字节数组与字符串的编码与解码

import java.io.ByteArrayOutputStream;

public class Base64Utils {
    private static final 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 Base64Utils() {
    }
    
    /**
     * 将字节数组编码为字符串
     * 
     * @param data
     */
    public static String encode(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();
    }
    
    /**
     * 将base64字符串解码为字节数组
     * 
     * @param str
     */
    public static byte[] decode(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((int) ((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((int) (((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((int) (((b3 & 0x03) << 6) | b4));
        }
        return buf.toByteArray();
    }
}