String类型IP与int类型互转

之前无意中看到的一个阿里的面试题，然后就花了点时间去解决。原理就是利用int类型占用四个字节32位来存放ip地址的四段8位二进制数。

public class IpTest {    public static void main(String[] args) {        String ip = "192.168.23.106";        int intIp = stringIpToIntIp(ip);        System.out.println(intIp);        System.out.println(intIpToStringIp(intIp));    }    /**     * string类型ip转int类型ip     */    public static int stringIpToIntIp(String ip) {        String[] ips = ip.split("\\.");        if (ips.length != 4) {            throw new IllegalArgumentException("请传入正确的ipv4地址");        }        StringBuilder str = new StringBuilder();        for (String s : ips) {            int i = Integer.parseInt(s);            if (i > 255 || i < 0) {                throw new IllegalArgumentException("请传入正确的ipv4地址");            }            String bs = Integer.toBinaryString(i);            str.append(String.format("%8s", bs).replace(" ", "0"));        }        //二进制字符串转10进制,因为Integer.parseInt对负数转的问题,所以自己手写了转化的方法        int n = 0;        for (int i = 0; i < str.length(); i++) {            String a = str.substring(i, i + 1);            n = n << 1;            if (a.equals("1")) {                n = n | 1;            }        }        return n;    }    /**     * int类型ip转string类型ip     */    public static String intIpToStringIp(int intIp) {        String str = Integer.toBinaryString(intIp);        StringBuilder strIp = new StringBuilder();        for (int i = 0; i < 4; i++) {            int sIp = Integer.parseInt(str.substring(i * 8, (i + 1) * 8), 2);            strIp.append(sIp).append(".");        }        return strIp.substring(0, strIp.length() - 1);    }}