application/x-www-form-urlencoded
* MIME format.
* * The conversion process is the reverse of that used by the URLEncoder class. It is assumed * that all characters in the encoded string are one of the following: * "{@code a}" through "{@code z}", * "{@code A}" through "{@code Z}", * "{@code 0}" through "{@code 9}", and * "{@code -}", "{@code _}", * "{@code .}", and "{@code *}". The * character "{@code %}" is allowed but is interpreted * as the start of a special escaped sequence. *
* The following rules are applied in the conversion: * *
* There are two possible ways in which this decoder could deal with * illegal strings. It could either leave illegal characters alone or * it could throw an {@link java.lang.IllegalArgumentException}. * Which approach the decoder takes is left to the * implementation. * * @author Mark Chamness * @author Michael McCloskey * @since 1.2 */ public class URLDecoder { // The platform default encoding static String dfltEncName = URLEncoder.dfltEncName; /** * Decodes a {@code x-www-form-urlencoded} string. * The platform's default encoding is used to determine what characters * are represented by any consecutive sequences of the form * "{@code %xy}". * @param s the {@code String} to decode * @deprecated The resulting string may vary depending on the platform's * default encoding. Instead, use the decode(String,String) method * to specify the encoding. * @return the newly decoded {@code String} */ @Deprecated public static String decode(String s) { String str = null; try { str = decode(s, dfltEncName); } catch (UnsupportedEncodingException e) { // The system should always have the platform default } return str; } /** * Decodes an {@code application/x-www-form-urlencoded} string using * a specific encoding scheme. * *
* This method behaves the same as {@linkplain decode(String s, Charset charset)} * except that it will {@linkplain java.nio.charset.Charset#forName look up the charset} * using the given encoding name. * * @implNote This implementation will throw an {@link java.lang.IllegalArgumentException} * when illegal strings are encountered. * * @param s the {@code String} to decode * @param enc The name of a supported * character * encoding. * @return the newly decoded {@code String} * @throws UnsupportedEncodingException * If character encoding needs to be consulted, but * named character encoding is not supported * @see URLEncoder#encode(java.lang.String, java.lang.String) * @since 1.4 */ public static String decode(String s, String enc) throws UnsupportedEncodingException { if (enc.isEmpty()) { throw new UnsupportedEncodingException ("URLDecoder: empty string enc parameter"); } try { Charset charset = Charset.forName(enc); return decode(s, charset); } catch (IllegalCharsetNameException | UnsupportedCharsetException e) { throw new UnsupportedEncodingException(enc); } } /** * Decodes an {@code application/x-www-form-urlencoded} string using * a specific {@linkplain java.nio.charset.Charset Charset}. * The supplied charset is used to determine * what characters are represented by any consecutive sequences of the * form "{@code %xy}". *
* Note: The * World Wide Web Consortium Recommendation states that * UTF-8 should be used. Not doing so may introduce * incompatibilities. * * @implNote This implementation will throw an {@link java.lang.IllegalArgumentException} * when illegal strings are encountered. * * @param s the {@code String} to decode * @param charset the given charset * @return the newly decoded {@code String} * @throws NullPointerException if {@code s} or {@code charset} is {@code null} * @throws IllegalArgumentException if the implementation encounters illegal * characters * @see URLEncoder#encode(java.lang.String, java.nio.charset.Charset) * @since 10 */ public static String decode(String s, Charset charset) { Objects.requireNonNull(charset, "Charset"); boolean needToChange = false; int numChars = s.length(); StringBuilder sb = new StringBuilder(numChars > 500 ? numChars / 2 : numChars); int i = 0; char c; byte[] bytes = null; while (i < numChars) { c = s.charAt(i); switch (c) { case '+': sb.append(' '); i++; needToChange = true; break; case '%': /* * Starting with this instance of %, process all * consecutive substrings of the form %xy. Each * substring %xy will yield a byte. Convert all * consecutive bytes obtained this way to whatever * character(s) they represent in the provided * encoding. */ try { // (numChars-i)/3 is an upper bound for the number // of remaining bytes if (bytes == null) bytes = new byte[(numChars-i)/3]; int pos = 0; while ( ((i+2) < numChars) && (c=='%')) { int v = Integer.parseInt(s, i + 1, i + 3, 16); if (v < 0) throw new IllegalArgumentException( "URLDecoder: Illegal hex characters in escape " + "(%) pattern - negative value"); bytes[pos++] = (byte) v; i+= 3; if (i < numChars) c = s.charAt(i); } // A trailing, incomplete byte encoding such as // "%x" will cause an exception to be thrown if ((i < numChars) && (c=='%')) throw new IllegalArgumentException( "URLDecoder: Incomplete trailing escape (%) pattern"); sb.append(new String(bytes, 0, pos, charset)); } catch (NumberFormatException e) { throw new IllegalArgumentException( "URLDecoder: Illegal hex characters in escape (%) pattern - " + e.getMessage()); } needToChange = true; break; default: sb.append(c); i++; break; } } return (needToChange? sb.toString() : s); } }