简单的一个实现javax.servlet.Filter过滤器实例

package demo;

import java.io.IOException;

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;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/*
 * --------------------DemoFilter演示过滤器的用法----------------------------
 * 统一编码规则
 * 判断用户判断session
 * 选择远程主机ip
 * 过滤非法文字
 */

public class DemoFilter implements Filter {

    public void destroy() {
    // TODO Auto-generated method stub
    System.out.println("Filter销毁...");
    }

    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
    // TODO Auto-generated method stub
    HttpServletRequest res = (HttpServletRequest) request;
    HttpServletResponse rep = (HttpServletResponse) response;
    System.out.println("filter执行...");
    request.setCharacterEncoding("utf-8");
    response.setCharacterEncoding("utf-8");
    String test = request.getParameter("test");
    if (test != null) {
        String anyOneChar="Area";
        if (test.indexOf(anyOneChar) != -1) {
        System.out.println(test + "属于非法字段！！");
        test=test.replaceAll(anyOneChar, "***");
        System.out.println("已经替换为" + test);
       
        } else {
        System.out.println("Filter通过！！");
        }
    }
    HttpSession session = res.getSession();
    if (session.getAttribute("aa") != null) {
        System.out.println("not null");

    } else {
        System.out.println("null");
    }
    String ip = request.getRemoteAddr();
    if (ip.startsWith("127")) {
        System.out.println("你的ip为" + ip + "本来是不可以访问本站哦!!");

    } else {
        System.out.println("continue..");
    }
    chain.doFilter(request, response);

    }

    public void init(FilterConfig filterConfig) throws ServletException {
    // TODO Auto-generated method stub
    System.out.println("Filter初始化...");

    }

}