hi i have the same problem 
can you help please

this is my code:
 
@SuppressWarnings("serial")
@WebServlet(urlPatterns = {"/LogIn"})
public class LogIn extends HttpServlet {

    @Override
    public void doPost(HttpServletRequest request, HttpServletResponse response) 
        throws IOException {
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        User signedInUser = User.login(username, password);

        if(!signedInUser.equals(null)){
        	 HttpSession s = request.getSession();
             s.setAttribute("signedInKey", (new Date()).getTime() + (new Random()).nextInt(999999999));
             request.setAttribute("user", signedInUser);
             String url = "http://localhost:8080/java_project/test.jsp";
             response.sendRedirect(url);
        }
        
        String url = "http://localhost:8080/java_project/notLogIn.jsp";
        response.sendRedirect(url);
    }
    
}




and this is the error:



HTTP Status 500 - Servlet execution threw an exception

--------------------------------------------------------------------------------

type Exception report

message Servlet execution threw an exception

description The server encountered an internal error that prevented it from fulfilling this request.

exception 

javax.servlet.ServletException: Servlet execution threw an exception


root cause 

java.lang.NoClassDefFoundError: org/hibernate/Session
	ir.ac.shirazu.cse.LogIn.doPost(LogIn.java:25)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:728)


root cause 

java.lang.ClassNotFoundException: org.hibernate.Session
	org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1714)
	org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1559)
	ir.ac.shirazu.cse.LogIn.doPost(LogIn.java:25)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:728)


note The full stack trace of the root cause is available in the Apache Tomcat/7.0.40 logs.


--------------------------------------------------------------------------------

Apache Tomcat/7.0.40