最近在Android上的一个项目中需要用到VCard的一些东西，发现其中有一部分关于Quoted-Printable编码的部分稍微有点棘手，主要是看起来规则比较复杂，在网上搜索一下中文翻译的都很简单，看原版E文的，又觉得有些晦涩。在一个开源项目中看到一个关于QuotedPrintable的类，但是只写了decode部分，我按照自己的理解把那个类补充了一下，加入了encode功能。

QP编码规则中关于空格和TAB部分，有点复杂，其实搞得人头晕，实际上可以简单处理，把空格和TAB也当做要转化成=XX格式的字符处理就ok了，就不用再去考虑空格和TAB在行尾的情况了。

在网上看了一些朋友的示例代码，但大多都没有处理76字符的行长度限制，我给加上了。

下面是代码：

import java.io.UnsupportedEncodingException; import android.util.Log; /** * A class containing static methods to perform decoding from <b>quoted * printable</b> content transfer encoding and to encode into */ public class QuotedPrintable { private final static byte TAB = 0x09; // /t private final static byte LF = 0x0A; // /n private final static byte CR = 0x0D; // /r private final static byte SPACE = 0x20; // ' ' private final static byte EQUALS = 0x3D; // '=' private final static byte LIT_START = 0x21; private final static byte LIT_END = 0x7e; private final static int MAX_LINE_LENGTH = 76; private static int mCurrentLineLength = 0; /** * A method to decode quoted printable encoded data. * It overrides the same input byte array to save memory. Can be done * because the result is surely smaller than the input. * * @param qp * a byte array to decode. * @return the length of the decoded array. */ public static int decode(byte [] qp) { int qplen = qp.length; int retlen = 0; for (int i=0; i < qplen; i++) { // Handle encoded chars if (qp[i] == '=') { if (qplen - i > 2) { // The sequence can be complete, check it if (qp[i+1] == CR && qp[i+2] == LF) { // soft line break, ignore it i += 2; continue; } else if (isHexDigit(qp[i+1]) && isHexDigit(qp[i+2]) ) { // convert the number into an integer, taking // the ascii digits stored in the array. qp[retlen++]=(byte)(getHexValue(qp[i+1])*16 + getHexValue(qp[i+2])); i += 2; continue; } else { Log.e("DEBUG", "decode: Invalid sequence = " + qp[i+1] + qp[i+2]); } } // In all wrong cases leave the original bytes // (see RFC 2045). They can be incomplete sequence, // or a '=' followed by non hex digit. } // RFC 2045 says to exclude control characters mistakenly // present (unencoded) in the encoded stream. // As an exception, we keep unencoded tabs (0x09) if( (qp[i] >= 0x20 && qp[i] <= 0x7f) || qp[i] == TAB || qp[i] == CR || qp[i] == LF) { qp[retlen++] = qp[i]; } } return retlen; } private static boolean isHexDigit(byte b) { return ( (b>=0x30 && b<=0x39) || (b>=0x41&&b<=0x46) ); } private static byte getHexValue(byte b) { return (byte)Character.digit((char)b, 16); } /** * * @param qp Byte array to decode * @param enc The character encoding of the returned string * @return The decoded string. */ public static String decode(byte[] qp, String enc) { int len=decode(qp); try { return new String(qp, 0, len, enc); } catch (UnsupportedEncodingException e) { return new String(qp, 0, len); } } /** * A method to encode data in quoted printable * * @param content * The string to be encoded * @param enc * The character encoding of the content string * @return The encoded string. If the content is null, return null. */ public static String encode(String content, String enc) { if (content == null) return null; byte[] str = null; try { str = content.getBytes(enc); } catch (UnsupportedEncodingException e) { str = content.getBytes(); } return encode(str); } /** * A method to encode data in quoted printable * * @param content * The byte array of the string to be encoded * @return The encoded string. If the content is null, return null. */ public static String encode(byte[] content) { if (content == null) return null; StringBuilder out = new StringBuilder(); mCurrentLineLength = 0; int requiredLength = 0; for (int index = 0; index < content.length; index++) { byte c = content[index]; if (c >= LIT_START && c <= LIT_END && c != EQUALS) { requiredLength = 1; checkLineLength(requiredLength, out); out.append((char)c); } else { requiredLength = 3; checkLineLength(requiredLength, out); out.append('='); out.append(String.format("%02X", c)); } } return out.toString(); } private static void checkLineLength(int required, StringBuilder out) { if (required + mCurrentLineLength > MAX_LINE_LENGTH - 1) { out.append("=/r/n"); mCurrentLineLength = required; } else mCurrentLineLength += required; } }