day98-javaweb-context应用

javaweb--servlet的一些应用

servletcontext

简介：当web容器启动的时候，会为每个web容器创建一个对应的servletcontext

代表当前的web应用

功能: 共享数据

setAttribute，将一个数据保存在servletcontext中

 public class HelloServlet extends HttpServlet {
     @Override
     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
         System.out.println("hello");
         ServletContext servletContext = this.getServletContext();
         //web容器启动的时候，会为每个web容器创建一个对应的servletcontext对象
         //代表当前的web应用
         //共享数据
         String username = "gugu";
         servletContext.setAttribute("username",username);
         //将一个数据保存在servletContext中
     }
 }

 

getAttribute,取出保存在servletcontext中的数据

public class GetServlet extends HttpServlet {
     @Override
     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
         ServletContext servletContext = this.getServletContext();
         String username = (String) servletContext.getAttribute("username");
 ​
         resp.setContentType("text/html");
         resp.setCharacterEncoding("utf-8");
         resp.getWriter().print("name: "+username);
     }
 }

 

params，传递相应的参数

首先在web.xml中配置web应用的初始化参数

<!--    配置web应用的初始化参数-->
     <context-param>
         <param-name>url</param-name>
         <param-value>jdbc:mysql://localhost:3306/mybatis</param-value>
     </context-param>

 

读取xml中的对应参数

 public class ServletDemo03_params extends HttpServlet {
     @Override
     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
         ServletContext servletContext = this.getServletContext();
         String url = servletContext.getInitParameter("url");
         resp.getWriter().print(url);
     }
 ​
     @Override
     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
         super.doPost(req, resp);
     }
 }

 

dispatcher,转发请求，可以转发到相应的servlet请求中而保持网址不变

public class ServletDemo04_dispatcher extends HttpServlet {
     @Override
     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
         ServletContext servletContext = this.getServletContext();
         System.out.println("okok");
         RequestDispatcher requestDispatcher = servletContext.getRequestDispatcher("/params");
         //转发的请求路径
         requestDispatcher.forward(req,resp);//调用forward实现请求转发
 ​
         //servletContext.getRequestDispatcher("/hello").forward(req,resp);
 ​
     }
 ​
     @Override
     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
         super.doPost(req, resp);
     }
 }

 

其中可以不设置参数直接调用.forward（）

properties获取properties中的数据

在roperties中编写所需要的数据

 username=root
 password=123456

 

使用InputStream和properties.load读取properties数据为流

 public class ServletDemo05_properties extends HttpServlet {
     @Override
     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
         InputStream resourceAsStream = this.getServletContext().getResourceAsStream("/WEB-INF/classes/db.properties");
         Properties properties = new Properties();
         properties.load(resourceAsStream);
         String username = properties.getProperty("username");
         String password = properties.getProperty("password");
 ​
         resp.getWriter().print(username+password);
 ​
     }
 ​
     @Override
     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
         super.doPost(req, resp);
     }
 }