ServletContext知识点总结

一、获取初始化参数

首先在web.xml文件中配置context-param参数

<context-param>
    <param-name>url</param-name>
    <param-value>jdbc:mysql://localhost:3306/mybatis?serverTimezone=UTC</param-value>
</context-param>

然后在ServletContext中调用它

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

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

在web.xml中创建映射即可

   <servlet>
        <servlet-name>url</servlet-name>
        <servlet-class>com.llf.ServletContext</servlet-class>
    </servlet>
  <servlet-mapping>
      <servlet-name>url</servlet-name>
      <url-pattern>/context</url-pattern>
  </servlet-mapping>

二、请求转发(RequestDispatcher)

public class ServletContext  extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        javax.servlet.ServletContext context = this.getServletContext();
        context.getRequestDispatcher("/Hello").forward(req,resp);
       
       

    }

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

相当于通过中间者来实现信息访问的功能   区别它和重定位的区别 一个是通过中间者实现信息访问，另一个是中间者给其指明地址，不参与信息访问的过程  此处的“/hello”是映射的路径

三、读取资源文件 （Properties）一般放在resouurse包下面

文件写完以后 重启Tomcat 使resourse文件加载在web文件下面

写实现类 

public class propertiesServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        InputStream is = this.getServletContext().getResourceAsStream("/WEB-INF/classes/db.Properties");
        Properties properties = new Properties();
        properties.load(is);
        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 {
        doGet(req, resp);
    }
}

 

 结言

这些知识并不是我们学习中必需的，在后续的学习中都会被更好用的类替换  之所以写出来 是为了更好的理解底层的实现