Filter设计实现IP地址限制

示例：创建一个IP过滤Filter，当一个用户发出访问请求的时候，首先通过过滤器进行判断，

如果用户的IP地址被限制，就禁止访问，只有合法的IP才可以继续访问。IP过滤Filter代码如下：

IPFilter.java

 package com.mhb;

 import java.io.IOException;
 import java.io.PrintWriter;

 import javax.servlet.Filter;
 import javax.servlet.FilterChain;
 import javax.servlet.FilterConfig;
 import javax.servlet.ServletException;
 import javax.servlet.ServletRequest;
 import javax.servlet.ServletResponse;

 public class IPFilter implements Filter {

 protected FilterConfig filterConfig;
 protected String ip;

 public void init(FilterConfig filterConfig) throws ServletException {
 this.filterConfig = filterConfig;    //设置属性filterConfig
 this.ip = this.filterConfig.getInitParameter("ip");    //设置初始化参数IP
 }
 //过滤方法
 public void doFilter(ServletRequest request, ServletResponse response,
 FilterChain chain) throws IOException, ServletException {
 String remoteIP = request.getLocalAddr();    //获得客户端ip地址

 if(remoteIP.equals(ip)){    //判断IP是否被禁止
 response.setCharacterEncoding("gb2312");    //设置输出内容编码格式
 PrintWriter out = response.getWriter();
 out.println("<b>你的IP地址被禁止访问！</b>");
 }else{
 chain.doFilter(request, response);
 }
 }
 //销毁方法
 public void destroy() {
 }
 }

web.xml配置

 <filter>
      <filter-name>IPFilter</filter-name>
      <filter-class>com.mhb.IPFilter</filter-class>
      <init-param>
       <param-name>ip</param-name>
       <param-value>127.0.0.1</param-value>
      </init-param>
  </filter>
  <filter-mapping>
       <filter-name>IPFilter</filter-name>
       <url-pattern>/*</url-pattern>
  </filter-mapping>
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
</web-app>

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