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
*/
}
}
（出处：http://www.knowsky.com）