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);
        }
    }
    
}