偶尔会在数据中看到诸如' 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 或者等价的 

  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

  1. 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
  2. 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

       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

         private static final String[][] BASIC_ARRAY = {{"quot", "34"}, // " - double-quote
             {"amp", "38"}, // & - ampersand
             {"lt", "60"}, // < - less-than
             {"gt", "62"}, // > - greater-than
         };

         ISO8859_1_ARRAY

         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
             {"pide", "247"}, // pision 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

         static final String[][] HTML40_ARRAY = {
         // 
             {"fnof", "402"}, // latin small f with hook = function= florin, U+0192 ISOtech -->
             // 
             {"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 -->
             // 
             {"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 -->
             // 
             {"bull", "8226"}, // bullet = black small circle,U+2022 ISOpub -->
             // 
             {"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 -->
             // 
             {"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 -->
             // 
             // 
             {"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 -->
             // 
             {"uArr", "8657"}, // upwards double arrow, U+21D1 ISOamsa -->
             {"rArr", "8658"}, // rightwards double arrow,U+21D2 ISOtech -->
             // 
             {"dArr", "8659"}, // downwards double arrow, U+21D3 ISOamsa -->
             {"hArr", "8660"}, // left right double arrow,U+21D4 ISOamsa -->
             // 
             {"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 -->
             // 
             {"prod", "8719"}, // n-ary product = product sign,U+220F ISOamsb -->
             // 
             {"sum", "8721"}, // n-ary summation, U+2211 ISOamsb -->
             // 
             {"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 -->
             // 
             {"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 -->
             //  
             {"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 -->
             // 
             // 
             {"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 -->
             // 
             {"rang", "9002"}, // right-pointing angle bracket = ket,U+232A ISOtech -->
             // 
             // 
             {"loz", "9674"}, // lozenge, U+25CA ISOpub -->
             // 
             {"spades", "9824"}, // black spade suit, U+2660 ISOpub -->
             // 
             {"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 -->
         
             // 
             {"OElig", "338"}, // -- latin capital ligature OE,U+0152 ISOlat2 -->
             {"oelig", "339"}, // -- latin small ligature oe, U+0153 ISOlat2 -->
             // 
             {"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 -->
             // 
             {"circ", "710"}, // -- modifier letter circumflex accent,U+02C6 ISOpub -->
             {"tilde", "732"}, // small tilde, U+02DC ISOdia -->
             // 
             {"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 -->
             // 
             {"rsaquo", "8250"}, // single right-pointing angle quotation mark,U+203A ISO proposed -->
             // 
             {"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中,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