res.setBufferSize(8 * 1024); // 8K buffer
res.setContentType("text/html");
PrintWriter out = res.getWriter();
int size = res.getBufferSize(); // returns 8096 or greater
// Record the default size, in the log
log("The default buffer size is " + size);
out.println("The client won't see this");
res.reset();
out.println("Nor will the client see this!");
res.reset();
out.println("And this won't be seen if sendError() is called");
if (req.getParameter("important_parameter") == null) {
res.sendError(res.SC_BAD_REQUEST, "important_parameter needed");
}