Block Filter : Filter « Servlets « Java

Block 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.http.HttpServletRequest;

public class BlockFilter implements Filter {

  private FilterConfig config;

  /** Creates new BlockFilter */
  public BlockFilter() {

  public void init(FilterConfig filterConfig) throws ServletException {

    this.config = filterConfig;

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

    HttpServletRequest req = null;
    boolean authenticated = false;
    PrintWriter out = null;

    if (request instanceof HttpServletRequest) {

      req = (HttpServletRequest) request;
      String user = req.getParameter("user");
      authenticated = authenticateUser(user);

    if (authenticated) {
      chain.doFilter(request, response);
    } else {

      out = response.getWriter();
          .println("<html><head><title>Authentication Response</title></head><body>");
      out.println("<h2>Sorry your authentication attempt failed</h2>");


  }// doFilter

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

  private boolean authenticateUser(String userName) {

    //authenticate the user using JNDI and a database, for instance
    return false;



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