code:

public class TestSplitIP {
	public static void main(String[] args) {
		String request = "REJECT 172.16.12.100";
		String[] sip = request.split(" ");

		System.out.println(sip[0] + "-" + sip[1]);
		// result: REJECT-172.16.12.100

		IP ip = new IP(sip[1]);

		System.out.println(ip);
                // result: IP: 0.0.0.0
                // What shit is here?????
	}
}

class IP {
	int[] ip = new int[4];
	public IP(String str) {
		System.out.println(str);
		// result: 172.16.12.100

		String[] sip = str.split(".");
		System.out.println("sip.length = " + sip.length);
		// result: sip.length = 0
		// ???????????

		for (int i = 0; i < sip.length; ++i) {
			ip[i] = Integer.parseInt(sip[i]);
		}
	}

	public String toString() {
		String tmp = "";
		for (int i = 0; i < 4; ++i) {
			tmp = tmp + ip[i] + ((i == 3) ? "" : ".");
		}

		return "IP: " + tmp;
	}
}

code:
 String[] sip = str.split("\\."); 

code:

        String[] sip = str.split("[.]");