/**
 * Base64转换工具
 * @author:Nemo 2017年04月25日
 */
public class Base64Util {

        private static final char intToBase64[] = {'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 final byte base64ToInt[] = {-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 };

        /**
         * byte数组转换成BASE64字符串
         *
         * @param data byte数组
         * @return <b>String</b> BASE64字符串<b><br/>null</b> 转换失败
         */
        public static String byteArrayToBase64(byte[] data) {
            if(data==null || data.length==0){
                return null;
            }
            int len = data.length;
            int groups = len/3;
            int nogroups = len-3*groups;
            int resultLen = (len+2)/3*4;
            StringBuffer result = new StringBuffer(resultLen);
            int cursor = 0;
            for(int i=0;i<groups;i++){
                int byte0 = data[cursor++]&0xff;
                int byte1 = data[cursor++]&0xff;
                int byte2 = data[cursor++]&0xff;
                result.append(intToBase64[byte0>>2]);
                result.append(intToBase64[(byte0<<4)&0x3f|(byte1>>4)]);
                result.append(intToBase64[(byte1<<2)&0x3f|(byte2>>6)]);
                result.append(intToBase64[byte2&0x3f]);
            }
            if(nogroups!=0){
                int byte0 = data[cursor++]&0xff;
                result.append(intToBase64[byte0>>2]);
                if(nogroups==1){
                    result.append(intToBase64[(byte0<<4)&0x3f]);
                    result.append("==");
                }else{
                    int byte1 = data[cursor++]&0xff;
                    result.append(intToBase64[(byte0<<4)&0x3f|(byte1>>4)]);
                    result.append(intToBase64[(byte1<<2)&0x3f]);
                    result.append('=');
                }
            }
            return result.toString();
        }

        /**
         * BASE64字符串转换成byte数组
         *
         * @param data BASE64字符串
         * @return <b>String</b> byte数组<b><br/>null</b> 转换失败
         */
        public static byte[] base64ToByteArray(String data) {
            if(data==null || "".equals(data.trim())){
                return null;
            }
            int len = data.length();
            int groups = len/4;
            if(groups*4!=len){
                return null;
            }
            int nogroups = 0;
            int fullGroups = groups;
            if(len!=0){
                if(data.charAt(len-1)=='='){
                    nogroups++;
                    fullGroups--;
                }
                if(data.charAt(len-2)=='='){
                    nogroups++;
                }
            }
            byte[] result = new byte[groups*3-nogroups];
            int inCursor = 0;
            int outCursor = 0;
            try {
                for(int i=0;i<fullGroups;i++){
                    int ch0 = base64toInt(data.charAt(inCursor++));
                    int ch1 = base64toInt(data.charAt(inCursor++));
                    int ch2 = base64toInt(data.charAt(inCursor++));
                    int ch3 = base64toInt(data.charAt(inCursor++));
                    result[outCursor++] = (byte) ((ch0<<2)|(ch1>>4));
                    result[outCursor++] = (byte) ((ch1<<4)|(ch2>>2));
                    result[outCursor++] = (byte) ((ch2<<6)|ch3);
                }
                if(nogroups!=0){
                    int ch0 = base64toInt(data.charAt(inCursor++));
                    int ch1 = base64toInt(data.charAt(inCursor++));
                    result[outCursor++] = (byte) ((ch0<<2)|(ch1>>4));
                    if(nogroups==1){
                        int ch2 = base64toInt(data.charAt(inCursor++));
                        result[outCursor++] = (byte) ((ch1<<4)|(ch2>>2));
                    }
                }
            } catch (Exception e) {
                return null;
            }
            return result;
        }

        private static int base64toInt(char c) {
            int result = base64ToInt[c];
            if(result<0){
                throw new RuntimeException();
            }
            return result;
        }

}