[Java][踩坑] 关于中文域名解析 Punycode 编码

[MrXiaoM]

我有一个朋友，他买了个域名，然后绑了 CNAME 和 SRV 记录到我的 Minecraft 服务器上，但可惜的是，Minecraft 客户端并无 Punycode 编码域名支持，然后我用网络爬虫 (低情商: 百度) 搜找到了 Punycode 转码的码子，以为就一劳永逸了，结果这玩意并不完全，下面的是我补好可以直接用的轮子。写得不是很好，如有错希望大佬能指出

public class Punycode {
	private static int TMIN = 1;
	private static int TMAX = 26;
	private static int BASE = 36;
	private static int INITIAL_N = 128;
	private static int INITIAL_BIAS = 72;
	private static int DAMP = 700;
	private static int SKEW = 38;
	private static char DELIMITER = '-';

	public static String encodeURL(String url) {
		if (!url.contains("."))
			return url;
		String mainContent = url.substring(0, url.lastIndexOf("."));
		String prefix = mainContent.contains(".") ? mainContent.substring(0, mainContent.lastIndexOf(".") + 1) : "";
		if (mainContent.contains("."))
			mainContent = mainContent.substring(mainContent.lastIndexOf(".") + 1);
		mainContent = Punycode.encode(mainContent, "xn--");
		String suffix = url.substring(url.lastIndexOf("."));
		return prefix + mainContent + suffix;
	}

	/**
	 * 
	 * Punycodes a unicode string. THIS IS NOT SUITABLE FOR UNICODE AND LETTER
	 * MIXING
	 *
	 * @param input Unicode string.
	 * 
	 * @return Punycoded string, but original text for throw an exception
	 * 
	 */
	public static String encode(String input) {
		return Punycode.encode(input, "");
	}

	/**
	 * 
	 * Punycodes a unicode string. THIS IS NOT SUITABLE FOR UNICODE AND LETTER
	 * MIXING
	 *
	 * @param input Unicode string.
	 * 
	 * @return Punycoded string, but original text for throw an exception
	 * 
	 */
	public static String encode(String input, String successPrefix) {
		int n = INITIAL_N;
		int delta = 0;
		int bias = INITIAL_BIAS;
		StringBuilder output = new StringBuilder();
		int b = 0;
		for (int i = 0; i < input.length(); i++) {
			char c = input.charAt(i);
			if (isBasic(c)) {
				output.append(c);
				b++;
			}
		}
		if(b >= input.length()) return output.toString();
		if (b > 0) {
			output.append(DELIMITER);
		}
		int h = b;
		while (h < input.length()) {
			int m = Integer.MAX_VALUE;
			for (int i = 0; i < input.length(); i++) {
				int c = input.charAt(i);
				if (c >= n && c < m) {
					m = c;
				}
			}
			if (m - n > (Integer.MAX_VALUE - delta) / (h + 1)) {
				return input;
			}
			delta = delta + (m - n) * (h + 1);
			n = m;
			for (int j = 0; j < input.length(); j++) {
				int c = input.charAt(j);
				if (c < n) {
					delta++;
					if (0 == delta) {
						return input;
					}
				}
				if (c == n) {
					int q = delta;
					for (int k = BASE;; k += BASE) {
						int t;

						if (k <= bias) {
							t = TMIN;
						} else if (k >= bias + TMAX) {
							t = TMAX;
						} else {
							t = k - bias;
						}
						if (q < t) {
							break;
						}
						output.append((char) digit2codepoint(t + (q - t) % (BASE - t)));
						q = (q - t) / (BASE - t);
					}
					output.append((char) digit2codepoint(q));
					bias = adapt(delta, h + 1, h == b);
					delta = 0;
					h++;
				}
			}
			delta++;
			n++;
		}
		output.insert(0, successPrefix);
		return output.toString();
	}

	private static int adapt(int delta, int numpoints, boolean first) {
		if (first) {
			delta = delta / DAMP;
		} else {
			delta = delta / 2;
		}
		delta = delta + (delta / numpoints);
		int k = 0;
		while (delta > ((BASE - TMIN) * TMAX) / 2) {
			delta = delta / (BASE - TMIN);
			k = k + BASE;
		}
		return k + ((BASE - TMIN + 1) * delta) / (delta + SKEW);
	}

	private static boolean isBasic(char c) {
		return c < 0x80;
	}

	private static int digit2codepoint(int d) {
		if (d < 26) {
			return d + 'a';
		} else if (d < 36) {
			return d - 26 + '0';
		} else {
			return d;
		}
	}
}

CSDN

那个朋友真不是我自己