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     */  }}