java code for Checker Filter

import java.io.IOException;
import java.util.Enumeration;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

public class CheckFilter implements Filter {

private FilterConfig config;

public CheckFilter() {
}

public void init(FilterConfig filterConfig) throws ServletException {

this.config = filterConfig;

}

public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {

Enumeration params = request.getParameterNames();
boolean rejected = false;

while (params.hasMoreElements()) {

if (isEmpty(request.getParameter((String) params.nextElement()))) {
reject(request, response);
rejected = true;
}

}

if (!rejected)
chain.doFilter(request, response);

}// doFilter

private boolean isEmpty(String param) {

if (param == null || param.length() < 1) {
return true;
}

return false;

}

private void reject(ServletRequest request, ServletResponse response)
throws IOException, ServletException {

request.setAttribute("errorMsg",
"Please make sure to provide a valid value for all of the text fields.");

Enumeration params = request.getParameterNames();
String paramN = null;

while (params.hasMoreElements()) {

paramN = (String) params.nextElement();

request.setAttribute(paramN, request.getParameter(paramN));

}

RequestDispatcher dispatcher = request
.getRequestDispatcher("/form.jsp");
dispatcher.forward(request, response);

}

public void destroy() {
/*
* called before the Filter instance is removed from service by the web
* container
*/
}

}