Base64是网络上最常见的用于传输8Bit字节代码的编码方式之一，大家可以查看RFC2045～RFC2049，上面有MIME的详细规范。Base64编码可用于在HTTP环境下传递较长的标识信息。例如，在Java Persistence系统hibernate 中，就采用了Base64来将一个较长的唯一标识符（一般为128-bit的UUID）编码为一个字符串，用作HTTP表单和HTTP GET URL中的参数。在其他应用程序中，也常常需要把二进制数据编码为适合放在URL（包括隐藏表单域）中的形式。此时，采用Base64编码具有不可读性，即所编码的数据不会被人用肉眼所直接看到。
package com.jianggujin.codec;
/**
* Base64
*
* @author jianggujin
*
*/
public class HQBase64
{private final byte [] EMPTY = new byte [0 ];
private final int BASELENGTH = 128 ;
private final int LOOKUPLENGTH = 64 ;
private final int TWENTYFOURBITGROUP = 24 ;
private final int EIGHTBIT = 8 ;
private final int SIXTEENBIT = 16 ;
private final int FOURBYTE = 4 ;
private final int SIGN = -128 ;
private final char PAD = '=' ;
private final byte [] base64Alphabet = new byte [BASELENGTH];
private final byte [] lookUpBase64Alphabet = new byte [LOOKUPLENGTH];
private static HQBase64 base64 = new HQBase64();
public static HQBase64 getInstance ()
{
return base64;
}
private HQBase64 ()
{
for (int i = 0 ; i < BASELENGTH; ++i)
{
base64Alphabet[i] = -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 ] = (char ) '+' ;
lookUpBase64Alphabet[63 ] = (char ) '/' ;
}
private boolean isWhiteSpace (byte octect)
{
return (octect == 0x20 || octect == 0xd || octect == 0xa || octect == 0x9 );
}
private boolean isPad (byte octect)
{
return (octect == PAD);
}
private boolean isData (byte octect)
{
return (octect < BASELENGTH && base64Alphabet[octect] != -1 );
}
private int removeWhiteSpace (byte [] data)
{
if (data == null )
{
return 0 ;
}
int newSize = 0 ;
int len = data.length;
for (int i = 0 ; i < len; i++)
{
if (!isWhiteSpace(data[i]))
{
data[newSize++] = data[i];
}
}
return newSize;
}
public byte [] encode (byte [] binaryData)
{
if (binaryData == null )
{
return null ;
}
int lengthDataBits = binaryData.length * EIGHTBIT;
if (lengthDataBits == 0 )
{
return EMPTY;
}
int fewerThan24bits = lengthDataBits % TWENTYFOURBITGROUP;
int numberTriplets = lengthDataBits / TWENTYFOURBITGROUP;
int numberQuartet = fewerThan24bits != 0 ? numberTriplets + 1 : numberTriplets;
byte encodedData[] = null ;
encodedData = new byte [numberQuartet * 4 ];
byte k = 0 , l = 0 , b1 = 0 , b2 = 0 , b3 = 0 ;
int encodedIndex = 0 ;
int dataIndex = 0 ;
for (int i = 0 ; i < numberTriplets; i++)
{
b1 = binaryData[dataIndex++];
b2 = binaryData[dataIndex++];
b3 = binaryData[dataIndex++];
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 );
byte val3 = ((b3 & SIGN) == 0 ) ? (byte ) (b3 >> 6 ) : (byte ) ((b3) >> 6 ^ 0xfc );
encodedData[encodedIndex++] = lookUpBase64Alphabet[val1];
encodedData[encodedIndex++] = lookUpBase64Alphabet[val2 | (k << 4 )];
encodedData[encodedIndex++] = lookUpBase64Alphabet[(l << 2 ) | val3];
encodedData[encodedIndex++] = lookUpBase64Alphabet[b3 & 0x3f ];
}
if (fewerThan24bits == EIGHTBIT)
{
b1 = binaryData[dataIndex];
k = (byte ) (b1 & 0x03 );
byte val1 = ((b1 & SIGN) == 0 ) ? (byte ) (b1 >> 2 ) : (byte ) ((b1) >> 2 ^ 0xc0 );
encodedData[encodedIndex++] = lookUpBase64Alphabet[val1];
encodedData[encodedIndex++] = lookUpBase64Alphabet[k << 4 ];
encodedData[encodedIndex++] = PAD;
encodedData[encodedIndex++] = PAD;
}
else if (fewerThan24bits == SIXTEENBIT)
{
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++] = lookUpBase64Alphabet[val2 | (k << 4 )];
encodedData[encodedIndex++] = lookUpBase64Alphabet[l << 2 ];
encodedData[encodedIndex++] = PAD;
}
return encodedData;
}
public byte [] decode (byte [] encoded)
{
if (encoded == null )
{
return null ;
}
byte [] base64Data = encoded;
int len = removeWhiteSpace(base64Data);
if (len % FOURBYTE != 0 )
{
return null ;
}
int numberQuadruple = (len / FOURBYTE);
if (numberQuadruple == 0 )
{
return new byte [0 ];
}
byte decodedData[] = null ;
byte b1 = 0 , b2 = 0 , b3 = 0 , b4 = 0 ;
byte d1 = 0 , d2 = 0 , d3 = 0 , d4 = 0 ;
int i = 0 ;
int encodedIndex = 0 ;
int dataIndex = 0 ;
decodedData = new byte [(numberQuadruple) * 3 ];
for (; i < numberQuadruple - 1 ; i++)
{
if (!isData((d1 = base64Data[dataIndex++])) || !isData((d2 = base64Data[dataIndex++]))
|| !isData((d3 = base64Data[dataIndex++])) || !isData((d4 = base64Data[dataIndex++])))
{
return null ;
}
b1 = base64Alphabet[d1];
b2 = base64Alphabet[d2];
b3 = base64Alphabet[d3];
b4 = base64Alphabet[d4];
decodedData[encodedIndex++] = (byte ) (b1 << 2 | b2 >> 4 );
decodedData[encodedIndex++] = (byte ) (((b2 & 0xf ) << 4 ) | ((b3 >> 2 ) & 0xf ));
decodedData[encodedIndex++] = (byte ) (b3 << 6 | b4);
}
if (!isData((d1 = base64Data[dataIndex++])) || !isData((d2 = base64Data[dataIndex++])))
{
return null ;
}
b1 = base64Alphabet[d1];
b2 = base64Alphabet[d2];
d3 = base64Data[dataIndex++];
d4 = base64Data[dataIndex++];
if (!isData((d3)) || !isData((d4)))
{
if (isPad(d3) && isPad(d4))
{
if ((b2 & 0xf ) != 0 )
{
return null ;
}
byte [] tmp = new byte [i * 3 + 1 ];
System.arraycopy(decodedData, 0 , tmp, 0 , i * 3 );
tmp[encodedIndex] = (byte ) (b1 << 2 | b2 >> 4 );
return tmp;
}
else if (!isPad(d3) && isPad(d4))
{
b3 = base64Alphabet[d3];
if ((b3 & 0x3 ) != 0 )
{
return null ;
}
byte [] tmp = new byte [i * 3 + 2 ];
System.arraycopy(decodedData, 0 , tmp, 0 , i * 3 );
tmp[encodedIndex++] = (byte ) (b1 << 2 | b2 >> 4 );
tmp[encodedIndex] = (byte ) (((b2 & 0xf ) << 4 ) | ((b3 >> 2 ) & 0xf ));
return tmp;
}
else
{
return null ;
}
}
else
{
b3 = base64Alphabet[d3];
b4 = base64Alphabet[d4];
decodedData[encodedIndex++] = (byte ) (b1 << 2 | b2 >> 4 );
decodedData[encodedIndex++] = (byte ) (((b2 & 0xf ) << 4 ) | ((b3 >> 2 ) & 0xf ));
decodedData[encodedIndex++] = (byte ) (b3 << 6 | b4);
}
return decodedData;
}
public String encodeToString (byte [] binaryData)
{
return new String(encode(binaryData));
}
public String encodeToString (String data)
{
return new String(encode(data.getBytes()));
}
public byte [] decodeString (String encoded)
{
return decode(encoded.getBytes());
}
}1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 编写一个测试 类来测试一下：
import org.junit.Test;
import com.jianggujin.codec.HQBase64;
public class Base64Test
{@Test
public void encode ()
{
byte [] data = "jianggujin" .getBytes();
String result = base64.encodeToString(data);
System.err.println(result);
System.err.println(new String(base64.decodeString(result)));
}
}1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 运行结果：
本文介绍了Base64编码的基本原理及其实现方法，并通过一个Java示例展示了如何进行Base64编码与解码操作。
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