IP段转CIDR

经常使用nginx、apache时候需要对某个ip段进行白名单或黑名单控制，而它的配置是以CIDR的方式进行的，所以此工具可以方便的做到从IP段到CIDR的转换。

import java.util.ArrayList;
import java.util.List;
 
public class Ip2Cidr {
 
 
    public static void main(String[] args) {
        System.out.println(range2cidrlist("10.104.0.12","10.104.0.35"));
    }
 
    public static List<String> range2cidrlist(String startIp, String endIp) {
        long start = ipToLong(startIp);
        long end = ipToLong(endIp);
 
        ArrayList<String> pairs = new ArrayList<String>();
        while (end >= start) {
            byte maxsize = 32;
            while (maxsize > 0) {
                long mask = CIDR2MASK[maxsize - 1];
                long maskedBase = start & mask;
 
                if (maskedBase != start) {
                    break;
                }
 
                maxsize--;
            }
            double x = Math.log(end - start + 1) / Math.log(2);
            byte maxdiff = (byte) (32 - Math.floor(x));
            if (maxsize < maxdiff) {
                maxsize = maxdiff;
            }
            String ip = longToIP(start);
            pairs.add(ip + "/" + maxsize);
            start += Math.pow(2, (32 - maxsize));
        }
        return pairs;
    }
 
    public static final int[] CIDR2MASK = new int[] { 0x00000000, 0x80000000,
                                                      0xC0000000, 0xE0000000, 0xF0000000, 0xF8000000, 0xFC000000,
                                                      0xFE000000, 0xFF000000, 0xFF800000, 0xFFC00000, 0xFFE00000,
                                                      0xFFF00000, 0xFFF80000, 0xFFFC0000, 0xFFFE0000, 0xFFFF0000,
                                                      0xFFFF8000, 0xFFFFC000, 0xFFFFE000, 0xFFFFF000, 0xFFFFF800,
                                                      0xFFFFFC00, 0xFFFFFE00, 0xFFFFFF00, 0xFFFFFF80, 0xFFFFFFC0,
                                                      0xFFFFFFE0, 0xFFFFFFF0, 0xFFFFFFF8, 0xFFFFFFFC, 0xFFFFFFFE,
                                                      0xFFFFFFFF };
 
    private static long ipToLong(String strIP) {
        long[] ip = new long[4];
        String[] ipSec = strIP.split("\\.");
        for (int k = 0; k < 4; k++) {
            ip[k] = Long.valueOf(ipSec[k]);
        }
 
        return (ip[0] << 24) + (ip[1] << 16) + (ip[2] << 8) + ip[3];
    }
 
    private static String longToIP(long longIP) {
        StringBuffer sb = new StringBuffer("");
        sb.append(String.valueOf(longIP >>> 24));
        sb.append(".");
        sb.append(String.valueOf((longIP & 0x00FFFFFF) >>> 16));
        sb.append(".");
        sb.append(String.valueOf((longIP & 0x0000FFFF) >>> 8));
        sb.append(".");
        sb.append(String.valueOf(longIP & 0x000000FF));
 
        return sb.toString();
    }
}