前言：

　　在一些业务需求中有的是只能当前主机登录熊系统，或者说是当前的网段内用户可以访问，这时候就需要用到了servlet中的过滤器了。

放行指定IP：

编写过滤器：　　

package com.mixky.app.bjcc.filter;

import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import java.io.IOException;
import java.io.PrintWriter;
import java.io.UnsupportedEncodingException;

/**
 * @author zhangzhixi
 * @version 1.0
 * @date 2021-8-16 16:38
 */
public class NoteFilter implements Filter {

    private FilterConfig config = null;

    //ip白名单
    private String ipTable = null;


    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("note filter initial");
        this.config = filterConfig;
        /*获取白名单*/
        this.ipTable = config.getInitParameter("ipTable");
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        System.out.println("do filter starting");

        /*校验ip地址：不是白名单就直接结束*/
        if (!verifyIP(request, response)) {
            return;
        }

        long befor = System.currentTimeMillis();
        config.getServletContext().log("before call note Filter");

        chain.doFilter(request, response);

        config.getServletContext().log("after call note Filter");
        long after = System.currentTimeMillis();

        String name = "";
        if (request instanceof HttpServletRequest) {
            name = ((HttpServletRequest) request).getRequestURI();
        }
        config.getServletContext().log("Note Filter : name:" + name + " time :" + (after - befor) + "ms");
    }

    @Override
    public void destroy() {

    }

    /**
     * 验证IP
     *
     * @param request  请求
     * @param response 响应
     * @return 校验结果
     */
    private boolean verifyIP(ServletRequest request, ServletResponse response) {
        /*获取本机IP地址*/
        String ip = request.getLocalAddr();

        /*windows下本机测试*/
        if ("0:0:0:0:0:0:0:1".equals(ip)) {
            ip = "127.0.0.1";
            System.out.println("请求ip:" + ip);
        }
        System.out.println("本机IP是：" + ip);
        System.out.println("ipTable白名单:" + ipTable);
        /*是白名单用户*/
        if (ipTable.equals(ip)) {
            return true;
        } else {
            System.out.println("校验不通过");
            /*设置编码*/
            try {
                request.setCharacterEncoding("UTF-8");
                response.setContentType("text/html;charset=UTF-8");
                PrintWriter out = null;
                try {
                    out = response.getWriter();
                    out.print("<h1>对不起，你的ip不能访问服务器</h1>");
                    out.flush();
                    out.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            } catch (UnsupportedEncodingException e) {
                e.printStackTrace();
            }
            return false;
        }
    }
}

web.xml配置文件：

<!--IP过滤-->
<filter>
	<filter-name>ip</filter-name>
	<filter-class>com.mixky.app.bjcc.filter.NoteFilter</filter-class>
	<init-param>
		<param-name>ipTable</param-name>
		<!--设置的白名单IP-->
		<param-value>127.0.0.1</param-value>
	</init-param>
</filter>
<filter-mapping>
	<filter-name>ip</filter-name>
	<!--过滤所有请求-->
	<url-pattern>/*</url-pattern>
</filter-mapping>