最近同学接到阿里面试题

1 package io.guangsoft.analysis; 2  3 /* 4      数据文件: 5     1.1.1.0/24,123 6     1.1.2.0/28,345 7     1.2.0.0/16,789  8  */ 9 public interface Finder {10     //完成初始化动作11     boolean loadFile(String fileName);12     //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12313     int find(String ipStr); 14 }

搜索一番解答如下

1 package io.guangsoft.analysis; 2  3 import java.io.BufferedReader; 4 import java.io.File; 5 import java.io.FileReader; 6 import java.util.HashMap; 7 import java.util.Map; 8  9 import org.apache.commons.net.util.SubnetUtils;10 import org.apache.commons.net.util.SubnetUtils.SubnetInfo;11 12 public class FinderImpl implements Finder {13 14     private Map
     
       dataMap = new HashMap
      
       ();15     16     @Override17     public boolean loadFile(String fileName) {18         File file = new File(this.getClass().getClassLoader().getResource(fileName).getFile());19         try {20             FileReader fileReader = new FileReader(file);21             BufferedReader bufferedReader = new BufferedReader(fileReader);22             while(true) {23                 String nextLine = bufferedReader.readLine();24                 if(nextLine == null) {25                     break;26                 } else {27                     String str[] = nextLine.split(",");28                     dataMap.put(str[0], str[1]);29                 }30             }31         } catch (Exception e) {32             e.printStackTrace();33             return false;34         }35         return true;36     }37 38     @Override39     public int find(String ip) {40         for(String network : dataMap.keySet()) {41             boolean bingo = isInRange(ip, network);42             if(bingo) {43                 return Integer.parseInt(dataMap.get(network)); 44             }45         }46         return -1;47     }48     49     //核心代码，检索IP所属网段50     public boolean isInRange(String ip, String network) {51         String[] ips = ip.split("\\.");  52         int ipAddr = (Integer.parseInt(ips[0]) << 24)  53                 | (Integer.parseInt(ips[1]) << 16)  54                 | (Integer.parseInt(ips[2]) << 8) 55                 | Integer.parseInt(ips[3]);  56         int type = Integer.parseInt(network.replaceAll(".*/", ""));  57         int mask = 0xFFFFFFFF << (32 - type);  58         String networkIp = network.replaceAll("/.*", "");  59         String[] networkIps = networkIp.split("\\.");  60         int networkIpAddr = (Integer.parseInt(networkIps[0]) << 24)  61                 | (Integer.parseInt(networkIps[1]) << 16)  62                 | (Integer.parseInt(networkIps[2]) << 8)  63                 | Integer.parseInt(networkIps[3]);  64          return (ipAddr & mask) == (networkIpAddr & mask);65     }66     67     //也可以使用apache的net工具类68     public boolean isInRange2(String ip, String network) {69         SubnetInfo subnetInfo = new SubnetUtils(network).getInfo();70         return subnetInfo.isInRange(ip);71     }72     73     public static void main(String args[]) {74         FinderImpl finder = new FinderImpl();75         if(finder.loadFile("data.txt")) {76             int num = finder.find("1.1.1.1");77             System.out.println(num);78         }79     }80     81 }