前言：

本文内容：ServletContext对象、ServletContext应用

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ServletContext对象

Web容器在启动的时候，它会为每个web程序都创建一个对应的ServletContext对象，它代表了当前的web应用：

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  • 共享数据

    多个Servlet之间可以数据共享

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    public class HelloServlet extends HttpServlet {
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            System.out.println("hello");
            // this.getInitParameter(); 初始化参数
            // this.getServletConfig(); Servlet配置
            // this.getServletContext(); Servlet上下文
            ServletContext context = this.getServletContext();
            String username = "小王";
            // 将数据保存在ServletContext
            context.setAttribute("username",username);
        }

        @Override
        protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            doGet(req,resp);
        }
    }

    读取的Servlet

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    public class GetServlet extends HttpServlet {
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            ServletContext context = this.getServletContext();
            // 获取HelloServlet中传的值
            String username=(String) context.getAttribute("username");
            resp.setContentType("text/html;charset=utf-8");
            resp.getWriter().print("姓名："+username);
        }

        @Override
        protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            doGet(req,resp);
        }
    }

    配置文件

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    <!--    注册Servlet-->
      <servlet>
        <servlet-name>hello</servlet-name>
        <servlet-class>com.jokerdig.servlet.HelloServlet</servlet-class>
      </servlet>
      <!--    Servlet映射-->
      <servlet-mapping>
        <servlet-name>hello</servlet-name>
        <url-pattern>/hello</url-pattern>
      </servlet-mapping>
      <!-- get注册-->
      <servlet>
        <servlet-name>get</servlet-name>
        <servlet-class>com.jokerdig.servlet.GetServlet</servlet-class>
      </servlet>
      <servlet-mapping>
        <servlet-name>get</servlet-name>
        <url-pattern>/get</url-pattern>
      </servlet-mapping>

    测试值结果，Servlet之间通过ServletContext可以传递数据

ServletContext应用

获取初始化参数

配置初始化参数

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

获取初始化参数

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@Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        ServletContext context = this.getServletContext();
        String url = context.getInitParameter("url");
        resp.setContentType("text/html;charset=utf-8");
        resp.getWriter().print(url);
    }

请求转发

请求转发地址不会改变

重定向地址会改变

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@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    ServletContext context = this.getServletContext();
    System.out.println("进入了ServletDemo02");
    resp.setContentType("text/html;charset=utf-8");
    // 转发的请求路径
    RequestDispatcher reqD = context.getRequestDispatcher("/para");
    reqD.forward(req,resp);// 调用forward实现请求转发
}

读取资源文件

Properties

  • 在Java目录下新建Properties
  • 在resources下新建properties

发现：都被打包到了同一个路径下：classes，我们称为类路径

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读取properties资源文件

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@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    ServletContext context = this.getServletContext();
    // 读取properties资源文件
    InputStream is = context.getResourceAsStream("/WEB-INF/classes/db.properties");
    Properties pro = new Properties();
    pro.load(is);
    String user = pro.getProperty("username");
    String pwd = pro.getProperty("password");
    resp.getWriter().print(user+":"+pwd);
}

web.xml配置

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<!--    注册Servlet-->
<servlet>
  <servlet-name>pro</servlet-name>
  <servlet-class>com.jokerdig.servlet.PropertiesServlet</servlet-class>
</servlet>
<servlet-mapping>
  <servlet-name>pro</servlet-name>
  <url-pattern>/pro</url-pattern>
</servlet-mapping>