throwing an unknown exception in java web application

Question

I'm trying to create a web application. While inserting into token table for login, it throws an exception and I can't figure out the reason it prints "catch Invalid"

protected void processRequest(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {
    response.setContentType("text/html;charset=UTF-8");
    request.setCharacterEncoding("UTF-8");
    String email=request.getParameter("email");
    String password=request.getParameter("password");
    byte[]passwordBytes=password.getBytes();
    PrintWriter writer=response.getWriter();

    try {
       MessageDigest messageDigest=MessageDigest.getInstance("MD5");
        byte[]hashBytes=messageDigest.digest(passwordBytes);
        String hash=new String (hashBytes);
        DatabaseHelper helper=new DatabaseHelper();
        String token=helper.signin(email,hash);

        if(token!=null){
             writer.print(token);
        }
         else{
             writer.print("Invalid");
           }
    } catch (Exception e) {
        writer.print("catch invalid");
    }


}