Already put the code with exception handling.still getting classnotfoundexception? Earlier the code was running fine, but now generating exception

```This register servlet class from where the exception is generating```    
*Earlier the code was running fine on inputting fields in the page.But,after sometime it is generating this exception* 
    
        package com.techblog.servlets;
        
        import java.io.IOException;
        import java.io.PrintWriter;
        
        import javax.servlet.ServletException;
        import javax.servlet.annotation.MultipartConfig;
        import javax.servlet.http.HttpServlet;
        import javax.servlet.http.HttpServletRequest;
        import javax.servlet.http.HttpServletResponse;
        
        import org.apache.jasper.tagplugins.jstl.core.Out;
        
        import com.techblog.dao.Userdao;
        import com.techblog.entities.User;
        import com.techblog.helper.Connectionprovider;
        
        /**
         * Servlet implementation class RegisterServlet
         */
        @MultipartConfig
        public class RegisterServlet extends HttpServlet {
        	
        
        	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        		// TODO Auto-generated method stub
        	String check=request.getParameter("user_check");
        	if(check==null) {
        		System.out.println("Box not checked");
        	}
        	else {
        		String name=request.getParameter("user_name");
        		String email=request.getParameter("user_email");
        		String password=request.getParameter("user_password");
        		String gender=request.getParameter("gender");
        		String about= request.getParameter("about");
        	
        		User user=new User(name,email,password,gender,about);
        		
        		PrintWriter out=response.getWriter();
        		Userdao usd=new Userdao(Connectionprovider.getconnection());
        		if(usd.saveuser(user)) {
        			out.println("done");
        		}
        		else
        		{
        			out.println("Something is wrong");
        		}
        		
        		}
        	    }
                }
>Getting an exception named as classnotfoundexception **SEVERE: Allocate exception for servlet [RegisterServlet]** 

I tried to put the code within try catch also,still not working
package com.techblog.servlets;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.annotation.MultipartConfig;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.jasper.tagplugins.jstl.core.Out;

import com.techblog.dao.Userdao;
import com.techblog.entities.User;
import com.techblog.helper.Connectionprovider;

/**
 * Servlet implementation class RegisterServlet
 */
@MultipartConfig
public class RegisterServlet extends HttpServlet {
	

	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		try {
	String check=request.getParameter("user_check");
	if(check==null) {
		System.out.println("Box not checked");
	}
	else {
		String name=request.getParameter("user_name");
		String email=request.getParameter("user_email");
		String password=request.getParameter("user_password");
		String gender=request.getParameter("gender");
		String about= request.getParameter("about");
	
		User user=new User(name,email,password,gender,about);
		
		PrintWriter out=response.getWriter();
		Userdao usd=new Userdao(Connectionprovider.getconnection());
		if(usd.saveuser(user)) {
			out.println("done");
		}
		else
		{
			out.println("Something is wrong");
		}
		
		}
		}
		catch(Exception e) {
			System.out.println(e);
		}
	}

	
	

}