标签:统计 应用 post value pac 信息 通用 文件 rac
ServletContext类似字节码文件对象,在web创建的时候就自动生成了,并且是唯一的,跟随着项目和服务器共存亡了。通过这个对象,我们可以向里面存数据(键值对),也可以通过别的Servlet来获取这个数据;也可以根据相对(服务器)路径继来获取绝对路径。根据这个信息我们可以在以后创建文件的过程中,将静态资源的文件尽量创建在web-content文件夹下,而项目文件、配置文件创建在src下。不要直接创建在web文件夹下(不会在服务器上生成)。
一、ServletContext对象:
ServletContext代表是一个web应用的环境(上下文)对象,ServletContext对象内部封装是该web应用的信息,ServletContext对象一个web应用只有一个。
二、ServletContext对象的生命周期:
创建:该web应用被加载且服务器开启时创建;
销毁:web应用被卸载(移除该项目应用)或者服务器关闭。
三、获得ServletContext对象:
1、Servlet的init方法中获得ServletConfig
ServletContext servletContext = config.getServletContext ()
2、
ServletContext servletContext = this.getservletContext ()
四、ServletContext的作用:
1、获得web应用全局的初始化参数;
2、获得web应用中任何资源的绝对路径:
(通过服务器的相对路径,得到一个在服务器上的绝对路径)
String path = context.getRealPath(相对于该web应用的相对地址);
package com.oracle.web; import java.io.IOException; import javax.servlet.ServletConfig; import javax.servlet.ServletContext; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public class Servlet extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //获取ServletContext对象 ServletContext context=getServletConfig().getServletContext(); /*//1.获取ServletConfig对象 ServletConfig config=getServletConfig(); //2.获取ServletContext对象 ServletContext context=config.getServletContext();*/ //获取相对路径的绝对路径 String patha=context.getRealPath("a.txt"); System.out.println(patha); String pathb=context.getRealPath("WEB-INF/b.txt"); System.out.println(pathb); String pathc=context.getRealPath("WEB-INF/classes/c.txt"); System.out.println(pathc); response.getWriter().write("hello dandan..."); } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); } }
3、ServletContext是一个域对象(存储数据的区域):
ServletContext域对象的作用范围:整个web
(所有的web资源都可以随意向 ServletContext 域中存取数据,数据可以分享)。
域对象的通用方法:
package com.oracle.web; import java.io.IOException; import javax.servlet.ServletContext; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public class Servlet03 extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //hqServletContextdx ServletContext context=getServletContext(); //取值 String value=(String)context.getAttribute("name"); response.getWriter().write(value); } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); } }package com.oracle.web; import java.io.IOException; import javax.servlet.ServletContext; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public class Servlet02 extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //hqServletContextdx ServletContext context=getServletContext(); //存值 context.setAttribute("name","zhangsan"); } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); } }
登录统计:
package com.oracle.web; import java.io.IOException; import javax.servlet.ServletContext; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import com.oracle.service.UserService; public class LoginServlet extends HttpServlet { private UserService userService=new UserService(); @Override public void init() throws ServletException { int num=0; //获取ServletContextdx ServletContext context=getServletContext(); context.setAttribute("num", num); } public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //获取用户名和密码 String name=request.getParameter("username"); System.out.println(name); String pwd=request.getParameter("pwd"); //调用service层方法 int count=userService.login(name, pwd); if (count>0) { //获取ServletContextdx ServletContext context=getServletContext(); int num=(int)context.getAttribute("num"); num++; context.setAttribute("num", num); response.getWriter().write("you are the "+num+"success"); }else { response.getWriter().write("fail"); } } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); } }
标签:统计 应用 post value pac 信息 通用 文件 rac
原文地址:https://www.cnblogs.com/zqy6666/p/12356869.html