用JAVA實現了一個判斷某個IP是否在指定IP段內的方法，方便網站上使用黑白名單功能，有兩種方法，推薦使用方法一。

public class testIP {

	/**
	 * 判斷IP是否在指定IP段內，方法一（推薦）
	 * ipRange IP段（以'-'分隔）
	 * 
	 * @param ipRange
	 * @param ip
	 * @return boolean
	 */
	public static boolean ipIsInRange(String ip, String ipRange) {
		if (ipRange == null)
			throw new NullPointerException("IP段不能為空！");
		if (ip == null)
			throw new NullPointerException("IP不能為空！");
		ipRange = ipRange.trim();
		ip = ip.trim();
		final String REGX_IP = "((25[0-5]|2[0-4]\\d|1\\d{2}|[1-9]\\d|\\d)\\.){3}(25[0-5]|2[0-4]\\d|1\\d{2}|[1-9]\\d|\\d)";
		final String REGX_IPB = REGX_IP + "\\-" + REGX_IP;
		if (!ipRange.matches(REGX_IPB) || !ip.matches(REGX_IP))
			return false;
		int idx = ipRange.indexOf('-');
		String[] sips = ipRange.substring(0, idx).split("\\.");
		String[] sipe = ipRange.substring(idx + 1).split("\\.");
		String[] sipt = ip.split("\\.");
		long ips = 0L, ipe = 0L, ipt = 0L;
		for (int i = 0; i < 4; ++i) {
			ips = ips << 8 | Integer.parseInt(sips[i]);
			ipe = ipe << 8 | Integer.parseInt(sipe[i]);
			ipt = ipt << 8 | Integer.parseInt(sipt[i]);
		}
		if (ips > ipe) {
			long t = ips;
			ips = ipe;
			ipe = t;
		}
		return ips <= ipt && ipt <= ipe;
	}

	/*
	 * 判斷IP是否在指定IP段內，方法二
	 * ipRange IP段（以'-'分隔）
	 * 
	 * @param ipRange
	 * @param ip
	 * @return boolean
	 */
	public static boolean ipInRange(String ip, String ipRange) {
		int idx = ipRange.indexOf('-');
		String beginIP = ipRange.substring(0, idx);
		String endIP = ipRange.substring(idx + 1);
		return getIp2long(beginIP) <= getIp2long(ip)
				&& getIp2long(ip) <= getIp2long(endIP);
	}

	public static long getIp2long(String ip) {
		String[] ips = ip.split("\\.");
		long ip2long = 0L;
		for (int i = 0; i < 4; ++i) {
			ip2long = ip2long << 8 | Integer.parseInt(ips[i]);
		}
		return ip2long;

	}

	public static void main(String[] args) {
		// 判斷192.168.1.100 是否在IP段192.168.1.1-192.168.1.254內
		String ip = "192.168.18.100";
		String ipRange = "192.168.1.1-192.168.1.254";
		boolean isInRange = ipIsInRange(ip, ipRange);
		//boolean isInRange = ipInRange(ip, ipRange);
		System.out.println(isInRange);
	}