HtmlEncoder.java

import java.util.Collections;
import java.util.HashMap;
import java.util.Map;

public class HtmlEncoder {

  private static final char REPLACEMENT_CHAR = '\ufffd';
  private static final String REPLACEMENT_HEX = "fffd";
  private static Map<Character,String> characterToEntityMap; // statically initialized
  /**
   * Initialize an array to mark which characters are to be encoded. Store the hex
   * string for that character to save time later. If the character shouldn't be
   * encoded, then store null.
   */
  private static final String[] encodedCharsCache = new String[256];

  public static String encodeForHTML(String input) {
    return encode(input);
  }

  // note: bases encodeForHTML() from ESAPI. Unfortunately ESAPI requires configuration in properties which
  // is a pain if you just need to encode
  private static String encode(String input) {
    StringBuilder sb = new StringBuilder();
    for (int i = 0; i < input.length(); i++) {
      char c = input.charAt(i);
      sb.append(encodeCharacter(c));
    }
    return sb.toString();
  }

  private static String toHex(char c) {
    return Integer.toHexString(c);
  }

  private static String getHexForNonAlphanumeric(char c)  {
      // note: we cache only up to 256 characters (ASCII)
    return c < 0xFF ? encodedCharsCache[c] : toHex(c);
  }

  private static String encodeCharacter( Character c ) {

    // check for immune characters
    if ( c == ',' || c == '.' || c == '-' || c == '_' || c == ' ') {
      return ""+c;
    }

    // check for alphanumeric characters
    String hex = getHexForNonAlphanumeric(c);
    if ( hex == null ) { // means we should not encode the character
      return ""+c;
    }

    // check for illegal characters
    if ( ( c <= 0x1f && c != '\t' && c != '\n' && c != '\r' ) || ( c >= 0x7f && c <= 0x9f ) )
    {
      hex = REPLACEMENT_HEX; // Let's entity encode this instead of returning it
      c = REPLACEMENT_CHAR;
    }

    // check if there's a defined entity
    String entityName = (String) characterToEntityMap.get(c);
    if (entityName != null) {
      return "&" + entityName + ";";
    }

    // return hex representation of entity
    return "&#x" + hex + ";";
  }

  static {
    for ( char c = 0; c < 0xFF; c++ ) {
      if ( c >= 0x30 && c <= 0x39 || c >= 0x41 && c <= 0x5A || c >= 0x61 && c <= 0x7A ) {
        encodedCharsCache[c] = null;
      } else {
        encodedCharsCache[c] = toHex(c).intern();
      }
    }

    Map<Character, String> map = new HashMap<Character,String>(252);

    map.put((char)34,  "quot"); /* quotation mark */
    map.put((char)38,  "amp");   /* ampersand */
    map.put((char)60,  "lt");  /* less-than sign */
    map.put((char)62,  "gt");  /* greater-than sign */
    map.put((char)160, "nbsp"); /* no-break space */
    map.put((char)161, "iexcl");  /* inverted exclamation mark */
    map.put((char)162, "cent"); /* cent sign */
    map.put((char)163, "pound");  /* pound sign */
    map.put((char)164, "curren"); /* currency sign */
    map.put((char)165, "yen");   /* yen sign */
    map.put((char)166, "brvbar"); /* broken bar */
    map.put((char)167, "sect"); /* section sign */
    map.put((char)168, "uml");   /* diaeresis */
    map.put((char)169, "copy"); /* copyright sign */
    map.put((char)170, "ordf"); /* feminine ordinal indicator */
    map.put((char)171, "laquo");  /* left-pointing double angle quotation mark */
    map.put((char)172, "not");   /* not sign */
    map.put((char)173, "shy");   /* soft hyphen */
    map.put((char)174, "reg");   /* registered sign */
    map.put((char)175, "macr"); /* macron */
    map.put((char)176, "deg");   /* degree sign */
    map.put((char)177, "plusmn"); /* plus-minus sign */
    map.put((char)178, "sup2"); /* superscript two */
    map.put((char)179, "sup3"); /* superscript three */
    map.put((char)180, "acute");  /* acute accent */
    map.put((char)181, "micro");  /* micro sign */
    map.put((char)182, "para"); /* pilcrow sign */
    map.put((char)183, "middot"); /* middle dot */
    map.put((char)184, "cedil");  /* cedilla */
    map.put((char)185, "sup1"); /* superscript one */
    map.put((char)186, "ordm"); /* masculine ordinal indicator */
    map.put((char)187, "raquo");  /* right-pointing double angle quotation mark */
    map.put((char)188, "frac14"); /* vulgar fraction one quarter */
    map.put((char)189, "frac12"); /* vulgar fraction one half */
    map.put((char)190, "frac34"); /* vulgar fraction three quarters */
    map.put((char)191, "iquest"); /* inverted question mark */
    map.put((char)192, "Agrave"); /* Latin capital letter a with grave */
    map.put((char)193, "Aacute"); /* Latin capital letter a with acute */
    map.put((char)194, "Acirc");  /* Latin capital letter a with circumflex */
    map.put((char)195, "Atilde"); /* Latin capital letter a with tilde */
    map.put((char)196, "Auml"); /* Latin capital letter a with diaeresis */
    map.put((char)197, "Aring");  /* Latin capital letter a with ring above */
    map.put((char)198, "AElig");  /* Latin capital letter ae */
    map.put((char)199, "Ccedil"); /* Latin capital letter c with cedilla */
    map.put((char)200, "Egrave"); /* Latin capital letter e with grave */
    map.put((char)201, "Eacute"); /* Latin capital letter e with acute */
    map.put((char)202, "Ecirc");  /* Latin capital letter e with circumflex */
    map.put((char)203, "Euml"); /* Latin capital letter e with diaeresis */
    map.put((char)204, "Igrave"); /* Latin capital letter i with grave */
    map.put((char)205, "Iacute"); /* Latin capital letter i with acute */
    map.put((char)206, "Icirc");  /* Latin capital letter i with circumflex */
    map.put((char)207, "Iuml"); /* Latin capital letter i with diaeresis */
    map.put((char)208, "ETH");   /* Latin capital letter eth */
    map.put((char)209, "Ntilde"); /* Latin capital letter n with tilde */
    map.put((char)210, "Ograve"); /* Latin capital letter o with grave */
    map.put((char)211, "Oacute"); /* Latin capital letter o with acute */
    map.put((char)212, "Ocirc");  /* Latin capital letter o with circumflex */
    map.put((char)213, "Otilde"); /* Latin capital letter o with tilde */
    map.put((char)214, "Ouml"); /* Latin capital letter o with diaeresis */
    map.put((char)215, "times");  /* multiplication sign */
    map.put((char)216, "Oslash"); /* Latin capital letter o with stroke */
    map.put((char)217, "Ugrave"); /* Latin capital letter u with grave */
    map.put((char)218, "Uacute"); /* Latin capital letter u with acute */
    map.put((char)219, "Ucirc");  /* Latin capital letter u with circumflex */
    map.put((char)220, "Uuml"); /* Latin capital letter u with diaeresis */
    map.put((char)221, "Yacute"); /* Latin capital letter y with acute */
    map.put((char)222, "THORN");  /* Latin capital letter thorn */
    map.put((char)223, "szlig");  /* Latin small letter sharp sXCOMMAX German Eszett */
    map.put((char)224, "agrave"); /* Latin small letter a with grave */
    map.put((char)225, "aacute"); /* Latin small letter a with acute */
    map.put((char)226, "acirc");  /* Latin small letter a with circumflex */
    map.put((char)227, "atilde"); /* Latin small letter a with tilde */
    map.put((char)228, "auml"); /* Latin small letter a with diaeresis */
    map.put((char)229, "aring");  /* Latin small letter a with ring above */
    map.put((char)230, "aelig");  /* Latin lowercase ligature ae */
    map.put((char)231, "ccedil"); /* Latin small letter c with cedilla */
    map.put((char)232, "egrave"); /* Latin small letter e with grave */
    map.put((char)233, "eacute"); /* Latin small letter e with acute */
    map.put((char)234, "ecirc");  /* Latin small letter e with circumflex */
    map.put((char)235, "euml"); /* Latin small letter e with diaeresis */
    map.put((char)236, "igrave"); /* Latin small letter i with grave */
    map.put((char)237, "iacute"); /* Latin small letter i with acute */
    map.put((char)238, "icirc");  /* Latin small letter i with circumflex */
    map.put((char)239, "iuml"); /* Latin small letter i with diaeresis */
    map.put((char)240, "eth");   /* Latin small letter eth */
    map.put((char)241, "ntilde"); /* Latin small letter n with tilde */
    map.put((char)242, "ograve"); /* Latin small letter o with grave */
    map.put((char)243, "oacute"); /* Latin small letter o with acute */
    map.put((char)244, "ocirc");  /* Latin small letter o with circumflex */
    map.put((char)245, "otilde"); /* Latin small letter o with tilde */
    map.put((char)246, "ouml"); /* Latin small letter o with diaeresis */
    map.put((char)247, "divide"); /* division sign */
    map.put((char)248, "oslash"); /* Latin small letter o with stroke */
    map.put((char)249, "ugrave"); /* Latin small letter u with grave */
    map.put((char)250, "uacute"); /* Latin small letter u with acute */
    map.put((char)251, "ucirc");  /* Latin small letter u with circumflex */
    map.put((char)252, "uuml"); /* Latin small letter u with diaeresis */
    map.put((char)253, "yacute"); /* Latin small letter y with acute */
    map.put((char)254, "thorn");  /* Latin small letter thorn */
    map.put((char)255, "yuml"); /* Latin small letter y with diaeresis */
    map.put((char)338, "OElig");  /* Latin capital ligature oe */
    map.put((char)339, "oelig");  /* Latin small ligature oe */
    map.put((char)352, "Scaron"); /* Latin capital letter s with caron */
    map.put((char)353, "scaron"); /* Latin small letter s with caron */
    map.put((char)376, "Yuml"); /* Latin capital letter y with diaeresis */
    map.put((char)402, "fnof"); /* Latin small letter f with hook */
    map.put((char)710, "circ"); /* modifier letter circumflex accent */
    map.put((char)732, "tilde");  /* small tilde */
    map.put((char)913, "Alpha");  /* Greek capital letter alpha */
    map.put((char)914, "Beta"); /* Greek capital letter beta */
    map.put((char)915, "Gamma");  /* Greek capital letter gamma */
    map.put((char)916, "Delta");  /* Greek capital letter delta */
    map.put((char)917, "Epsilon");  /* Greek capital letter epsilon */
    map.put((char)918, "Zeta"); /* Greek capital letter zeta */
    map.put((char)919, "Eta");   /* Greek capital letter eta */
    map.put((char)920, "Theta");  /* Greek capital letter theta */
    map.put((char)921, "Iota"); /* Greek capital letter iota */
    map.put((char)922, "Kappa");  /* Greek capital letter kappa */
    map.put((char)923, "Lambda"); /* Greek capital letter lambda */
    map.put((char)924, "Mu");  /* Greek capital letter mu */
    map.put((char)925, "Nu");  /* Greek capital letter nu */
    map.put((char)926, "Xi");  /* Greek capital letter xi */
    map.put((char)927, "Omicron");  /* Greek capital letter omicron */
    map.put((char)928, "Pi");  /* Greek capital letter pi */
    map.put((char)929, "Rho");   /* Greek capital letter rho */
    map.put((char)931, "Sigma");  /* Greek capital letter sigma */
    map.put((char)932, "Tau");   /* Greek capital letter tau */
    map.put((char)933, "Upsilon");  /* Greek capital letter upsilon */
    map.put((char)934, "Phi");   /* Greek capital letter phi */
    map.put((char)935, "Chi");   /* Greek capital letter chi */
    map.put((char)936, "Psi");   /* Greek capital letter psi */
    map.put((char)937, "Omega");  /* Greek capital letter omega */
    map.put((char)945, "alpha");  /* Greek small letter alpha */
    map.put((char)946, "beta"); /* Greek small letter beta */
    map.put((char)947, "gamma");  /* Greek small letter gamma */
    map.put((char)948, "delta");  /* Greek small letter delta */
    map.put((char)949, "epsilon");  /* Greek small letter epsilon */
    map.put((char)950, "zeta"); /* Greek small letter zeta */
    map.put((char)951, "eta");   /* Greek small letter eta */
    map.put((char)952, "theta");  /* Greek small letter theta */
    map.put((char)953, "iota"); /* Greek small letter iota */
    map.put((char)954, "kappa");  /* Greek small letter kappa */
    map.put((char)955, "lambda"); /* Greek small letter lambda */
    map.put((char)956, "mu");  /* Greek small letter mu */
    map.put((char)957, "nu");  /* Greek small letter nu */
    map.put((char)958, "xi");  /* Greek small letter xi */
    map.put((char)959, "omicron");  /* Greek small letter omicron */
    map.put((char)960, "pi");  /* Greek small letter pi */
    map.put((char)961, "rho");   /* Greek small letter rho */
    map.put((char)962, "sigmaf"); /* Greek small letter final sigma */
    map.put((char)963, "sigma");  /* Greek small letter sigma */
    map.put((char)964, "tau");   /* Greek small letter tau */
    map.put((char)965, "upsilon");  /* Greek small letter upsilon */
    map.put((char)966, "phi");   /* Greek small letter phi */
    map.put((char)967, "chi");   /* Greek small letter chi */
    map.put((char)968, "psi");   /* Greek small letter psi */
    map.put((char)969, "omega");  /* Greek small letter omega */
    map.put((char)977, "thetasym"); /* Greek theta symbol */
    map.put((char)978, "upsih");  /* Greek upsilon with hook symbol */
    map.put((char)982, "piv");   /* Greek pi symbol */
    map.put((char)8194,  "ensp"); /* en space */
    map.put((char)8195,  "emsp"); /* em space */
    map.put((char)8201,  "thinsp"); /* thin space */
    map.put((char)8204,  "zwnj"); /* zero width non-joiner */
    map.put((char)8205,  "zwj");   /* zero width joiner */
    map.put((char)8206,  "lrm");   /* left-to-right mark */
    map.put((char)8207,  "rlm");   /* right-to-left mark */
    map.put((char)8211,  "ndash");  /* en dash */
    map.put((char)8212,  "mdash");  /* em dash */
    map.put((char)8216,  "lsquo");  /* left single quotation mark */
    map.put((char)8217,  "rsquo");  /* right single quotation mark */
    map.put((char)8218,  "sbquo");  /* single low-9 quotation mark */
    map.put((char)8220,  "ldquo");  /* left double quotation mark */
    map.put((char)8221,  "rdquo");  /* right double quotation mark */
    map.put((char)8222,  "bdquo");  /* double low-9 quotation mark */
    map.put((char)8224,  "dagger"); /* dagger */
    map.put((char)8225,  "Dagger"); /* double dagger */
    map.put((char)8226,  "bull"); /* bullet */
    map.put((char)8230,  "hellip"); /* horizontal ellipsis */
    map.put((char)8240,  "permil"); /* per mille sign */
    map.put((char)8242,  "prime");  /* prime */
    map.put((char)8243,  "Prime");  /* double prime */
    map.put((char)8249,  "lsaquo"); /* single left-pointing angle quotation mark */
    map.put((char)8250,  "rsaquo"); /* single right-pointing angle quotation mark */
    map.put((char)8254,  "oline");  /* overline */
    map.put((char)8260,  "frasl");  /* fraction slash */
    map.put((char)8364,  "euro"); /* euro sign */
    map.put((char)8465,  "image");  /* black-letter capital i */
    map.put((char)8472,  "weierp"); /* script capital pXCOMMAX Weierstrass p */
    map.put((char)8476,  "real"); /* black-letter capital r */
    map.put((char)8482,  "trade");  /* trademark sign */
    map.put((char)8501,  "alefsym");  /* alef symbol */
    map.put((char)8592,  "larr"); /* leftwards arrow */
    map.put((char)8593,  "uarr"); /* upwards arrow */
    map.put((char)8594,  "rarr"); /* rightwards arrow */
    map.put((char)8595,  "darr"); /* downwards arrow */
    map.put((char)8596,  "harr"); /* left right arrow */
    map.put((char)8629,  "crarr");  /* downwards arrow with corner leftwards */
    map.put((char)8656,  "lArr"); /* leftwards double arrow */
    map.put((char)8657,  "uArr"); /* upwards double arrow */
    map.put((char)8658,  "rArr"); /* rightwards double arrow */
    map.put((char)8659,  "dArr"); /* downwards double arrow */
    map.put((char)8660,  "hArr"); /* left right double arrow */
    map.put((char)8704,  "forall"); /* for all */
    map.put((char)8706,  "part"); /* partial differential */
    map.put((char)8707,  "exist");  /* there exists */
    map.put((char)8709,  "empty");  /* empty set */
    map.put((char)8711,  "nabla");  /* nabla */
    map.put((char)8712,  "isin"); /* element of */
    map.put((char)8713,  "notin");  /* not an element of */
    map.put((char)8715,  "ni");  /* contains as member */
    map.put((char)8719,  "prod"); /* n-ary product */
    map.put((char)8721,  "sum");   /* n-ary summation */
    map.put((char)8722,  "minus");  /* minus sign */
    map.put((char)8727,  "lowast"); /* asterisk operator */
    map.put((char)8730,  "radic");  /* square root */
    map.put((char)8733,  "prop"); /* proportional to */
    map.put((char)8734,  "infin");  /* infinity */
    map.put((char)8736,  "ang");   /* angle */
    map.put((char)8743,  "and");   /* logical and */
    map.put((char)8744,  "or");  /* logical or */
    map.put((char)8745,  "cap");   /* intersection */
    map.put((char)8746,  "cup");   /* union */
    map.put((char)8747,  "int");   /* integral */
    map.put((char)8756,  "there4"); /* therefore */
    map.put((char)8764,  "sim");   /* tilde operator */
    map.put((char)8773,  "cong"); /* congruent to */
    map.put((char)8776,  "asymp");  /* almost equal to */
    map.put((char)8800,  "ne");  /* not equal to */
    map.put((char)8801,  "equiv");  /* identical toXCOMMAX equivalent to */
    map.put((char)8804,  "le");  /* less-than or equal to */
    map.put((char)8805,  "ge");  /* greater-than or equal to */
    map.put((char)8834,  "sub");   /* subset of */
    map.put((char)8835,  "sup");   /* superset of */
    map.put((char)8836,  "nsub"); /* not a subset of */
    map.put((char)8838,  "sube"); /* subset of or equal to */
    map.put((char)8839,  "supe"); /* superset of or equal to */
    map.put((char)8853,  "oplus");  /* circled plus */
    map.put((char)8855,  "otimes"); /* circled times */
    map.put((char)8869,  "perp"); /* up tack */
    map.put((char)8901,  "sdot"); /* dot operator */
    map.put((char)8968,  "lceil");  /* left ceiling */
    map.put((char)8969,  "rceil");  /* right ceiling */
    map.put((char)8970,  "lfloor"); /* left floor */
    map.put((char)8971,  "rfloor"); /* right floor */
    map.put((char)9001,  "lang"); /* left-pointing angle bracket */
    map.put((char)9002,  "rang"); /* right-pointing angle bracket */
    map.put((char)9674,  "loz");   /* lozenge */
    map.put((char)9824,  "spades"); /* black spade suit */
    map.put((char)9827,  "clubs");  /* black club suit */
    map.put((char)9829,  "hearts"); /* black heart suit */
    map.put((char)9830,  "diams");  /* black diamond suit */

    characterToEntityMap =  Collections.unmodifiableMap(map);

  }
}