jsp的appilication.getInitParameter()方法无法获取到值的问题

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
         version="3.1">
    <!--配置第一个参数：数据驱动名称-->
    <context-param>
        <param-name>driver</param-name>
        <param-value>com.mysql.jdbc.Driver</param-value>
    </context-param>
    <!--数据库的url-->
    <context-param>
        <param-name>url</param-name>
        <param-value>jdbc:mysql://localhost:3306/keyan</param-value>
    </context-param>
    <!--配置第二个参数:用户名-->
    <context-param>
        <param-name>usr</param-name>
        <param-value>root</param-value>
    </context-param>
    <!--配置第三个参数：密码-->
    <context-param>
        <param-name>passwd</param-name>
        <param-value>root</param-value>
    </context-param>
</web-app>

<%
    String driver = application.getInitParameter("driver");
    String url = application.getInitParameter("url");
    String usr = application.getInitParameter("usr");
    String passwd = application.getInitParameter("passwd");
    /*注册驱动*/
    //driver = "com.mysql.jdbc.Driver";
    Class.forName(driver);
    //开始链接
    Connection connection = DriverManager.getConnection(url,usr,passwd);
    //创建查询语句
    Statement statement = connection.createStatement();
    //sql语句
    String sql = "select * from e_person";
    //开始执行
    ResultSet set = statement.executeQuery(sql);
%>
<table border="1" bgcolor="blue" width="300px">
    <%
        while(set.next()){

    %>
    <tr>
        <td><%set.getString(1);%></td>
        <td><%set.getString(2);%></td>
    </tr>
    <%
        }
    %>

</table>