Java tutorial
/* * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You under the Apache License, Version 2.0 * (the "License"); you may not use this file except in compliance with * the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package com.chukong.sdk.serv.support; import java.io.ByteArrayOutputStream; import java.io.IOException; import java.io.UnsupportedEncodingException; import java.util.HashMap; import java.util.Locale; import java.util.Map; import org.apache.http.ParseException; /** * Utility class to decode MIME texts. * * @since 1.3 */ public final class MimeUtility { /** * The {@code US-ASCII} charset identifier constant. */ private static final String US_ASCII_CHARSET = "US-ASCII"; /** * The marker to indicate text is encoded with BASE64 algorithm. */ private static final String BASE64_ENCODING_MARKER = "B"; /** * The marker to indicate text is encoded with QuotedPrintable algorithm. */ private static final String QUOTEDPRINTABLE_ENCODING_MARKER = "Q"; /** * If the text contains any encoded tokens, those tokens will be marked with "=?". */ private static final String ENCODED_TOKEN_MARKER = "=?"; /** * If the text contains any encoded tokens, those tokens will terminate with "=?". */ private static final String ENCODED_TOKEN_FINISHER = "?="; /** * The linear whitespace chars sequence. */ private static final String LINEAR_WHITESPACE = " \t\r\n"; /** * Mappings between MIME and Java charset. */ private static final Map<String, String> MIME2JAVA = new HashMap<String, String>(); static { MIME2JAVA.put("iso-2022-cn", "ISO2022CN"); MIME2JAVA.put("iso-2022-kr", "ISO2022KR"); MIME2JAVA.put("utf-8", "UTF8"); MIME2JAVA.put("utf8", "UTF8"); MIME2JAVA.put("ja_jp.iso2022-7", "ISO2022JP"); MIME2JAVA.put("ja_jp.eucjp", "EUCJIS"); MIME2JAVA.put("euc-kr", "KSC5601"); MIME2JAVA.put("euckr", "KSC5601"); MIME2JAVA.put("us-ascii", "ISO-8859-1"); MIME2JAVA.put("x-us-ascii", "ISO-8859-1"); } /** * Hidden constructor, this class must not be instantiated. */ private MimeUtility() { // do nothing } /** * Decode a string of text obtained from a mail header into * its proper form. The text generally will consist of a * string of tokens, some of which may be encoded using * base64 encoding. * * @param text The text to decode. * * @return The decoded text string. * @throws UnsupportedEncodingException if the detected encoding in the input text is not supported. */ public static String decodeText(String text) throws UnsupportedEncodingException { // if the text contains any encoded tokens, those tokens will be marked with "=?". If the // source string doesn't contain that sequent, no decoding is required. if (text.indexOf(ENCODED_TOKEN_MARKER) < 0) { return text; } int offset = 0; int endOffset = text.length(); int startWhiteSpace = -1; int endWhiteSpace = -1; StringBuilder decodedText = new StringBuilder(text.length()); boolean previousTokenEncoded = false; while (offset < endOffset) { char ch = text.charAt(offset); // is this a whitespace character? if (LINEAR_WHITESPACE.indexOf(ch) != -1) { // whitespace found startWhiteSpace = offset; while (offset < endOffset) { // step over the white space characters. ch = text.charAt(offset); if (LINEAR_WHITESPACE.indexOf(ch) != -1) { // whitespace found offset++; } else { // record the location of the first non lwsp and drop down to process the // token characters. endWhiteSpace = offset; break; } } } else { // we have a word token. We need to scan over the word and then try to parse it. int wordStart = offset; while (offset < endOffset) { // step over the non white space characters. ch = text.charAt(offset); if (LINEAR_WHITESPACE.indexOf(ch) == -1) { // not white space offset++; } else { break; } //NB: Trailing whitespace on these header strings will just be discarded. } // pull out the word token. String word = text.substring(wordStart, offset); // is the token encoded? decode the word if (word.startsWith(ENCODED_TOKEN_MARKER)) { try { // if this gives a parsing failure, treat it like a non-encoded word. String decodedWord = decodeWord(word); // are any whitespace characters significant? Append 'em if we've got 'em. if (!previousTokenEncoded && startWhiteSpace != -1) { decodedText.append(text.substring(startWhiteSpace, endWhiteSpace)); startWhiteSpace = -1; } // this is definitely a decoded token. previousTokenEncoded = true; // and add this to the text. decodedText.append(decodedWord); // we continue parsing from here...we allow parsing errors to fall through // and get handled as normal text. continue; } catch (ParseException e) { // just ignore it, skip to next word } } // this is a normal token, so it doesn't matter what the previous token was. Add the white space // if we have it. if (startWhiteSpace != -1) { decodedText.append(text.substring(startWhiteSpace, endWhiteSpace)); startWhiteSpace = -1; } // this is not a decoded token. previousTokenEncoded = false; decodedText.append(word); } } return decodedText.toString(); } /** * Parse a string using the RFC 2047 rules for an "encoded-word" * type. This encoding has the syntax: * * encoded-word = "=?" charset "?" encoding "?" encoded-text "?=" * * @param word The possibly encoded word value. * * @return The decoded word. * @throws ParseException * @throws UnsupportedEncodingException */ private static String decodeWord(String word) throws ParseException, UnsupportedEncodingException { // encoded words start with the characters "=?". If this not an encoded word, we throw a // ParseException for the caller. if (!word.startsWith(ENCODED_TOKEN_MARKER)) { throw new ParseException("Invalid RFC 2047 encoded-word: " + word); } int charsetPos = word.indexOf('?', 2); if (charsetPos == -1) { throw new ParseException("Missing charset in RFC 2047 encoded-word: " + word); } // pull out the character set information (this is the MIME name at this point). String charset = word.substring(2, charsetPos).toLowerCase(); // now pull out the encoding token the same way. int encodingPos = word.indexOf('?', charsetPos + 1); if (encodingPos == -1) { throw new ParseException("Missing encoding in RFC 2047 encoded-word: " + word); } String encoding = word.substring(charsetPos + 1, encodingPos); // and finally the encoded text. int encodedTextPos = word.indexOf(ENCODED_TOKEN_FINISHER, encodingPos + 1); if (encodedTextPos == -1) { throw new ParseException("Missing encoded text in RFC 2047 encoded-word: " + word); } String encodedText = word.substring(encodingPos + 1, encodedTextPos); // seems a bit silly to encode a null string, but easy to deal with. if (encodedText.length() == 0) { return ""; } try { // the decoder writes directly to an output stream. ByteArrayOutputStream out = new ByteArrayOutputStream(encodedText.length()); byte[] encodedData = encodedText.getBytes(US_ASCII_CHARSET); // Base64 encoded? if (encoding.equals(BASE64_ENCODING_MARKER)) { Base64Decoder.decode(encodedData, out); } else if (encoding.equals(QUOTEDPRINTABLE_ENCODING_MARKER)) { // maybe quoted printable. QuotedPrintableDecoder.decode(encodedData, out); } else { throw new UnsupportedEncodingException("Unknown RFC 2047 encoding: " + encoding); } // get the decoded byte data and convert into a string. byte[] decodedData = out.toByteArray(); return new String(decodedData, javaCharset(charset)); } catch (IOException e) { throw new UnsupportedEncodingException("Invalid RFC 2047 encoding"); } } /** * Translate a MIME standard character set name into the Java * equivalent. * * @param charset The MIME standard name. * * @return The Java equivalent for this name. */ private static String javaCharset(String charset) { // nothing in, nothing out. if (charset == null) { return null; } String mappedCharset = MIME2JAVA.get(charset.toLowerCase(Locale.ENGLISH)); // if there is no mapping, then the original name is used. Many of the MIME character set // names map directly back into Java. The reverse isn't necessarily true. if (mappedCharset == null) { return charset; } return mappedCharset; } }