Java正则表达式判断一个字符串是否是ipv4地址

public class StringTest {
    public static void main(String[] args) {
        String regex = "\A(25[0-5]|2[0-4]\d|[0-1]?\d?\d)(\.(25[0-5]|2[0-4]\d|[0-1]?\d?\d)){3}\z";
        String str1 = "1.1.1.0";
        boolean flag1 = str1.matches(regex);
        System.out.println(flag1);

        String str2 = "222";
        boolean flag2 = str2.matches(regex);
        System.out.println(flag2);
    }

}