The following example show you how to create a servlet filter using the @WebFilter annotation. We will create a simple filter that will check whether an attribute is exists in the http session object. If no attribute found this filter will redirect user into a login page.
package org.kodejava.example.filter;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
@WebFilter(urlPatterns = {"/*"}, description = "Session Checker Filter")
public class SessionCheckerFilter implements Filter {
private FilterConfig config = null;
public void init(FilterConfig config) throws ServletException {
this.config = config;
config.getServletContext().log("Initializing SessionCheckerFilter");
}
public void doFilter(ServletRequest req, ServletResponse res,
FilterChain chain)
throws ServletException, IOException {
HttpServletRequest request = (HttpServletRequest) req;
HttpServletResponse response = (HttpServletResponse) res;
//
// Check to see if user's session attribute contains an attribute
// named AUTHENTICATED. If the attribute is not exists redirect
// user to the login page.
//
if (!request.getRequestURI().endsWith("login.jsp") &&
request.getSession().getAttribute("AUTHENTICATED") == null) {
response.sendRedirect(request.getContextPath() + "/login.jsp");
}
chain.doFilter(req, res);
}
public void destroy() {
config.getServletContext().log("Destroying SessionCheckerFilter");
}
}
Before the birth of @WebFilter annotation as defined in the Servlet 3.0 Specification. To make the filter functional we must register it in the web.xml file by using the filter and the filter-mapping element. And once it active it will collaborate with the other filters in the filter chain for the current servlet context.
