RAS

package com.byd;

public class Base {
static private final int BASELENGTH = 255;
static private final int LOOKUPLENGTH = 64;
static private final int TWENTYFOURBITGROUP = 24;
static private final int EIGHTBIT = 8;
static private final int SIXTEENBIT = 16;
static private final int SIXBIT = 6;
static private final int FOURBYTE = 4;
static private final int SIGN = -128;
static private final byte PAD = (byte) '=';
static private byte [] base64Alphabet = new byte[BASELENGTH];
static private byte [] lookUpBase64Alphabet = new byte[LOOKUPLENGTH];

static
{
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] = (byte) '+';
lookUpBase64Alphabet[63] = (byte) '/';
}

public static boolean isBase64( String isValidString )
{
return isArrayByteBase64(isValidString.getBytes());
}

public static boolean isBase64( byte octect )
{
return (octect == PAD || base64Alphabet[octect] != -1);
}

public static boolean isArrayByteBase64( byte[] arrayOctect )
{
int length = arrayOctect.length;
if (length == 0)
{
return true;
}
for (int i=0; i < length; i++)
{
if(!Base.isBase64(arrayOctect[i]))
return false;
}
return true;
}
/**
* @author
* @param args
* @return
*/
public static String encode(String args){
return new String(encode(args.getBytes()));
}

/**
* Encodes hex octects into Base64.
*
* @param binaryData Array containing binary data to encode.
* @return Base64-encoded data.
*/
public static byte[] encode( byte[] binaryData )
{
int lengthDataBits = binaryData.length*EIGHTBIT;
int fewerThan24bits = lengthDataBits%TWENTYFOURBITGROUP;
int numberTriplets = lengthDataBits/TWENTYFOURBITGROUP;
byte encodedData[] = null;


if (fewerThan24bits != 0)
{
encodedData = new byte[ (numberTriplets + 1 ) * 4 ];
}
else
{
encodedData = new byte[ numberTriplets * 4 ];
}

byte k = 0, l = 0, b1 = 0, b2 = 0, b3 = 0;

int encodedIndex = 0;
int dataIndex = 0;
int i = 0;
for ( i = 0; i<numberTriplets; i++ )
{
dataIndex = i*3;
b1 = binaryData[dataIndex];
b2 = binaryData[dataIndex + 1];
b3 = binaryData[dataIndex + 2];

l = (byte)(b2 & 0x0f);
k = (byte)(b1 & 0x03);

encodedIndex = i * 4;
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+1] =
lookUpBase64Alphabet[ val2 | ( k<<4 )];
encodedData[encodedIndex+2] =
lookUpBase64Alphabet[ (l <<2 ) | val3 ];
encodedData[encodedIndex+3] = lookUpBase64Alphabet[ b3 & 0x3f ];
}

dataIndex = i*3;
encodedIndex = i*4;
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 + 1] = lookUpBase64Alphabet[ k<<4 ];
encodedData[encodedIndex + 2] = PAD;
encodedData[encodedIndex + 3] = 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 + 1] =
lookUpBase64Alphabet[ val2 | ( k<<4 )];
encodedData[encodedIndex + 2] = lookUpBase64Alphabet[ l<<2 ];
encodedData[encodedIndex + 3] = PAD;
}

return encodedData;
}

/**
* @author wangxiuwei
           * @param args
* @return
*/
public static String decode(String args){
return new String(decode(args.getBytes()));
}

/**
* Decodes Base64 data into octects
*
* @param base64Data Byte array containing Base64 data
* @return Array containing decoded data.
*/
public static byte[] decode( byte[] base64Data )
{
if(base64Data.length == 0) { return new byte[0]; }

int numberQuadruple = base64Data.length/FOURBYTE;
byte decodedData[] = null;
byte b1=0,b2=0,b3=0, b4=0, marker0=0, marker1=0;


int encodedIndex = 0;
int dataIndex = 0;
{
int lastData = base64Data.length;
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)
{
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)
{
decodedData[encodedIndex] = (byte)( b1 <<2 | b2>>4 ) ;
}
else if (marker1 == 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;
}
}
测试类
package com.byd;

public class test {

public static void main(String[] args) {
   String a="赚钱给狗狗买肉吃";
   Base test=new Base();
       String b=test.encode(a);
       System.out.println(b);
   String c=test.decode(b);
   System.out.println(c);

}

}
打印结果：6LWa6ZKx57uZ54uX54uX5Lmw6IKJ5ZCD
赚钱给狗狗买肉吃