create your own Base64 decode - Android File Input Output

Android examples for File Input Output:Base64

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Description

create your own Base64 decode

Demo Code


//package com.java2s;
import java.io.UnsupportedEncodingException;

public class Main {
    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 };

    public static byte[] decode(String str) {
        try {/* ww w  . j av a 2s .  co m*/
            return decodePrivate(str);
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        }
        return new byte[] {};
    }

    private static byte[] decodePrivate(String str)
            throws UnsupportedEncodingException {
        StringBuffer sb = new StringBuffer();
        byte[] data = null;
        data = str.getBytes("US-ASCII");
        int len = data.length;
        int i = 0;
        int b1, b2, b3, b4;
        while (i < len) {

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

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

            do {
                b3 = data[i++];
                if (b3 == 61)
                    return sb.toString().getBytes("iso8859-1");
                b3 = base64DecodeChars[b3];
            } while (i < len && b3 == -1);
            if (b3 == -1)
                break;
            sb.append((char) (((b2 & 0x0f) << 4) | ((b3 & 0x3c) >>> 2)));

            do {
                b4 = data[i++];
                if (b4 == 61)
                    return sb.toString().getBytes("iso8859-1");
                b4 = base64DecodeChars[b4];
            } while (i < len && b4 == -1);
            if (b4 == -1)
                break;
            sb.append((char) (((b3 & 0x03) << 6) | b4));
        }
        return sb.toString().getBytes("iso8859-1");
    }
}

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