IPv4正则表达式

package org.apache.http.conn.util;

public class InetAddressUtils {

    private InetAddressUtils() {
    }

    private static final String IPV4_BASIC_PATTERN_STRING =
            "(([1-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\\.){1}" + // initial first field, 1-255
            "(([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\\.){2}" + // following 2 fields, 0-255 followed by .
             "([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])"; // final field, 0-255

    private static final Pattern IPV4_PATTERN =
        Pattern.compile("^" + IPV4_BASIC_PATTERN_STRING + "$");
}