利用Filter实现IP过滤

import Java.io.IOException;
import java.util.StringTokenizer;

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.HttpServletResponse;

public class IPFilter implements Filter {

  private FilterConfig config;

  public final static String IP_RANGE = "192.168";

  public IPFilter() {
  }

  public void init(FilterConfig filterConfig) throws ServletException {

    this.config = filterConfig;

  }

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

    String ip = request.getRemoteAddr();

    HttpServletResponse httpResp = null;

    if (response instanceof HttpServletResponse)
      httpResp = (HttpServletResponse) response;

    StringTokenizer toke = new StringTokenizer(ip, ".");
    int dots = 0;
    String byte1 = "";
    String byte2 = "";
    String client = "";

    while (toke.hasMoreTokens()) {

      ++dots;

      //if we've reached the second dot, break and check out the indx
      // value
      if (dots == 1) {

        byte1 = toke.nextToken();

      } else {

        byte2 = toke.nextToken();
        break;
      }
    }//while

    //Piece together half of the client IP address so it can be compared
    // with
    //the forbidden range represented by IPFilter.IP_RANGE
    client = byte1 + "." + byte2;

    if (IP_RANGE.equals(client)) {

      httpResp.sendError(HttpServletResponse.SC_FORBIDDEN,
          "That means goodbye forever!");

    } else {

      chain.doFilter(request, response);
    }

  }// doFilter

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

}

（出处：）