Punycode与中文互转

Punycode是一个根据RFC 3492标准而制定的编码系统，主要用于把域名从地方语言所采用的Unicode编码转换成为可用于DNS系统的编码

“中文域名”不被标准的解析服务器支持，需转化为Punycode码进行解析，例如“百度.中国”的转码为： xn--wxTr44c.xn--fiqs8S

目前，因为操作系统的核心都是英文组成，DNS服务器的解析也是由英文代码交换，所以DNS服务器上并不支持直接的中文域名解析，所有中文域名的解析都需要转成Punycode码，然后由DNS解析Punycode码

其实目前所说的各种浏览器完美支持中文域名，只是浏览器中主动加入了中文域名自动转码，不需要再次安装中文域名转码控件来完成整个流程

如在浏览器中输入"北京大学.com”，然后通过wireshark抓包

GET http://xn--1lq90ic7fzpc.com/ HTTP/1.1

 

将原作者的.Net版本修改为了Java版本，这里感谢下原作者

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

	/**
	 * Punycodes a unicode string.
	 * 
	 * @param input
	 *            Unicode string.
	 * 
	 * @return Punycoded string.
	 */
	public static String encode(String input) throws Exception {
		int n = INITIAL_N;
		int delta = 0;
		int bias = INITIAL_BIAS;
		StringBuilder output = new StringBuilder();
		// Copy all basic code points to the output
		int b = 0;
		for (int i = 0; i < input.length(); i++) {
			char c = input.charAt(i);
			if (isBasic(c)) {
				output.append(c);
				b++;
			}
		}
		// Append delimiter
		if (b > 0) {
			output.append(DELIMITER);
		}
		int h = b;
		while (h < input.length()) {
			int m = Integer.MAX_VALUE;
			// Find the minimum code point >= n
			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)) {
				throw new Exception("OVERFLOW");
			}
			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) {
						throw new Exception("OVERFLOW");
					}
				}
				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++;
		}
		return output.toString();
	}

	/**
	 * Decode a punycoded string.
	 * 
	 * @param input
	 *            Punycode string
	 * 
	 * @return Unicode string.
	 */
	public static String decode(String input) throws Exception {
		int n = INITIAL_N;
		int i = 0;
		int bias = INITIAL_BIAS;
		StringBuilder output = new StringBuilder();
		int d = input.lastIndexOf(DELIMITER);
		if (d > 0) {
			for (int j = 0; j < d; j++) {
				char c = input.charAt(j);
				if (!isBasic(c)) {
					throw new Exception("BAD_INPUT");
				}
				output.append(c);
			}
			d++;
		} else {
			d = 0;
		}
		while (d < input.length()) {
			int oldi = i;
			int w = 1;
			for (int k = BASE;; k += BASE) {
				if (d == input.length()) {
					throw new Exception("BAD_INPUT");
				}
				int c = input.charAt(d++);
				int digit = codepoint2digit(c);
				if (digit > (Integer.MAX_VALUE - i) / w) {
					throw new Exception("OVERFLOW");
				}
				i = i + digit * w;
				int t;
				if (k <= bias) {
					t = TMIN;
				} else if (k >= bias + TMAX) {
					t = TMAX;
				} else {
					t = k - bias;
				}
				if (digit < t) {
					break;
				}
				w = w * (BASE - t);
			}
			bias = adapt(i - oldi, output.length() + 1, oldi == 0);
			if (i / (output.length() + 1) > Integer.MAX_VALUE - n) {
				throw new Exception("OVERFLOW");
			}
			n = n + i / (output.length() + 1);
			i = i % (output.length() + 1);
			output.insert(i, (char) n);
			i++;
		}
		return output.toString();
	}

	public 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);
	}

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

	public static int digit2codepoint(int d) throws Exception {
		if (d < 26) {
			// 0..25 : 'a'..'z'
			return d + 'a';
		} else if (d < 36) {
			// 26..35 : '0'..'9';
			return d - 26 + '0';
		} else {
			throw new Exception("BAD_INPUT");
		}
	}

	public static int codepoint2digit(int c) throws Exception {
		if (c - '0' < 10) {
			// '0'..'9' : 26..35
			return c - '0' + 26;
		} else if (c - 'a' < 26) {
			// 'a'..'z' : 0..25
			return c - 'a';
		} else {
			throw new Exception("BAD_INPUT");
		}
	}

	public static void main(String[] args) throws Exception {
		 String strPunycode ="xn--"+ CharsetTool.encode("北京大学");
		 System.out.println(strPunycode);
		 String strChinese = CharsetTool.decode("1lq90ic7fzpc"); 
		 System.out.println(strChinese);
	}
}

运行结果为：

xn--1lq90ic7fzpc
北京大学

可以使用在线Punycode转码工具验证转码的正确性

遗憾的是并不支持“百度.中国”这种带有特殊字符“.”以及“中123国”这种混杂有数字的字符串转码

转载于:https://www.cnblogs.com/sean-zou/p/3710006.html