谈谈html转义字符如何通过代码识别

偶尔会在数据中看到诸如& #39; 这样的字符，特征如下

以& #开头，中间是一串数字，以；结尾
以& 开头，中间一串字符，以；结尾

比如最常见的& nbsp; 或者等价的& #160;

浏览器遇到这些转义符，会转义回来，但如何通过代码识别？ org.apache.COMmons.lang.StringEscaPEUtils.unescapeHtML提供了很好的说明

遇到上面的第一种情况，中间是数字的，直接将数字（unicode）转为char
遇到第二情况，中间是字符，只能查映射表了,从映射表中找到字符对应的数字再转换为char 看看代码就一目了然了

看看HTML40如何定义的

复制代码代码如下:
static {
HTML40 = new EntITies();
fillWithHtml40Entities(HTML40);
}
static void fillWithHtml40Entities(Entities entities) {
entities.addEntities(BASIC_ARRAY);
entities.addEntities(ISO8859_1_ARRAY);
entities.addEntities(HTML40_ARRAY);
}

再看看BASIC_ARRAY、ISO8859_1_ARRAY、HTML40_ARRAY 分别是什么

BASIC_ARRAY

复制代码代码如下:
PRivate static final String[][] BASIC_ARRAY = { { "quot", "34"} , // " - double-quote
{ "amp", "38"} , // & - ampersand
{ "lt", "60"} , // - less-than
{ "gt", "62"} , // > - greater-than
} ;

ISO8859_1_ARRAY

复制代码代码如下:
static final String[][] ISO8859_1_ARRAY = { { "nbsp", "160"} , // non-breaking space
{ "iexcl", "161"} , // inverted exclamation mark
{ "cent", "162"} , // cent sign
{ "pound", "163"} , // pound sign
{ "curren", "164"} , // currency sign
{ "yen", "165"} , // yen sign = yuan sign
{ "brvbar", "166"} , // broken bar = broken vertical bar
{ "sect", "167"} , // section sign
{ "uml", "168"} , // diaeresis = spacing diaeresis
{ "copy", "169"} , // � - copyright sign
{ "orDF", "170"} , // feminine ordinal indicator
{ "laquo", "171"} , // left-pointing double angle quotation mark = left pointing guillemet
{ "not", "172"} , // not sign
{ "shy", "173"} , // soft hyphen = discretionary hyphen
{ "reg", "174"} , // � - registered trademark sign
{ "macr", "175"} , // macron = spacing macron = overline = APL overbar
{ "deg", "176"} , // degree sign
{ "plusmn", "177"} , // plus-minus sign = plus-or-minus sign
{ "sup2", "178"} , // superscript two = superscript digit two = squared
{ "suP3", "179"} , // superscript three = superscript digit three = cubed
{ "acute", "180"} , // acute accent = spacing acute
{ "micro", "181"} , // micro sign
{ "para", "182"} , // pilcrow sign = paragraph sign
{ "middot", "183"} , // middle dot = Georgian comma = Greek middle dot
{ "cedil", "184"} , // cedilla = spacing cedilla
{ "sup1", "185"} , // superscript one = superscript digit one
{ "ordm", "186"} , // masculine ordinal indicator
{ "raquo", "187"} , // right-pointing double angle quotation mark = right pointing guillemet
{ "frac14", "188"} , // vulgar fraction one quarter = fraction one quarter
{ "frac12", "189"} , // vulgar fraction one half = fraction one half
{ "frac34", "190"} , // vulgar fraction three quarters = fraction three quarters
{ "iquest", "191"} , // inverted question mark = turned question mark
{ "Agrave", "192"} , // � - uppercase A, grave accent
{ "Aacute", "193"} , // � - uppercase A, acute accent
{ "Acirc", "194"} , // � - uppercase A, circumflex accent
{ "Atilde", "195"} , // � - uppercase A, tilde
{ "Auml", "196"} , // � - uppercase A, umlaut
{ "Aring", "197"} , // � - uppercase A, ring
{ "AElig", "198"} , // � - uppercase AE
{ "Ccedil", "199"} , // � - uppercase C, cedilla
{ "Egrave", "200"} , // � - uppercase E, grave accent
{ "Eacute", "201"} , // � - uppercase E, acute accent
{ "Ecirc", "202"} , // � - uppercase E, circumflex accent
{ "Euml", "203"} , // � - uppercase E, umlaut
{ "Igrave", "204"} , // � - uppercase I, grave accent
{ "Iacute", "205"} , // � - uppercase I, acute accent
{ "Icirc", "206"} , // � - uppercase I, circumflex accent
{ "Iuml", "207"} , // � - uppercase I, umlaut
{ "ETH", "208"} , // � - uppercase Eth, Icelandic
{ "Ntilde", "209"} , // � - uppercase N, tilde
{ "Ograve", "210"} , // � - uppercase O, grave accent
{ "Oacute", "211"} , // � - uppercase O, acute accent
{ "Ocirc", "212"} , // � - uppercase O, circumflex accent
{ "Otilde", "213"} , // � - uppercase O, tilde
{ "Ouml", "214"} , // � - uppercase O, umlaut
{ "times", "215"} , // multiplication sign
{ "Oslash", "216"} , // � - uppercase O, slash
{ "Ugrave", "217"} , // � - uppercase U, grave accent
{ "Uacute", "218"} , // � - uppercase U, acute accent
{ "Ucirc", "219"} , // � - uppercase U, circumflex accent
{ "Uuml", "220"} , // � - uppercase U, umlaut
{ "Yacute", "221"} , // � - uppercase Y, acute accent
{ "THORN", "222"} , // � - uppercase THORN, Icelandic
{ "szlig", "223"} , // � - lowercase sharps, German
{ "agrave", "224"} , // � - lowercase a, grave accent
{ "aacute", "225"} , // � - lowercase a, acute accent
{ "acirc", "226"} , // � - lowercase a, circumflex accent
{ "atilde", "227"} , // � - lowercase a, tilde
{ "auml", "228"} , // � - lowercase a, umlaut
{ "aring", "229"} , // � - lowercase a, ring
{ "aelig", "230"} , // � - lowercase ae
{ "ccedil", "231"} , // � - lowercase c, cedilla
{ "egrave", "232"} , // � - lowercase e, grave accent
{ "eacute", "233"} , // � - lowercase e, acute accent
{ "ecirc", "234"} , // � - lowercase e, circumflex accent
{ "euml", "235"} , // � - lowercase e, umlaut
{ "igrave", "236"} , // � - lowercase i, grave accent
{ "iacute", "237"} , // � - lowercase i, acute accent
{ "icirc", "238"} , // � - lowercase i, circumflex accent
{ "iuml", "239"} , // � - lowercase i, umlaut
{ "eth", "240"} , // � - lowercase eth, Icelandic
{ "ntilde", "241"} , // � - lowercase n, tilde
{ "ograve", "242"} , // � - lowercase o, grave accent
{ "oacute", "243"} , // � - lowercase o, acute accent
{ "ocirc", "244"} , // � - lowercase o, circumflex accent
{ "otilde", "245"} , // � - lowercase o, tilde
{ "ouml", "246"} , // � - lowercase o, umlaut
{ "divide", "247"} , // division sign
{ "oslash", "248"} , // � - lowercase o, slash
{ "ugrave", "249"} , // � - lowercase u, grave accent
{ "uacute", "250"} , // � - lowercase u, acute accent
{ "ucirc", "251"} , // � - lowercase u, circumflex accent
{ "uuml", "252"} , // � - lowercase u, umlaut
{ "yacute", "253"} , // � - lowercase y, acute accent
{ "thorn", "254"} , // � - lowercase thorn, Icelandic
{ "yuml", "255"} , // � - lowercase y, umlaut
} ;

HTML40_ARRAY

复制代码代码如下:
static final String[][] HTML40_ARRAY = {
// !-- Latin Extended-B -->
{ "fnof", "402"} , // latin small f with hook = function= florin, U+0192 ISOtech -->
// !-- Greek -->
{ "Alpha", "913"} , // greek capital letter alpha, U+0391 -->
{ "Beta", "914"} , // greek capital letter beta, U+0392 -->
{ "Gamma", "915"} , // greek capital letter gamma,U+0393 ISOgrk3 -->
{ "Delta", "916"} , // greek capital letter delta,U+0394 ISOgrk3 -->
{ "Epsilon", "917"} , // greek capital letter epsilon, U+0395 -->
{ "Zeta", "918"} , // greek capital letter zeta, U+0396 -->
{ "Eta", "919"} , // greek capital letter eta, U+0397 -->
{ "Theta", "920"} , // greek capital letter theta,U+0398 ISOgrk3 -->
{ "Iota", "921"} , // greek capital letter iota, U+0399 -->
{ "Kappa", "922"} , // greek capital letter kappa, U+039A -->
{ "Lambda", "923"} , // greek capital letter lambda,U+039B ISOgrk3 -->
{ "Mu", "924"} , // greek capital letter mu, U+039C -->
{ "Nu", "925"} , // greek capital letter nu, U+039D -->
{ "Xi", "926"} , // greek capital letter xi, U+039E ISOgrk3 -->
{ "Omicron", "927"} , // greek capital letter omicron, U+039F -->
{ "Pi", "928"} , // greek capital letter pi, U+03A0 ISOgrk3 -->
{ "Rho", "929"} , // greek capital letter rho, U+03A1 -->
// !-- there is no Sigmaf, and no U+03A2 character either -->
{ "Sigma", "931"} , // greek capital letter sigma,U+03A3 ISOgrk3 -->
{ "Tau", "932"} , // greek capital letter tau, U+03A4 -->
{ "Upsilon", "933"} , // greek capital letter upsilon,U+03A5 ISOgrk3 -->
{ "Phi", "934"} , // greek capital letter phi,U+03A6 ISOgrk3 -->
{ "Chi", "935"} , // greek capital letter chi, U+03A7 -->
{ "Psi", "936"} , // greek capital letter psi,U+03A8 ISOgrk3 -->
{ "Omega", "937"} , // greek capital letter omega,U+03A9 ISOgrk3 -->
{ "alpha", "945"} , // greek small letter alpha,U+03B1 ISOgrk3 -->
{ "beta", "946"} , // greek small letter beta, U+03B2 ISOgrk3 -->
{ "gamma", "947"} , // greek small letter gamma,U+03B3 ISOgrk3 -->
{ "delta", "948"} , // greek small letter delta,U+03B4 ISOgrk3 -->
{ "epsilon", "949"} , // greek small letter epsilon,U+03B5 ISOgrk3 -->
{ "zeta", "950"} , // greek small letter zeta, U+03B6 ISOgrk3 -->
{ "eta", "951"} , // greek small letter eta, U+03B7 ISOgrk3 -->
{ "theta", "952"} , // greek small letter theta,U+03B8 ISOgrk3 -->
{ "iota", "953"} , // greek small letter iota, U+03B9 ISOgrk3 -->
{ "kappa", "954"} , // greek small letter kappa,U+03BA ISOgrk3 -->
{ "lambda", "955"} , // greek small letter lambda,U+03BB ISOgrk3 -->
{ "mu", "956"} , // greek small letter mu, U+03BC ISOgrk3 -->
{ "nu", "957"} , // greek small letter nu, U+03BD ISOgrk3 -->
{ "xi", "958"} , // greek small letter xi, U+03BE ISOgrk3 -->
{ "omicron", "959"} , // greek small letter omicron, U+03BF NEW -->
{ "pi", "960"} , // greek small letter pi, U+03C0 ISOgrk3 -->
{ "rho", "961"} , // greek small letter rho, U+03C1 ISOgrk3 -->
{ "sigmaf", "962"} , // greek small letter final sigma,U+03C2 ISOgrk3 -->
{ "sigma", "963"} , // greek small letter sigma,U+03C3 ISOgrk3 -->
{ "tau", "964"} , // greek small letter tau, U+03C4 ISOgrk3 -->
{ "upsilon", "965"} , // greek small letter upsilon,U+03C5 ISOgrk3 -->
{ "phi", "966"} , // greek small letter phi, U+03C6 ISOgrk3 -->
{ "chi", "967"} , // greek small letter chi, U+03C7 ISOgrk3 -->
{ "psi", "968"} , // greek small letter psi, U+03C8 ISOgrk3 -->
{ "omega", "969"} , // greek small letter omega,U+03C9 ISOgrk3 -->
{ "thetasym", "977"} , // greek small letter theta symbol,U+03D1 NEW -->
{ "upsih", "978"} , // greek upsilon with hook symbol,U+03D2 NEW -->
{ "piv", "982"} , // greek pi symbol, U+03D6 ISOgrk3 -->
// !-- General Punctuation -->
{ "bull", "8226"} , // bullet = black small circle,U+2022 ISOpub -->
// !-- bullet is NOT the same as bullet operator, U+2219 -->
{ "hellip", "8230"} , // horizontal ellipsis = three dot leader,U+2026 ISOpub -->
{ "prime", "8242"} , // prime = minutes = feet, U+2032 ISOtech -->
{ "Prime", "8243"} , // double prime = seconds = inches,U+2033 ISOtech -->
{ "oline", "8254"} , // overline = spacing overscore,U+203E NEW -->
{ "frasl", "8260"} , // fraction slash, U+2044 NEW -->
// !-- Letterlike Symbols -->
{ "weierp", "8472"} , // script capital P = power set= Weierstrass p, U+2118 ISOAmso -->
{ "image", "8465"} , // blackletter capital I = imaginary part,U+2111 ISOamso -->
{ "real", "8476"} , // blackletter capital R = real part symbol,U+211C ISOamso -->
{ "trade", "8482"} , // trade mark sign, U+2122 ISOnum -->
{ "alefsym", "8501"} , // alef symbol = First transfinite cardinal,U+2135 NEW -->
// !-- alef symbol is NOT the same as hebrew letter alef,U+05D0 although the
// same glyph could be used to depict both characters -->
// !-- Arrows -->
{ "larr", "8592"} , // leftwards arrow, U+2190 ISOnum -->
{ "uarr", "8593"} , // upwards arrow, U+2191 ISOnum-->
{ "rarr", "8594"} , // rightwards arrow, U+2192 ISOnum -->
{ "darr", "8595"} , // downwards arrow, U+2193 ISOnum -->
{ "harr", "8596"} , // left right arrow, U+2194 ISOamsa -->
{ "crarr", "8629"} , // downwards arrow with corner leftwards= carriage return, U+21B5 NEW -->
{ "lArr", "8656"} , // leftwards double arrow, U+21D0 ISOtech -->
// !-- ISO 10646 does not say that lArr is the same as the 'is implied by'
// arrow but also does not have any other character for that function.
// So ? lArr canbe used for 'is implied by' as ISOtech suggests -->
{ "uArr", "8657"} , // upwards double arrow, U+21D1 ISOamsa -->
{ "rArr", "8658"} , // rightwards double arrow,U+21D2 ISOtech -->
// !-- ISO 10646 does not say this is the 'implies' character but does not
// have another character with this function so ?rArr can be used for
// 'implies' as ISOtech suggests -->
{ "dArr", "8659"} , // downwards double arrow, U+21D3 ISOamsa -->
{ "hArr", "8660"} , // left right double arrow,U+21D4 ISOamsa -->
// !-- Mathematical Operators -->
{ "forall", "8704"} , // for all, U+2200 ISOtech -->
{ "part", "8706"} , // partial differential, U+2202 ISOtech -->
{ "exist", "8707"} , // there exists, U+2203 ISOtech -->
{ "empty", "8709"} , // empty set = null set = diameter,U+2205 ISOamso -->
{ "nabla", "8711"} , // nabla = backward difference,U+2207 ISOtech -->
{ "isin", "8712"} , // element of, U+2208 ISOtech -->
{ "notin", "8713"} , // not an element of, U+2209 ISOtech -->
{ "ni", "8715"} , // contains as member, U+220B ISOtech -->
// !-- should there be a more memorable name than 'ni'? -->
{ "prod", "8719"} , // n-ary product = product sign,U+220F ISOamsb -->
// !-- prod is NOT the same character as U+03A0 'greek capital letter pi'
// though the same glyph might be used for both -->
{ "sum", "8721"} , // n-ary summation, U+2211 ISOamsb -->
// !-- sum is NOT the same character as U+03A3 'greek capital letter sigma'
// though the same glyph might be used for both -->
{ "minus", "8722"} , // minus sign, U+2212 ISOtech -->
{ "lowast", "8727"} , // asterisk operator, U+2217 ISOtech -->
{ "radic", "8730"} , // square root = radical sign,U+221A ISOtech -->
{ "prop", "8733"} , // proportional to, U+221D ISOtech -->
{ "infin", "8734"} , // infinity, U+221E ISOtech -->
{ "ang", "8736"} , // angle, U+2220 ISOamso -->
{ "and", "8743"} , // LOGical and = wEdge, U+2227 ISOtech -->
{ "or", "8744"} , // logical or = vee, U+2228 ISOtech -->
{ "cap", "8745"} , // intersection = cap, U+2229 ISOtech -->
{ "cup", "8746"} , // union = cup, U+222A ISOtech -->
{ "int", "8747"} , // integral, U+222B ISOtech -->
{ "there4", "8756"} , // therefore, U+2234 ISOtech -->
{ "sim", "8764"} , // tilde operator = VARies with = similar to,U+223C ISOtech -->
// !-- tilde operator is NOT the same character as the tilde, U+007E,although
// the same glyph might be used to represent both -->
{ "cong", "8773"} , // approxiMATEly equal to, U+2245 ISOtech -->
{ "asymp", "8776"} , // almost equal to = asymptotic to,U+2248 ISOamsr -->
{ "ne", "8800"} , // not equal to, U+2260 ISOtech -->
{ "equiv", "8801"} , // identical to, U+2261 ISOtech -->
{ "le", "8804"} , // less-than or equal to, U+2264 ISOtech -->
{ "ge", "8805"} , // greater-than or equal to,U+2265 ISOtech -->
{ "sub", "8834"} , // subset of, U+2282 ISOtech -->
{ "sup", "8835"} , // superset of, U+2283 ISOtech -->
// !-- note that nsup, 'not a superset of, U+2283' is not covered by the
// Symbol font encoding and is not included. Should it be, for symmetry?
// It is in ISOamsn --> !ENTITY nsub", "8836"} ,
// not a subset of, U+2284 ISOamsn -->
{ "sube", "8838"} , // subset of or equal to, U+2286 ISOtech -->
{ "supe", "8839"} , // superset of or equal to,U+2287 ISOtech -->
{ "oplus", "8853"} , // circled plus = direct sum,U+2295 ISOamsb -->
{ "otimes", "8855"} , // circled times = vector product,U+2297 ISOamsb -->
{ "perp", "8869"} , // up tack = orthogonal to = perpendicular,U+22A5 ISOtech -->
{ "sdot", "8901"} , // dot operator, U+22C5 ISOamsb -->
// !-- dot operator is NOT the same character as U+00B7 middle dot -->
// !-- Miscellaneous Technical -->
{ "lceil", "8968"} , // left ceiling = apl upstile,U+2308 ISOamsc -->
{ "rceil", "8969"} , // right ceiling, U+2309 ISOamsc -->
{ "lfloor", "8970"} , // left floor = apl downstile,U+230A ISOamsc -->
{ "rfloor", "8971"} , // right floor, U+230B ISOamsc -->
{ "lang", "9001"} , // left-pointing angle bracket = bra,U+2329 ISOtech -->
// !-- lang is NOT the same character as U+003C 'less than' or U+2039 'single left-pointing angle quotation
// mark' -->
{ "rang", "9002"} , // right-pointing angle bracket = ket,U+232A ISOtech -->
// !-- rang is NOT the same character as U+003E 'greater than' or U+203A
// 'single right-pointing angle quotation mark' -->
// !-- Geometric Shapes -->
{ "loz", "9674"} , // lozenge, U+25CA ISOpub -->
// !-- Miscellaneous Symbols -->
{ "spades", "9824"} , // black spade suit, U+2660 ISOpub -->
// !-- black here seems to mean filled as opposed to hollow -->
{ "clubs", "9827"} , // black club suit = shamrock,U+2663 ISOpub -->
{ "hearts", "9829"} , // black heart suit = valentine,U+2665 ISOpub -->
{ "diams", "9830"} , // black diamond suit, U+2666 ISOpub -->
// !-- Latin Extended-A -->
{ "OElig", "338"} , // -- latin capital ligature OE,U+0152 ISOlat2 -->
{ "oelig", "339"} , // -- latin small ligature oe, U+0153 ISOlat2 -->
// !-- ligature is a misnomer, this is a separate character in some languages -->
{ "Scaron", "352"} , // -- latin capital letter S with caron,U+0160 ISOlat2 -->
{ "scaron", "353"} , // -- latin small letter s with caron,U+0161 ISOlat2 -->
{ "Yuml", "376"} , // -- latin capital letter Y with diaeresis,U+0178 ISOlat2 -->
// !-- Spacing Modifier Letters -->
{ "circ", "710"} , // -- modifier letter circumflex accent,U+02C6 ISOpub -->
{ "tilde", "732"} , // small tilde, U+02DC ISOdia -->
// !-- General Punctuation -->
{ "ensp", "8194"} , // en space, U+2002 ISOpub -->
{ "emsp", "8195"} , // em space, U+2003 ISOpub -->
{ "thinsp", "8201"} , // thin space, U+2009 ISOpub -->
{ "zwnj", "8204"} , // zero width non-joiner,U+200C NEW Rfc 2070 -->
{ "zwj", "8205"} , // zero width joiner, U+200D NEW RFC 2070 -->
{ "lrm", "8206"} , // left-to-right mark, U+200E NEW RFC 2070 -->
{ "rlm", "8207"} , // right-to-left mark, U+200F NEW RFC 2070 -->
{ "ndash", "8211"} , // en dash, U+2013 ISOpub -->
{ "mdash", "8212"} , // em dash, U+2014 ISOpub -->
{ "lsquo", "8216"} , // left single quotation mark,U+2018 ISOnum -->
{ "rsquo", "8217"} , // right single quotation mark,U+2019 ISOnum -->
{ "sbquo", "8218"} , // single low-9 quotation mark, U+201A NEW -->
{ "ldquo", "8220"} , // left double quotation mark,U+201C ISOnum -->
{ "rdquo", "8221"} , // right double quotation mark,U+201D ISOnum -->
{ "bdquo", "8222"} , // double low-9 quotation mark, U+201E NEW -->
{ "dagger", "8224"} , // dagger, U+2020 ISOpub -->
{ "Dagger", "8225"} , // double dagger, U+2021 ISOpub -->
{ "permil", "8240"} , // per mille sign, U+2030 ISOtech -->
{ "lsaquo", "8249"} , // single left-pointing angle quotation mark,U+2039 ISO proposed -->
// !-- lsaquo is proposed but not yet ISO standardized -->
{ "rsaquo", "8250"} , // single right-pointing angle quotation mark,U+203A ISO proposed -->
// !-- rsaquo is proposed but not yet ISO standardized -->
{ "euro", "8364"} , // -- euro sign, U+20AC NEW -->
} ;

再扩展下

从前面可以看到转义字符中间的那段数字是unicode，那么 这个 转移字符可以 随便构造了 ，并不限于上面的定义，比如 中的unicode是20013，那么构造一个转移字符& #20013; ,经过浏览器的渲染 就变回中了 ,虽然不必这么绕为了显示一个字符，但如果在一些不方便传输特殊字符的场景 就可以派上用途了

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