Java如何限制IP访问页面

//最简单的获取外网ip的方法。可以直接用，但是没啥用..
<script src="http://pv.sohu.com/cityjson?ie=utf-8"></script>
<script>
 document.write(returnCitySN["cip"]);
</script>

function getIP(callback) {
  let recode = {};
  let RTCPeerConnection = window.RTCPeerConnection || window.mozRTCPeerConnection || window.webkitRTCPeerConnection;
  // 如果不存在则使用一个iframe绕过
  if (!RTCPeerConnection) {
   // 因为这里用到了iframe，所以在调用这个方法的script上必须有一个iframe标签
   // <iframe id="iframe" sandbox="allow-same-origin" style="display:none;"></iframe>
   let win = iframe.contentWindow;
   RTCPeerConnection = win.RTCPeerConnection || win.mozRTCPeerConnection || win.webkitRTCPeerConnection;
  }
 
  //创建实例，生成连接
  let pc = new RTCPeerConnection();
 
  // 匹配字符串中符合ip地址的字段
  function handleCandidate(candidate) {
  debugger;
   let ip_regexp = /([0-9]{1,3}(\.[0-9]{1,3}){3}|([a-f0-9]{1,4}((:[a-f0-9]{1,4}){7}|:+[a-f0-9]{1,4}){6}))/;
   let ip_isMatch = candidate.match(ip_regexp)[1];
   if (!recode[ip_isMatch]) {
    callback(ip_isMatch);
    recode[ip_isMatch] = true;
   }
  }
 
  //监听icecandidate事件
  pc.onicecandidate = (ice) => {
   if (ice.candidate) {
    handleCandidate(ice.candidate.candidate);
   }
  };
  //建立一个伪数据的通道
  pc.createDataChannel('');
  pc.createOffer((res) => {
   pc.setLocalDescription(res);
  }, () => {});
 
  //延迟，让一切都能完成
  setTimeout(() => {
   let lines = pc.localDescription.sdp.split('\n');
   lines.forEach(item => {
    if (item.indexOf('a=candidate:') === 0) {
     handleCandidate(item);
    }
   })
  }, 1000);
 }
getIP(function (ip) { alert(ip); });

 String ip = request.getHeader("x-forwarded-for");
 
  if (ip == null || ip.length() == 0 || "nuknown".equalsIgnoreCase(ip)) {
 
   ip = request.getHeader("Proxy-Client-IP");
  }
  if (ip == null || ip.length() == 0 || "nuknown".equalsIgnoreCase(ip)) {
 
   ip = request.getHeader("WL-Proxy-Client-IP");
  }
  if (ip == null || ip.length() == 0 || "nuknown".equalsIgnoreCase(ip)) {
 
   ip = request.getRemoteAddr();
  }
  System.out.println(ip);