安卓 图片base64编码

Question

网上看了几种办法，无论是安卓自带的util包下的base64还是sun.misc.Encoder包下的base64，
转码之后都转不回图片，卡了两天了，有人能帮忙么？

Answer 1

要自定义Base64
package com.lixue.app.library.util;

import java.io.IOException;
import java.nio.charset.Charset;

public class Base64 {
/** prevents anyone from instantiating this class */
private Base64() {
}

/**
 * This character array provides the alphabet map from RFC1521.
 */
private final static byte ALPHABET[] = {
// 0 1 2 3 4 5 6 7
        'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H',// 0
        'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',// 1
        'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X',// 2
        'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',// 3
        'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n',// 4
        'o', 'p', 'q', 'r', 's', 't', 'u', 'v',// 5
        'w', 'x', 'y', 'z', '0', '1', '2', '3',// 6
        '4', '5', '6', '7', '8', '9', '+', '/' // 7
};

/**
 * Decodes a 7 bit Base64 character into its binary value.
 */
private static int valueDecoding[] = new int[128];

/**
 * initializes the value decoding array from the character map
 */
static {
    for (int i = 0; i < valueDecoding.length; i++) {
        valueDecoding[i] = -1;
    }

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

/**
 * Converts a byte array into a Base64 encoded string.
 * 
 * @param data
 *            bytes to encode
 * @param offset
 *            which byte to start at
 * @param length
 *            how many bytes to encode; padding will be added if needed
 * @return base64 encoding of data; 4 chars for every 3 bytes
 */
public static String encode(byte[] data, int offset, int length) {
    int i;
    int encodedLen;
    byte[] encoded;

    // 4 chars for 3 bytes, run input up to a multiple of 3
    encodedLen = (length + 2) / 3 * 4;
    encoded = new byte[encodedLen];

    for (i = 0, encodedLen = 0; encodedLen < encoded.length; i += 3, encodedLen += 4) {
        encodeQuantum(data, offset + i, length - i, encoded, encodedLen);
    }

    return new String(encoded, Charset.forName("UTF-8"));
}

/**
 * Encodes 1, 2, or 3 bytes of data as 4 Base64 chars.
 * 
 * @param in
 *            buffer of bytes to encode
 * @param inOffset
 *            where the first byte to encode is
 * @param len
 *            how many bytes to encode
 * @param out
 *            buffer to put the output in
 * @param outOffset
 *            where in the output buffer to put the chars
 */
private static void encodeQuantum(byte in[], int inOffset, int len,
                                  byte out[], int outOffset) {
    byte a = 0, b = 0, c = 0;

    a = in[inOffset];
    out[outOffset] = ALPHABET[(a >>> 2) & 0x3F];

    if (len > 2) {
        b = in[inOffset + 1];
        c = in[inOffset + 2];
        out[outOffset + 1] = ALPHABET[((a << 4) & 0x30) + ((b >>> 4) & 0xf)];
        out[outOffset + 2] = ALPHABET[((b << 2) & 0x3c) + ((c >>> 6) & 0x3)];
        out[outOffset + 3] = ALPHABET[c & 0x3F];
    } else if (len > 1) {
        b = in[inOffset + 1];
        out[outOffset + 1] = ALPHABET[((a << 4) & 0x30) + ((b >>> 4) & 0xf)];
        out[outOffset + 2] = ALPHABET[((b << 2) & 0x3c) + ((c >>> 6) & 0x3)];
        out[outOffset + 3] = '=';
    } else {
        out[outOffset + 1] = ALPHABET[((a << 4) & 0x30) + ((b >>> 4) & 0xf)];
        out[outOffset + 2] = '=';
        out[outOffset + 3] = '=';
    }
}

/**
 * Converts a Base64 encoded string to a byte array.
 * 
 * @param encoded
 *            Base64 encoded data
 * @return decode binary data; 3 bytes for every 4 chars - minus padding
 * @exception IOException
 *                is thrown, if an I/O error occurs reading the data
 */
public static byte[] decode(String encoded) throws IOException {
    return decode(encoded, 0, encoded.length());
}

/**
 * Converts an embedded Base64 encoded string to a byte array.
 * 
 * @param encoded
 *            a String with Base64 data embedded in it
 * @param offset
 *            which char of the String to start at
 * @param length
 *            how many chars to decode; must be a multiple of 4
 * @return decode binary data; 3 bytes for every 4 chars - minus padding
 * @exception IOException
 *                is thrown, if an I/O error occurs reading the data
 */
public static byte[] decode(String encoded, int offset, int length)
        throws IOException {
    int i;
    int decodedLen;
    byte[] decoded;

    // the input must be a multiple of 4
    if (length % 4 != 0) {
        throw new IOException("Base64 string length is not multiple of 4");
    }

    // 4 chars for 3 bytes, but there may have been pad bytes
    decodedLen = length / 4 * 3;
    if (encoded.charAt(offset + length - 1) == '=') {
        decodedLen--;
        if (encoded.charAt(offset + length - 2) == '=') {
            decodedLen--;
        }
    }

    decoded = new byte[decodedLen];
    for (i = 0, decodedLen = 0; i < length; i += 4, decodedLen += 3) {
        decodeQuantum(encoded.charAt(offset + i), encoded.charAt(offset + i
                + 1), encoded.charAt(offset + i + 2), encoded.charAt(offset
                + i + 3), decoded, decodedLen);
    }

    return decoded;
}

/**
 * Decode 4 Base64 chars as 1, 2, or 3 bytes of data.
 * 
 * @param in1
 *            first char of quantum to decode
 * @param in2
 *            second char of quantum to decode
 * @param in3
 *            third char of quantum to decode
 * @param in4
 *            forth char of quantum to decode
 * @param out
 *            buffer to put the output in
 * @param outOffset
 *            where in the output buffer to put the bytes
 */
private static void decodeQuantum(char in1, char in2, char in3, char in4,
        byte[] out, int outOffset) throws IOException {
    int a = 0, b = 0, c = 0, d = 0;
    int pad = 0;

    a = valueDecoding[in1 & 127];
    b = valueDecoding[in2 & 127];

    if (in4 == '=') {
        pad++;
        if (in3 == '=') {
            pad++;
        } else {
            c = valueDecoding[in3 & 127];
        }
    } else {
        c = valueDecoding[in3 & 127];
        d = valueDecoding[in4 & 127];
    }

    if (a < 0 || b < 0 || c < 0 || d < 0) {
        throw new IOException("Invalid character in Base64 string");
    }

    // the first byte is the 6 bits of a and 2 bits of b
    out[outOffset] = (byte) (((a << 2) & 0xfc) | ((b >>> 4) & 3));

    if (pad < 2) {
        // the second byte is 4 bits of b and 4 bits of c
        out[outOffset + 1] = (byte) (((b << 4) & 0xf0) | ((c >>> 2) & 0xf));

        if (pad < 1) {
            // the third byte is 2 bits of c and 4 bits of d
            out[outOffset + 2] = (byte) (((c << 6) & 0xc0) | (d & 0x3f));
        }
    }
}

}