net.vvakame.zaim4j.Base64 Maven / Gradle / Ivy

Go to download
package net.vvakame.zaim4j;

/**
 * Base64 conversion.
 * @author vvakame
 */
// from https://gist.github.com/dsiebel/898257
class Base64 {

	private final static char[] ALPHABET =
			"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/".toCharArray();

	private static int[] toInt = new int[128];

	static {
		for (int i = 0; i < ALPHABET.length; i++) {
			toInt[ALPHABET[i]] = i;
		}
	}


	/**
	 * Translates the specified byte array into Base64 string.
	 *
	 * @param buf the byte array (not null)
	 * @return the translated Base64 string (not null)
	 */
	public static String encode(byte[] buf) {
		int size = buf.length;
		char[] ar = new char[((size + 2) / 3) * 4];
		int a = 0;
		int i = 0;
		while (i < size) {
			byte b0 = buf[i++];
			byte b1 = (i < size) ? buf[i++] : 0;
			byte b2 = (i < size) ? buf[i++] : 0;

			int mask = 0x3F;
			ar[a++] = ALPHABET[(b0 >> 2) & mask];
			ar[a++] = ALPHABET[((b0 << 4) | ((b1 & 0xFF) >> 4)) & mask];
			ar[a++] = ALPHABET[((b1 << 2) | ((b2 & 0xFF) >> 6)) & mask];
			ar[a++] = ALPHABET[b2 & mask];
		}
		switch (size % 3) {
			case 1:
				ar[--a] = '=';
			case 2:
				ar[--a] = '=';
		}
		return new String(ar);
	}

	/**
	 * Translates the specified Base64 string into a byte array.
	 *
	 * @param s the Base64 string (not null)
	 * @return the byte array (not null)
	 */
	public static byte[] decode(String s) {
		int delta = s.endsWith("==") ? 2 : s.endsWith("=") ? 1 : 0;
		byte[] buffer = new byte[s.length() * 3 / 4 - delta];
		int mask = 0xFF;
		int index = 0;
		for (int i = 0; i < s.length(); i += 4) {
			int c0 = toInt[s.charAt(i)];
			int c1 = toInt[s.charAt(i + 1)];
			buffer[index++] = (byte) (((c0 << 2) | (c1 >> 4)) & mask);
			if (index >= buffer.length) {
				return buffer;
			}
			int c2 = toInt[s.charAt(i + 2)];
			buffer[index++] = (byte) (((c1 << 4) | (c2 >> 2)) & mask);
			if (index >= buffer.length) {
				return buffer;
			}
			int c3 = toInt[s.charAt(i + 3)];
			buffer[index++] = (byte) (((c2 << 6) | c3) & mask);
		}
		return buffer;
	}

}