Having trouble implementing Filter interface for validation

What m doing is.

Whenever a user successfully logs in to my web application its sets the loggedUserType attribute as the student or teacher.

Now i want that some pages should be available to teacher only

so for this m using filters

This is my code for filter

Java Code:

package ankit;
import javax.servlet.Filter;
import javax.servlet.http.*;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

import java.io.IOException;
import javax.servlet.ServletException;

public class SessionCheckFilter implements Filter {

  private String contextPath,userType;

  public void init(FilterConfig fc) throws ServletException {
    contextPath = fc.getServletContext().getContextPath();
  }

  public void doFilter(ServletRequest request, ServletResponse response, FilterChain fc) throws IOException, ServletException {
    HttpServletRequest req = (HttpServletRequest) request;
    HttpServletResponse res = (HttpServletResponse) response;
        userType = String.parseString(req.getSession().getAttribute("loggedUserType"));
    if (req.getSession().getAttribute("loggedUserType") == null) { //checks if there's a loggedUserType set in session...
        res.sendRedirect("http://localhost:8080/vt/index.jsp"); //or page where you want to redirect
    } else {
      System.out.println("Inside Filter="+userType);
      if (!userType.equals("teacher")){ //check if user type is not teacher
        res.sendRedirect("http://localhost:8080/vt/index.jsp"); //or page where you want to
        }
        // This if part is always executed even though the value of userType is teacher.
      fc.doFilter(request, response);
    }
  }

  public void destroy() {
  }
}

This is web.xml file content for filter mapping

Java Code:

<filter>
    <filter-name>SessionCheckFilter</filter-name>
    <filter-class>ankit.SessionCheckFilter</filter-class>
</filter>
<filter-mapping>
    <filter-name>SessionCheckFilter</filter-name>
    <url-pattern>/teacher.jsp</url-pattern> <!-- url from where you implement the filtering -->
</filter-mapping>

i want that only user with loggerUserType attribute as teacher should be allowed to view /teacher.jsp page

but in my case even teacher are being redirected to home page i.e. index.jsp

Whats wrong in my code?

can anyone please help me