why it is not working?

Question

if((x.getParameter("Amount")).trim().isEmpty())
{
y.sendRedirect("invalid.jsp");
// pw.print(d);
}

Answer 1

before (x.getP... and after ..."Amount") the second bracket is not needed
it should be:
if (x.getParameter("Amount").trim().isEmpty()) { ... }

for further help I have to know what datatype x and y are!