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/*
+--------------------------------------------------------------------------
|   mtons [#RELEASE_VERSION#]
|   ========================================
|   Copyright (c) 2014, 2015 mtons. All Rights Reserved
|   http://www.mtons.com
|
+---------------------------------------------------------------------------
*/
package mtons.security;

import java.io.ByteArrayOutputStream;

/**
 * Base64加密解密算法
 * 
 * @author langhsu
 *
 */
public class Base64 {
	private static char[] base64EncodeChars = new char[] { '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', '+', '/' };
	private static byte[] base64DecodeChars = new byte[] { -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, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
			-1, 62, -1, -1, -1, 63, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1, -1, 0, 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, -1, -1, -1, -1, -1, -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 Base64() {
	}

	/**
	 * Base64编码
	 * 
	 * @param data byte[] 明文
	 * @return string 密文
	 */
	public static String encodeBase64(byte[] data) {
		StringBuffer sb = new StringBuffer();
		int len = data.length;
		int i = 0;
		int b1, b2, b3;

		while (i < len) {
			b1 = data[i++] & 0xff;
			if (i == len) {
				sb.append(base64EncodeChars[b1 >>> 2]);
				sb.append(base64EncodeChars[(b1 & 0x3) << 4]);
				sb.append("==");
				break;
			}
			b2 = data[i++] & 0xff;
			if (i == len) {
				sb.append(base64EncodeChars[b1 >>> 2]);
				sb.append(base64EncodeChars[((b1 & 0x03) << 4) | ((b2 & 0xf0) >>> 4)]);
				sb.append(base64EncodeChars[(b2 & 0x0f) << 2]);
				sb.append("=");
				break;
			}
			b3 = data[i++] & 0xff;
			sb.append(base64EncodeChars[b1 >>> 2]);
			sb.append(base64EncodeChars[((b1 & 0x03) << 4) | ((b2 & 0xf0) >>> 4)]);
			sb.append(base64EncodeChars[((b2 & 0x0f) << 2) | ((b3 & 0xc0) >>> 6)]);
			sb.append(base64EncodeChars[b3 & 0x3f]);
		}
		return sb.toString();
	}

	/**
	 * Base64解码
	 * 
	 * @param str 密文
	 * @return byte[] 明文
	 */
	public static byte[] decodeBase64(String str) {
		byte[] data = str.getBytes();
		int len = data.length;
		ByteArrayOutputStream buf = new ByteArrayOutputStream(len);
		int i = 0;
		int b1, b2, b3, b4;

		while (i < len) {

			/* b1 */
			do {
				b1 = base64DecodeChars[data[i++]];
			} while (i < len && b1 == -1);
			if (b1 == -1) {
				break;
			}

			/* b2 */
			do {
				b2 = base64DecodeChars[data[i++]];
			} while (i < len && b2 == -1);
			if (b2 == -1) {
				break;
			}
			buf.write(((b1 << 2) | ((b2 & 0x30) >>> 4)));

			/* b3 */
			do {
				b3 = data[i++];
				if (b3 == 61) {
					return buf.toByteArray();
				}
				b3 = base64DecodeChars[b3];
			} while (i < len && b3 == -1);
			if (b3 == -1) {
				break;
			}
			buf.write((((b2 & 0x0f) << 4) | ((b3 & 0x3c) >>> 2)));

			/* b4 */
			do {
				b4 = data[i++];
				if (b4 == 61) {
					return buf.toByteArray();
				}
				b4 = base64DecodeChars[b4];
			} while (i < len && b4 == -1);
			if (b4 == -1) {
				break;
			}
			buf.write((((b3 & 0x03) << 6) | b4));
		}
		return buf.toByteArray();
	}
	
	/**
	 * 使用Base64加密算法加密字符串
	 * 
	 * @param plain 明文
	 * @return 密文
	 */
	public static String encode(String plain) {
		return encodeBase64(plain.getBytes());
	}

	/**
	 * 使用Base64解密
	 * 
	 * @param base64Encoded 密文
	 * @return 明文
	 */
	public static String decode(String base64Encoded) {
		return new String(decodeBase64(base64Encoded));
	}
}