package com.cheng.utils.security;
public final class Base64 {
/**
* Base64编码表。
*/
private static final char[] BASE64CODE = { 'A', 'B', 'C', 'D', 'E', 'F',
'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S',
'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',
'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's',
't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5',
'6', '7', '8', '9', '+', '/', };
/**
* Base64解码表。
*/
private static final byte[] BASE64DECODE = { -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, // 注意两个63，为兼容SMP，
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, 63,
-1,
63, // “/”和“-”都翻译成63。
52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, 0, -1, -1, -1,
0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13,
14, // 注意两个0：
15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1,
-1, // “A”和“=”都翻译成0。
-1, 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, -1, -1, -1, -1, -1, };
private static final int HEX_255 = 0x0000ff;
private static final int HEX_16515072 = 0xfc0000;
private static final int HEX_258048 = 0x3f000;
private static final int HEX_4032 = 0xfc0;
private static final int HEX_63 = 0x3f;
private static final int HEX_16711680 = 0xff0000;
private static final int HEX_65280 = 0x00ff00;
private static final int NUMBER_TWO = 2;
private static final int NUMBER_THREE = 3;
private static final int NUMBER_FOUR = 4;
private static final int NUMBER_SIX = 6;
private static final int NUMBER_EIGHT = 8;
private static final int NUMBER_TWELVE = 12;
private static final int NUMBER_SIXTEEN = 16;
private static final int NUMBER_EIGHTEEN = 18;
/**
* 构造方法私有化，防止实例化。
*/
private Base64() {
}
/**
* Base64编码。将字节数组中字节3个一组编码成4个可见字符。
*
* @param b
* 需要被编码的字节数据。
* @return 编码后的Base64字符串。
*/
public static String encode(byte[] b) {
int code = 0;
// 按实际编码后长度开辟内存，加快速度
StringBuffer sb = new StringBuffer(
((b.length - 1) / NUMBER_THREE) << NUMBER_TWO + NUMBER_FOUR);
// 进行编码
for (int i = 0; i < b.length; i++) {
code |= (b[i] << (NUMBER_SIXTEEN - i % NUMBER_THREE * NUMBER_EIGHT))
& (HEX_255 << (NUMBER_SIXTEEN - i % NUMBER_THREE
* NUMBER_EIGHT));
if (i % NUMBER_THREE == NUMBER_TWO || i == b.length - 1) {
sb.append(BASE64CODE[(code & HEX_16515072) >>> NUMBER_EIGHTEEN]);
sb.append(BASE64CODE[(code & HEX_258048) >>> NUMBER_TWELVE]);
sb.append(BASE64CODE[(code & HEX_4032) >>> NUMBER_SIX]);
sb.append(BASE64CODE[code & HEX_63]);
code = 0;
}
}
// 对于长度非3的整数倍的字节数组，编码前先补0，编码后结尾处编码用=代替，
// =的个数和短缺的长度一致，以此来标识出数据实际长度
if (b.length % NUMBER_THREE > 0) {
sb.setCharAt(sb.length() - 1, '=');
}
if (b.length % NUMBER_THREE == 1) {
sb.setCharAt(sb.length() - NUMBER_TWO, '=');
}
return sb.toString();
}
/**
* Base64解码。
*
* @param code
* 用Base64编码的ASCII字符串
* @return 解码后的字节数据
*/
public static byte[] decode(String code) {
// 检查参数合法性
if (code == null) {
return null;
}
int len = code.length();
if (len % NUMBER_FOUR != 0) {
throw new IllegalArgumentException(
"Base64 string length must be 4*n");
}
if (code.length() == 0) {
return new byte[0];
}
// 统计填充的等号个数
int pad = 0;
if (code.charAt(len - 1) == '=') {
pad++;
}
if (code.charAt(len - NUMBER_TWO) == '=') {
pad++;
}
// 根据填充等号的个数来计算实际数据长度
int retLen = len / NUMBER_FOUR * NUMBER_THREE - pad;
// 分配字节数组空间
byte[] ret = new byte[retLen];
// 查表解码
char ch1, ch2, ch3, ch4;
int i;
for (i = 0; i < len; i += NUMBER_FOUR) {
int j = i / NUMBER_FOUR * NUMBER_THREE;
ch1 = code.charAt(i);
ch2 = code.charAt(i + 1);
ch3 = code.charAt(i + NUMBER_TWO);
ch4 = code.charAt(i + NUMBER_THREE);
int tmp = (BASE64DECODE[ch1] << NUMBER_EIGHTEEN)
| (BASE64DECODE[ch2] << NUMBER_TWELVE)
| (BASE64DECODE[ch3] << NUMBER_SIX) | (BASE64DECODE[ch4]);
ret[j] = (byte) ((tmp & HEX_16711680) >> NUMBER_SIXTEEN);
if (i < len - NUMBER_FOUR) {
ret[j + 1] = (byte) ((tmp & HEX_65280) >> NUMBER_EIGHT);
ret[j + NUMBER_TWO] = (byte) ((tmp & HEX_255));
} else {
if (j + 1 < retLen) {
ret[j + 1] = (byte) ((tmp & HEX_65280) >> NUMBER_EIGHT);
}
if (j + NUMBER_TWO < retLen) {
ret[j + NUMBER_TWO] = (byte) ((tmp & HEX_255));
}
}
}
return ret;
}
}