I am writing the servlet , in case of exception I am redirecting to my customized error page for that i have done like this.
In web.xml
You're catching the exception, and only printing the stacktrace inside, so the error-page doesn't take affect, remove the try-catch or re-throw and it will work. In addition, you have some syntax errors. Try something like
try{
//Here is all code stuff
throw new Exception();
}catch(Exception e){
e.printStackTrace();
throw new ServletException();
}