Base64编码算法（Basic编码）之iharder算法源码解析
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import java.io.UnsupportedEncodingException;/** * Base64编码算法（Basic编码）之iharder算法源码解析 * （注：本人剔除了非核心方法，并对解码表DECODABET做了微量修改） * @author Robert Harder * @author rob@iharder.net * @version 2.1 */public class Base64{ private Base64() {}/* ******** P R I V A T E F I E L D S ******** */ /** The equals sign (=) as a byte. */ private final static byte EQUALS_SIGN = (byte)'='; private final static byte OTHER_BYTE = -1; // Indicates equals sign in encoding private final static String ENCODING = "UTF-8"; /** The 64 valid Base64 values. */ private final static byte[] ALPHABET; private final static byte[] _NATIVE_ALPHABET = { (byte)'A', (byte)'B', (byte)'C', (byte)'D', (byte)'E', (byte)'F', (byte)'G', (byte)'H', (byte)'I', (byte)'J', (byte)'K', (byte)'L', (byte)'M', (byte)'N', (byte)'O', (byte)'P', (byte)'Q', (byte)'R', (byte)'S', (byte)'T', (byte)'U', (byte)'V', (byte)'W', (byte)'X', (byte)'Y', (byte)'Z', (byte)'a', (byte)'b', (byte)'c', (byte)'d', (byte)'e', (byte)'f', (byte)'g', (byte)'h', (byte)'i', (byte)'j', (byte)'k', (byte)'l', (byte)'m', (byte)'n', (byte)'o', (byte)'p', (byte)'q', (byte)'r', (byte)'s', (byte)'t', (byte)'u', (byte)'v', (byte)'w', (byte)'x', (byte)'y', (byte)'z', (byte)'0', (byte)'1', (byte)'2', (byte)'3', (byte)'4', (byte)'5', (byte)'6', (byte)'7', (byte)'8', (byte)'9', (byte)'+', (byte)'/' }; /** * Translates a Base64 value to either its 6-bit reconstruction value * or a negative number indicating some other meaning. **/ private final static byte[] DECODABET = { -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, // 索引 43 对应'+','+'在base64编码表中的索引是62 -1, -1, -1, 63, // 索引 47 对应 '/','/'在base64编码表中的索引是63 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, // 索引48- 57对应0-9,这10个数字在base64编码表中的索引是52-61 -1, -1, -1, EQUALS_SIGN, // 索引61 对应 '=' -1, -1, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, // 索引65 - 77对应字母'A' 到 'M' 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, // 索引78 - 90对应字母'N' 到 'Z' -1, -1, -1, -1, -1, -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, // 索引 97 - 109对应字母'a' - 'm' 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51 // 索引110 - 122对应字母'n' - 'z' }; /** Determine which ALPHABET to use. */ static { byte[] __bytes; try { __bytes = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/".getBytes( ENCODING ); } catch (java.io.UnsupportedEncodingException use) { __bytes = _NATIVE_ALPHABET; // Fall back to native encoding } ALPHABET = __bytes; }/* ******** E N C O D I N G M E T H O D S ******** */ /** * numSigBytes的值是3、2、1 * * numSigBytes = 3,表示将source[srcOffset]、source[ srcOffset + 1]、source[ srcOffset + 2]这三个字节 * 转换成Base64的四个字节 * * * numSigBytes = 2,表示将source[srcOffset]、source[ srcOffset + 1]这两个字节转换成Base64的四个字节 * * * numSigBytes = 1,表示将source[srcOffset]这单个字节转换成Base64的四个字节 * * 转换得到的4个字节依次存储到 destination[destOffset]、destination[destOffset + 1]、 * destination[destOffset + 1]、destination[destOffset + 1] */ private static byte[] encode3to4( byte[] source, int srcOffset, int numSigBytes, byte[] destination, int destOffset) { // 1 2 3 // 01234567890123456789012345678901 Bit position // --------000000001111111122222222 Array position from threeBytes // --------| || || || | Six bit groups to index ALPHABET // >>18 >>12 >> 6 >> 0 Right shift necessary // 0x3f 0x3f 0x3f Additional AND // Create buffer with zero-padding if there are only one or two // significant bytes passed in the array. // We have to shift left 24 in order to flush out the 1's that appear // when Java treats a value as negative that is cast from a byte to an int. int inBuff = (numSigBytes > 0 ? ((source[srcOffset] << 24) >>> 8) : 0) | (numSigBytes > 1 ? ((source[srcOffset + 1] << 24) >>> 16) : 0) | (numSigBytes > 2 ? ((source[srcOffset + 2] << 24) >>> 24) : 0); switch (numSigBytes) { case 3: destination[destOffset] = ALPHABET[(inBuff >>> 18)]; destination[destOffset + 1] = ALPHABET[(inBuff >>> 12) & 0x3f]; destination[destOffset + 2] = ALPHABET[(inBuff >>> 6) & 0x3f]; destination[destOffset + 3] = ALPHABET[(inBuff) & 0x3f]; return destination; case 2: destination[destOffset] = ALPHABET[(inBuff >>> 18)]; destination[destOffset + 1] = ALPHABET[(inBuff >>> 12) & 0x3f]; destination[destOffset + 2] = ALPHABET[(inBuff >>> 6) & 0x3f]; destination[destOffset + 3] = EQUALS_SIGN; return destination; case 1: destination[destOffset] = ALPHABET[(inBuff >>> 18)]; destination[destOffset + 1] = ALPHABET[(inBuff >>> 12) & 0x3f]; destination[destOffset + 2] = EQUALS_SIGN; destination[destOffset + 3] = EQUALS_SIGN; return destination; default: return destination; } } public static String encodeBytes( byte[] source, int off, int len) { //在Base64编码规则下，原始字节数 : 编码后的字节数 = 3 : 4，这里求出编码后的字节数总数（不考虑余数） int len43 = len * 4 / 3; byte[] outBuff = new byte[ ( len43 ) + ( (len % 3) > 0 ? 4 : 0 ) // 如果原始字节数不是3的整数倍，多余的字节会被编码成为4个字节，所以还得加4 ]; int d = 0; int e = 0; int len2 = len - 2; for( ; d < len2; d+=3, e+=4 ) { encode3to4( source, d+off, 3, outBuff, e ); } if( d < len ) { encode3to4( source, d+off, len - d, outBuff, e ); e += 4; } try { return new String( outBuff, 0, e, ENCODING ); } catch (java.io.UnsupportedEncodingException uue) { return new String( outBuff, 0, e ); } } public static String encodeBytes( byte[] source ) { return encodeBytes(source, 0, source.length); } public static String encode(String s) { byte[] bytes; try { bytes = s.getBytes(ENCODING); } catch( java.io.UnsupportedEncodingException uee ) { bytes = s.getBytes(); } return encodeBytes(bytes); }/* ******** D E C O D I N G M E T H O D S ******** */ /** * 该方法将4个字节还原为三个字节 * @param source * @param srcOffset * @param destination * @param destOffset * @return */ private static int decode4to3( byte[] source, int srcOffset, byte[] destination, int destOffset ) { // Example: Dk== if( source[ srcOffset + 2] == EQUALS_SIGN ) { // Two ways to do the same thing. Don't know which way I like best. //int outBuff = ( ( DECODABET[ source[ srcOffset ] ] << 24 ) >>> 6 ) // | ( ( DECODABET[ source[ srcOffset + 1] ] << 24 ) >>> 12 ); int outBuff = ( ( DECODABET[ source[ srcOffset ] ] & 0xFF ) << 18 ) | ( ( DECODABET[ source[ srcOffset + 1] ] & 0xFF ) << 12 ); destination[ destOffset ] = (byte)( outBuff >>> 16 ); return 1; } // Example: DkL= else if( source[ srcOffset + 3 ] == EQUALS_SIGN ) { // Two ways to do the same thing. Don't know which way I like best. //int outBuff = ( ( DECODABET[ source[ srcOffset ] ] << 24 ) >>> 6 ) // | ( ( DECODABET[ source[ srcOffset + 1 ] ] << 24 ) >>> 12 ) // | ( ( DECODABET[ source[ srcOffset + 2 ] ] << 24 ) >>> 18 ); int outBuff = ( ( DECODABET[ source[ srcOffset ] ] & 0xFF ) << 18 ) | ( ( DECODABET[ source[ srcOffset + 1 ] ] & 0xFF ) << 12 ) | ( ( DECODABET[ source[ srcOffset + 2 ] ] & 0xFF ) << 6 ); destination[ destOffset ] = (byte)( outBuff >>> 16 ); destination[ destOffset + 1 ] = (byte)( outBuff >>> 8 ); return 2; } // Example: DkLE else { try{ // Two ways to do the same thing. Don't know which way I like best. //int outBuff = ( ( DECODABET[ source[ srcOffset ] ] << 24 ) >>> 6 ) // | ( ( DECODABET[ source[ srcOffset + 1 ] ] << 24 ) >>> 12 ) // | ( ( DECODABET[ source[ srcOffset + 2 ] ] << 24 ) >>> 18 ) // | ( ( DECODABET[ source[ srcOffset + 3 ] ] << 24 ) >>> 24 ); int outBuff = ( ( DECODABET[ source[ srcOffset ] ] & 0xFF ) << 18 ) | ( ( DECODABET[ source[ srcOffset + 1 ] ] & 0xFF ) << 12 ) | ( ( DECODABET[ source[ srcOffset + 2 ] ] & 0xFF ) << 6) | ( ( DECODABET[ source[ srcOffset + 3 ] ] & 0xFF ) ); destination[ destOffset ] = (byte)( outBuff >> 16 ); destination[ destOffset + 1 ] = (byte)( outBuff >> 8 ); destination[ destOffset + 2 ] = (byte)( outBuff ); return 3; }catch( Exception e){ System.out.println(""+source[srcOffset]+ ": " + ( DECODABET[ source[ srcOffset ] ] ) ); System.out.println(""+source[srcOffset+1]+ ": " + ( DECODABET[ source[ srcOffset + 1 ] ] ) ); System.out.println(""+source[srcOffset+2]+ ": " + ( DECODABET[ source[ srcOffset + 2 ] ] ) ); System.out.println(""+source[srcOffset+3]+ ": " + ( DECODABET[ source[ srcOffset + 3 ] ] ) ); return -1; } } } public static byte[] decode( byte[] source, int off, int len ) { //在Base64编码规则下，原始字节数 : 编码后的字节数 = 3 : 4，这里估算解码后的字节数总数 int len34 = len * 3 / 4; byte[] outBuff = new byte[ len34 ]; // Upper limit on size of output, outBuff用于存放解码后的字节 int outBuffPosn = 0; byte[] b4 = new byte[4]; int b4Posn = 0; int i = 0; byte sbiCrop = 0; byte sbiDecode = 0; for( i = off; i < off + len; i++ ) { sbiCrop = (byte)(source[i] & 0x7f); // Only the low seven bits sbiDecode = DECODABET[sbiCrop ]; if(sbiDecode != OTHER_BYTE) { b4[ b4Posn++ ] = sbiCrop; if( b4Posn > 3 ) { outBuffPosn += decode4to3( b4, 0, outBuff, outBuffPosn ); b4Posn = 0; // If that was the equals sign, break out of 'for' loop if( sbiCrop == EQUALS_SIGN ) break; } } else { System.err.println( "Bad Base64 input character at " + i + ": " + source[i] + "(decimal)" ); return null; } } byte[] out = new byte[ outBuffPosn ]; System.arraycopy( outBuff, 0, out, 0, outBuffPosn ); return out; } public static byte[] decode(String s) { byte[] bytes; try { bytes = s.getBytes(ENCODING); } catch( java.io.UnsupportedEncodingException uee ) { bytes = s.getBytes(); } bytes = decode( bytes, 0, bytes.length ); return bytes; }/* ******** TEST M E T H O D S ******** */ public static void main(String... args) throws UnsupportedEncodingException { String str = "我是中国人!@#$%^&*()_+S【】；0987655.、，；‘、】【屏"; String enstr = encode(str); System.out.println(enstr); byte[] debytes = decode(enstr); String destr = new String( debytes, 0, debytes.length, ENCODING ); System.out.println(destr); }}阅读全文
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