codeblocks，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

codeblocks，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 outputint b = 0;for (int i = 0; i < input.length(); i++) {char c = input.charAt(i);if (isBasic(c)) {output.append(c);b++;}}// Append delimiterif (b > 0) {output.append(DELIMITER);}int h = b;while (h < input.length()) {int m = Integer.MAX_VALUE;// Find the minimum code point >= nfor (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..35return c - '0' + 26;} else if (c - 'a' < 26) {// 'a'..'z' : 0..25return 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