IP查找所属网段

最近同学接到阿里面试题

 package io.guangsoft.analysis;

 /*
      数据文件:
     1.1.1.0/24,123
     1.1.2.0/28,345
     1.2.0.0/16,789
  */
 public interface Finder {
     //完成初始化动作
     boolean loadFile(String fileName);
     //查找具体IP所在IP网段的键值，未找到返回-1；比如如果输入样例数据文件，调用find("1,1,1,1"),返回123
     int find(String ipStr);
 }

搜索一番解答如下

 package io.guangsoft.analysis;

 import java.io.BufferedReader;
 import java.io.File;
 import java.io.FileReader;
 import java.util.HashMap;
 import java.util.Map;

 import org.apache.commons.net.util.SubnetUtils;
 import org.apache.commons.net.util.SubnetUtils.SubnetInfo;

 public class FinderImpl implements Finder {

     private Map<String, String> dataMap = new HashMap<String, String>();

     @Override
     public boolean loadFile(String fileName) {
         File file = new File(this.getClass().getClassLoader().getResource(fileName).getFile());
         try {
             FileReader fileReader = new FileReader(file);
             BufferedReader bufferedReader = new BufferedReader(fileReader);
             while(true) {
                 String nextLine = bufferedReader.readLine();
                 if(nextLine == null) {
                     break;
                 } else {
                     String str[] = nextLine.split(",");
                     dataMap.put(str[0], str[1]);
                 }
             }
         } catch (Exception e) {
             e.printStackTrace();
             return false;
         }
         return true;
     }

     @Override
     public int find(String ip) {
         for(String network : dataMap.keySet()) {
             boolean bingo = isInRange(ip, network);
             if(bingo) {
                 return Integer.parseInt(dataMap.get(network));
             }
         }
         return -1;
     }

     //核心代码，检索IP所属网段
     public boolean isInRange(String ip, String network) {
         String[] ips = ip.split("\\.");
         int ipAddr = (Integer.parseInt(ips[0]) << 24)
                 | (Integer.parseInt(ips[1]) << 16)
                 | (Integer.parseInt(ips[2]) << 8)
                 | Integer.parseInt(ips[3]);
         int type = Integer.parseInt(network.replaceAll(".*/", ""));
         int mask = 0xFFFFFFFF << (32 - type);
         String networkIp = network.replaceAll("/.*", "");
         String[] networkIps = networkIp.split("\\.");
         int networkIpAddr = (Integer.parseInt(networkIps[0]) << 24)
                 | (Integer.parseInt(networkIps[1]) << 16)
                 | (Integer.parseInt(networkIps[2]) << 8)
                 | Integer.parseInt(networkIps[3]);
          return (ipAddr & mask) == (networkIpAddr & mask);
     }

     //也可以使用apache的net工具类
     public boolean isInRange2(String ip, String network) {
         SubnetInfo subnetInfo = new SubnetUtils(network).getInfo();
         return subnetInfo.isInRange(ip);
     }

     public static void main(String args[]) {
         FinderImpl finder = new FinderImpl();
         if(finder.loadFile("data.txt")) {
             int num = finder.find("1.1.1.1");
             System.out.println(num);
         }
     }

 }