base64 编解码的 Java 实现

/**
* Base64Util for Java
* cheungmine
* 2009-11-8
*/
public class Base64Util {
/**
* @param args
*/
public static void main(String[] args)
{
// 源字节数组
int cb = 0;
System.out.print("源字节数组: ");

byte in[] = new byte[100];
in[cb++]='1';
in[cb++]='2';
in[cb++]='3';
in[cb++]='4';
in[cb++]='5';

System.out.write(in, 0, cb);

// 计算编码需要的输出字节尺寸
int cbOut = encodeString( in, cb, null, 0);

// 为输出分配数组
byte out[] = new byte[cbOut];

// 开始编码
encodeString( in, cb, out, 0);

// 输出编码内容
System.out.print("\n编码后内容: ");
System.out.write(out, 0, cbOut);

// 计算解码需要的字节
int cbDec = decodeString(out, cbOut, null);

// 分配解码数组
byte dec[] = new byte[cbDec];

// 开始解码
decodeString(out, cbOut, dec);

// 输出解码结果, 这个结果和输出应该一致
System.out.print("\n解码的结果: ");
System.out.write(dec, 0, cbDec);
}

/**
* Translation Table as described in RFC1113
*/
static String cb64="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
/**
* Translation Table to decode (created by author)
*/
static String cd64="|$$$}rstuvwxyz{$$$$$$$>?@ABCDEFGHIJKLMNOPQRSTUVW$$$$$$XYZ[\\]^_`abcdefghijklmnopq";
/**
* encodeBlock
*
* encode 3 8-bit binary bytes (in) as 4 '6-bit' characters (out)
*/
static void encodeBlock( byte in[], byte out[], int len )
{
out[0] = (byte) cb64.charAt( in[0] >> 2 );
out[1] = (byte) cb64.charAt( ((in[0] & 0x03) << 4) | ((in[1] & 0xf0) >> 4) );
out[2] = (byte) (len > 1 ? cb64.charAt( ((in[1] & 0x0f) << 2) | ((in[2] & 0xc0) >> 6) ) : '=');
out[3] = (byte) (len > 2 ? cb64.charAt( in[2] & 0x3f ) : '=');
}

/**
* decodeBlock
*
* decode 4 '6-bit' characters into 3 8-bit binary bytes
*/