如何访问servlet上下文侦听器中的属性？

Question

I want to access a attribute that I set up in the context listener from a jsp file. I have set up the servlet listener, then I added the listener into web.xml. My servlet listener will be used to connect to the database.

Here is my context Listener (necessary class are imported):

 @WebServlet("/MyServletContextListener")
  public class MyServletContextListener implements ServletContextListener{

    public void contextDestroyed(ServletContextEvent event) {
        System.out.println("ServletContextListener destroyed");
    }

        //Run this before web application is started
    public void contextInitialized(ServletContextEvent event) {
        System.out.println("ServletContextListener started");   
        String DriverName = "com.mysql.jdbc.Driver";
        String conURL = "jdbc:mysql://localhost/";
        ServletContext context = event.getServletContext();
        String dbName = context.getInitParameter("dbName");
        String user = context.getInitParameter("user");
        String pass = context.getInitParameter("pw");
        Connection conn = null;
        try{
            Class.forName(DriverName);
            conn = DriverManager.getConnection(conURL+dbName, user,pass);
        }catch(ClassNotFoundException ex){

        }catch(SQLException sqle){

        }
        context.setAttribute("conn", conn);
    }
}

From my jsp file I want to access "conn".

This is my xml:

 <web-app>
    <listener>
<listener-class>
    Listener.MyServletContextListener
</listener-class>
</listener>

this is my jsp:

    <%
    ServletContext context = getServletContext();
    context.getAttribute("conn");
    System.out.println(context.getAttribute("conn"));
    boolean loginpass = false;
    String login = request.getParameter("login");
    String pw = request.getParameter("password");
    try {
        loginpass = checklogin(login, pw,
                (java.sql.Connection) context.getAttribute("conn"));
    } catch (java.sql.SQLException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
%>

the line System.out.println(context.getAttribute("conn")) prints out : null

I shouldn't be null, it should be connected to the database. The database password and user name are correct. Database password and user name are in web.xml under context-param . How do I get the conn attribute from MyServletContextListener?

Answer 1

Your connection code may have connection error print the stack trace. so that you will come to know actual problem.

catch(ClassNotFoundException ex){
     System.out.println(ex) 
}
catch(SQLException sqle){
 System.out.println(sqle)
}

Answer 2

Add the mysql connector in the deployment assembly. Project File ->properites -> Deployment Assembly -> add