调用getServletContext方法,可以获得ServletContext。
有了ServletContext,就可以共享从应用程序中的所有资料处访问到的信息,并且可以动态注册Web对象。前者将对象保存到ServletContext中的一个内部的Map中。保存在ServletContext中的对象被称作属性。
1:实现数据共享 setAttribute(key,value) getAttribute(key) ,获取域对象
2:获取全局配置信息: getInitParameter()
3:获得应用下任何资源的路径
例一:通过调用GenericServlet的 getServletContext对象得到ServletContext对象,获取域对象
先运行myservlet1.java,在运行myservlet2.java
myservlet1.java
1 2 3 4 5 6 7 8 9 10 11 12 13 14 | public class myservlet extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //通过调用GenericServlet的 getServletContext对象得到ServletContext对象 //先访问demo1,在访问demo2 ServletContext application= this .getServletContext(); application.setAttribute( "name" , "tom" ); System.out.println(application.getClass().getName()); } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request,response); } } |
myservlet2.java
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 | public class myservlet2 extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String name=(String) this .getServletContext().getAttribute( "name" ); if (name== null ){ System.out.println( "你不能直接访问这个类" ); } System.out.println(name); } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request,response); } } |
运行效果图:
例二:获取全局配置信息
获取encoding的配置信息
myservlet3.java
1 2 3 4 5 6 7 8 9 10 11 | public class myservlet3 extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String encoding= this .getServletContext().getInitParameter( "encoding" ); System.out.println(encoding); } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request,response); } } |
web.xml
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 | <?xml version= "1.0" encoding= "UTF-8" ?> <web-app version= "2.5" xmlns= "http://java.sun.com/xml/ns/javaee" xmlns:xsi= "http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http: //java.sun.com/xml/ns/javaee http: //java.sun.com/xml/ns/javaee/web-app_2_5.xsd"> <display-name></display-name> <context-param> <param-name>encoding</param-name> <param-value>utf- 8 </param-value> </context-param> <servlet> <servlet-name>myservlet</servlet-name> <servlet- class >com.zk.myservlet.myservlet</servlet- class > </servlet> <servlet> <servlet-name>myservlet2</servlet-name> <servlet- class >com.zk.myservlet.myservlet2</servlet- class > </servlet> <servlet> <servlet-name>myservlet3</servlet-name> <servlet- class >com.zk.myservlet.myservlet3</servlet- class > </servlet> <servlet-mapping> <servlet-name>myservlet</servlet-name> <url-pattern>/demo1</url-pattern> </servlet-mapping> <servlet-mapping> <servlet-name>myservlet2</servlet-name> <url-pattern>/demo2</url-pattern> </servlet-mapping> <servlet-mapping> <servlet-name>myservlet3</servlet-name> <url-pattern>/demo3</url-pattern> </servlet-mapping> <welcome-file-list> <welcome-file>index.jsp</welcome-file> </welcome-file-list> </web-app> |
例三:获取资源路径
使用this.getServletContext().getRealPath获取文件的资源路径
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 | public class myservlet1 extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String apath= this .getServletContext().getRealPath( "/WEB-INF/a.properties" ); //参数一定要以斜杠开头 System.out.println(apath); //创建一个properties Properties pro= new Properties(); pro.load( new FileInputStream(apath)); System.out.println(pro.getProperty( "akey" )); String bpath= this .getServletContext().getRealPath( "/WEB-INF/classes/b.properties" ); System.out.println(bpath); Properties pro2= new Properties(); pro2.load( new FileInputStream(bpath)); System.out.println(pro2.getProperty( "key" )); String cpath= this .getServletContext().getRealPath( "/WEB-INF/classes/com/zk/myservlet/c.properties" ); System.out.println(cpath); Properties pro3= new Properties(); pro3.load( new FileInputStream(cpath)); System.out.println(pro3.get( "ckey" )); } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request,response); } } |
运行结果图:
【推荐】编程新体验,更懂你的AI,立即体验豆包MarsCode编程助手
【推荐】凌霞软件回馈社区,博客园 & 1Panel & Halo 联合会员上线
【推荐】抖音旗下AI助手豆包,你的智能百科全书,全免费不限次数
【推荐】轻量又高性能的 SSH 工具 IShell:AI 加持,快人一步