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上一篇了解了Base64编码的原理，，下面是java的实现：public final class Base64 { private static final byte PAD = (byte) ‘=’; private static final int BASELENGTH = 255; private static final int LOOKUPLENGTH = 64; private static final int SIGN = -128;//8位全1 private static byte[] base64Alphabet = new byte[BASELENGTH]; private static byte[] lookUpBase64Alphabet = new byte[LOOKUPLENGTH]; // Populating the lookup and character arrays static { for (int i = 0; i < BASELENGTH; i++) { base64Alphabet[i] = (byte) -1; } for (int i = ‘Z’; i >= ‘A’; i–) { base64Alphabet[i] = (byte) (i – ‘A’); } for (int i = ‘z’; i >= ‘a’; i–) { base64Alphabet[i] = (byte) (i – ‘a’ + 26); } for (int i = ‘9’; i >= ‘0’; i–) { base64Alphabet[i] = (byte) (i – ‘0’ + 52); } base64Alphabet[‘+’] = 62; base64Alphabet[‘/’] = 63; for (int i = 0; i <= 25; i++) { lookUpBase64Alphabet[i] = (byte) (‘A’ + i); } for (int i = 26, j = 0; i <= 51; i++, j++) { lookUpBase64Alphabet[i] = (byte) (‘a’ + j); } for (int i = 52, j = 0; i <= 61; i++, j++) { lookUpBase64Alphabet[i] = (byte) (‘0’ + j); } lookUpBase64Alphabet[62] = (byte) ‘+’; lookUpBase64Alphabet[63] = (byte) ‘/’; } /** * Encodes binary data using the base64 algorithm, optionally chunking the output into 76 character blocks. * * @param binaryData Array containing binary data to encode. * @return Base64-encoded data. */ public static byte[] encodeBase64(byte[] binaryData) { int lengthDataBits = binaryData.length * 8; int fewerThan24bits = lengthDataBits % 24; int numberTriplets = lengthDataBits / 24; byte encodedData[] = null; int encodedDataLength = 0; if (fewerThan24bits != 0) { //data not divisible by 24 bit encodedDataLength = (numberTriplets + 1) * 4; } else { // 16 or 8 bit encodedDataLength = numberTriplets * 4; } encodedData = new byte[encodedDataLength]; byte k = 0, l = 0, b1 = 0, b2 = 0, b3 = 0; int encodedIndex = 0; int dataIndex = 0; int i = 0; //log.debug("number of triplets = " + numberTriplets); for (i = 0; i < numberTriplets; i++) { dataIndex = i * 3; b1 = binaryData[dataIndex]; b2 = binaryData[dataIndex + 1]; b3 = binaryData[dataIndex + 2]; //log.debug("b1= " + b1 +", b2= " + b2 + ", b3= " + b3); l = (byte) (b2 & 0x0f);//前4位 k = (byte) (b1 & 0x03);//前2位 byte val1 = ((b1 & SIGN) == 0) ? (byte) (b1 >> 2) : (byte) ((b1) >> 2 ^ 0xc0);//>>优先级高于^，取前6位 byte val2 = ((b2 & SIGN) == 0) ? (byte) (b2 >> 4) : (byte) ((b2) >> 4 ^ 0xf0);//取前4位 byte val3 = ((b3 & SIGN) == 0) ? (byte) (b3 >> 6) : (byte) ((b3) >> 6 ^ 0xfc);//取前2位 encodedData[encodedIndex] = lookUpBase64Alphabet[val1]; //log.debug( "val2 = " + val2 ); //log.debug( "k4 = " + (k<<4) ); //log.debug( "vak = " + (val2 | (k<<4)) ); encodedData[encodedIndex + 1] = lookUpBase64Alphabet[val2 | (k << 4)]; encodedData[encodedIndex + 2] = lookUpBase64Alphabet[(l << 2) | val3]; encodedData[encodedIndex + 3] = lookUpBase64Alphabet[b3 & 0x3f];//取最后6位 encodedIndex += 4; } // form integral number of 6-bit groups dataIndex = i * 3; if (fewerThan24bits == 8) { b1 = binaryData[dataIndex]; k = (byte) (b1 & 0x03); //log.debug("b1=" + b1); //log.debug("b1<<2 = " + (b1>>2) ); byte val1 = ((b1 & SIGN) == 0) ? (byte) (b1 >> 2) : (byte) ((b1) >> 2 ^ 0xc0); encodedData[encodedIndex] = lookUpBase64Alphabet[val1]; encodedData[encodedIndex + 1] = lookUpBase64Alphabet[k << 4]; encodedData[encodedIndex + 2] = PAD; encodedData[encodedIndex + 3] = PAD; } else if (fewerThan24bits == 16) { b1 = binaryData[dataIndex]; b2 = binaryData[dataIndex + 1]; l = (byte) (b2 & 0x0f); k = (byte) (b1 & 0x03); byte val1 = ((b1 & SIGN) == 0) ? (byte) (b1 >> 2) : (byte) ((b1) >> 2 ^ 0xc0); byte val2 = ((b2 & SIGN) == 0) ? (byte) (b2 >> 4) : (byte) ((b2) >> 4 ^ 0xf0); encodedData[encodedIndex] = lookUpBase64Alphabet[val1]; encodedData[encodedIndex + 1] = lookUpBase64Alphabet[val2 | (k << 4)]; encodedData[encodedIndex + 2] = lookUpBase64Alphabet[l << 2]; encodedData[encodedIndex + 3] = PAD; } return encodedData; } /** * Decodes Base64 data into octects * * @param base64Data Byte array containing Base64 data * @return Array containing decoded data. */ public static byte[] decodeBase64(byte[] base64Data) { // handle the edge case, so we don’t have to worry about it later if (base64Data.length == 0) { return new byte[0]; } int numberQuadruple = base64Data.length / 4; byte decodedData[] = null; byte b1 = 0, b2 = 0, b3 = 0, b4 = 0, marker0 = 0, marker1 = 0; // Throw away anything not in base64Data int encodedIndex = 0; int dataIndex = 0; { // this sizes the output array properly – rlw int lastData = base64Data.length; // ignore the ‘=’ padding while (base64Data[lastData – 1] == PAD) { if (–lastData == 0) { return new byte[0]; } } decodedData = new byte[lastData – numberQuadruple]; } for (int i = 0; i < numberQuadruple; i++) { dataIndex = i * 4; marker0 = base64Data[dataIndex + 2]; marker1 = base64Data[dataIndex + 3]; b1 = base64Alphabet[base64Data[dataIndex]]; b2 = base64Alphabet[base64Data[dataIndex + 1]]; if (marker0 != PAD && marker1 != PAD) { //No PAD e.g 3cQl b3 = base64Alphabet[marker0]; b4 = base64Alphabet[marker1]; decodedData[encodedIndex] = (byte) (b1 << 2 | b2 >> 4); decodedData[encodedIndex + 1] = (byte) (((b2 & 0xf) << 4) | ((b3 >> 2) & 0xf)); decodedData[encodedIndex + 2] = (byte) (b3 << 6 | b4); } else if (marker0 == PAD) { //Two PAD e.g. 3c[Pad][Pad] decodedData[encodedIndex] = (byte) (b1 << 2 | b2 >> 4); } else if (marker1 == PAD) { //One PAD e.g. 3cQ[Pad] b3 = base64Alphabet[marker0]; decodedData[encodedIndex] = (byte) (b1 << 2 | b2 >> 4); decodedData[encodedIndex + 1] = (byte) (((b2 & 0xf) << 4) | ((b3 >> 2) & 0xf)); } encodedIndex += 3; } return decodedData; }}

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