base64.java

j2me游戏开发 源代码

import java.io.*;

public class Base64 {
    protected static final char[] alphabet = {
	'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', // 0 to 7
	'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', // 8 to 15
	'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', // 16 to 23
	'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', // 24 to 31
	'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', // 32 to 39
	'o', 'p', 'q', 'r', 's', 't', 'u', 'v', // 40 to 47
	'w', 'x', 'y', 'z', '0', '1', '2', '3', // 48 to 55
	'4', '5', '6', '7', '8', '9', '+', '/'  // 56 to 63
    };

    protected static final int[] decodeTable = {
	-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 0 to 9
	-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 10 to 19
	-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 20 to 29
	-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 30 to 39
	-1, -1, -1, 62, -1, -1, -1, 63, 52, 53, // 40 to 49
	54, 55, 56, 57, 58, 59, 60, 61, -1, -1, // 50 to 59
	-1, -1, -1, -1, -1,  0,  1,  2,  3,  4, // 60 to 69
	 5,  6,  7,  8,  9, 10, 11, 12, 13, 14, // 70 to 79
	15, 16, 17, 18, 19, 20, 21, 22, 23, 24, // 80 to 89
	25, -1, -1, -1, -1, -1, -1, 26, 27, 28, // 90 to 99
	29, 30, 31, 32, 33, 34, 35, 36, 37, 38, // 100 to 109
	39, 40, 41, 42, 43, 44, 45, 46, 47, 48, // 110 to 119
	49, 50, 51                              // 120 to 122
    };
    
    public static String encodeToString(String s) {
      char[] encoded = encode(s);	
      StringBuffer encodedSB = new StringBuffer();
      for (int i=0; i<encoded.length; i++) {
      	encodedSB.append(encoded[i]);
      }
      return encodedSB.toString();
    }

    public static char[] encode(String s) {
	return encode(s.getBytes());
    }

    public static char[] encode(byte[] bytes) {
	int sixbit;

	char[] output = new char[((bytes.length - 1) / 3 + 1) * 4];

	int outIndex = 0;
	int i = 0;

	while ((i + 3) <= bytes.length) {
	    sixbit = (bytes[i] & 0xFC) >> 2;
	    output[outIndex++] = alphabet[sixbit];
	    sixbit = ((bytes[i] & 0x3) << 4) + ((bytes[i + 1] & 0xF0) >> 4);
	    output[outIndex++] = alphabet[sixbit];
	    sixbit = ((bytes[i + 1] & 0xF) << 2) + ((bytes[i + 2] & 0xC0) >> 6);
	    output[outIndex++] = alphabet[sixbit];
	    sixbit = bytes[i + 2] & 0x3F;
	    output[outIndex++] = alphabet[sixbit];
	    i += 3;
	}

	if (bytes.length - i == 2) {
	    sixbit = (bytes[i] & 0xFC) >> 2;
	    output[outIndex++] = alphabet[sixbit];
	    sixbit = ((bytes[i] & 0x3) << 4) + ((bytes[i + 1] & 0xF0) >> 4);
	    output[outIndex++] = alphabet[sixbit];
	    sixbit = (bytes[i + 1] & 0xF) << 2;
	    output[outIndex++] = alphabet[sixbit];
	    output[outIndex++] = '=';
	} else if (bytes.length - i == 1) {
	    sixbit = (bytes[i] & 0xFC) >> 2;
	    output[outIndex++] = alphabet[sixbit];
	    sixbit = (bytes[i] & 0x3) << 4;
	    output[outIndex++] = alphabet[sixbit];
	    output[outIndex++] = '=';
	    output[outIndex++] = '=';
	}
	return output;
    }
    
    public static String decodeToString(String encoded) {
       byte[] decoded = decode(encoded);
       StringBuffer decodedSB = new StringBuffer();
       for (int i=0; i< decoded.length; i++) {        
        decodedSB.append( (char)decoded[i]);
       }       
       return decodedSB.toString();	
    }

    public static byte[] decode(String encoded) {
	byte[] decoded = null;
	int decodedLength = (encoded.length() / 4 * 3);
	int invalid = 0;

	if (encoded.length() % 4 != 0) {
	    System.err.println("It's not BASE64 encoded string.");
	    return null;
	}
	if (encoded.charAt(encoded.length() - 2) == '=') {
	    invalid = 2;
	} else if (encoded.charAt(encoded.length() - 1) == '=') {
	    invalid = 1;
	}
	decodedLength -= invalid;
	decoded = new byte[decodedLength];

	int i = 0, di = 0;
	int sixbit0, sixbit1, sixbit2, sixbit3;

	for (; i < encoded.length() - 4; i += 4) {
	    sixbit0 = decodeTable[encoded.charAt(i)];
	    sixbit1 = decodeTable[encoded.charAt(i + 1)];
	    sixbit2 = decodeTable[encoded.charAt(i + 2)];
	    sixbit3 = decodeTable[encoded.charAt(i + 3)];

	    decoded[di++] = (byte) ((sixbit0 << 2) + ((sixbit1 & 0x30) >> 4));
	    decoded[di++] = (byte) (((sixbit1 & 0xF) << 4) + ((sixbit2 & 0x3C) >> 2));
	    decoded[di++] = (byte) (((sixbit2 & 0x3) << 6) + sixbit3);
	}


	switch (invalid) {
	case 0 :
	    sixbit0 = decodeTable[encoded.charAt(i)];
	    sixbit1 = decodeTable[encoded.charAt(i + 1)];
	    sixbit2 = decodeTable[encoded.charAt(i + 2)];
	    sixbit3 = decodeTable[encoded.charAt(i + 3)];

	    decoded[di++] = (byte) ((sixbit0 << 2) + ((sixbit1 & 0x30) >> 4));
	    decoded[di++] = (byte) (((sixbit1 & 0xF) << 4) + ((sixbit2 & 0x3C) >> 2));
	    decoded[di++] = (byte) (((sixbit2 & 0x3) << 6) + sixbit3);
	    break;

	case 1 :
	    sixbit0 = decodeTable[encoded.charAt(i)];
	    sixbit1 = decodeTable[encoded.charAt(i + 1)];
	    sixbit2 = decodeTable[encoded.charAt(i + 2)];

	    decoded[di++] = (byte) ((sixbit0 << 2) + ((sixbit1 & 0x30) >> 4));
	    decoded[di++] = (byte) (((sixbit1 & 0xF) << 4) + ((sixbit2 & 0x3C) >> 2));
	    break;

	case 2 :
	    sixbit0 = decodeTable[encoded.charAt(i)];
	    sixbit1 = decodeTable[encoded.charAt(i + 1)];

	    decoded[di++] = (byte) ((sixbit0 << 2) + ((sixbit1 & 0x30) >> 4));
	    break;
	}

	return decoded;
    }

    static boolean bytesEquals(byte[] b1, byte[] b2) {
	if (b1.length != b2.length) {
	    return false;
	}

	for (int i = b1.length - 1; i >= 0; i--) {
	    if (b1[i] != b2[i]) {
		return false;
	    }
	}
	return true;
    }
}