base64.java

java写的base64加解码算法

//*********************************************************************
//* Base64 - a simple base64 encoder and decoder.
//*
//*     Copyright (c) 1999, Bob Withers - [e-mail]
//*
//* This code may be freely used for any purpose, either personal
//* or commercial, provided the authors copyright notice remains
//* intact.
//*********************************************************************


public class Base64
{
    public static String encode(String data)
    {
        return(getString(encode(getBinaryBytes(data))));
    }

    public static byte[] encode(byte[] data)
    {
        int c;
        int len = data.length;
        StringBuffer ret = new StringBuffer(((len / 3) + 1) * 4);
        for (int i = 0; i < len; ++i)
        {
            c = (data[i] >> 2) & 0x3f;
            ret.append(cvt.charAt(c));
            c = (data[i] << 4) & 0x3f;
            if (++i < len)
                c |= (data[i] >> 4) & 0x0f;

            ret.append(cvt.charAt(c));
            if (i < len)
            {
                c = (data[i] << 2) & 0x3f;
                if (++i < len)
                    c |= (data[i] >> 6) & 0x03;

                ret.append(cvt.charAt(c));
            }
            else
            {
                ++i;
                ret.append((char) fillchar);
            }

            if (i < len)
            {
                c = data[i] & 0x3f;
                ret.append(cvt.charAt(c));
            }
            else
            {
                ret.append((char) fillchar);
            }
        }

        return(getBinaryBytes(ret.toString()));
    }

    public static String decode(String data)
    {
        return(getString(decode(getBinaryBytes(data))));
    }

    public static byte[] decode(byte[] data)
    {
        int c;
        int c1;
        int len = data.length;
        StringBuffer ret = new StringBuffer((len * 3) / 4);
        for (int i = 0; i < len; ++i)
        {
            c = cvt.indexOf(data[i]);
            ++i;
            c1 = cvt.indexOf(data[i]);
            c = ((c << 2) | ((c1 >> 4) & 0x3));
            ret.append((char) c);
            if (++i < len)
            {
                c = data[i];
                if (fillchar == c)
                    break;

                c = cvt.indexOf((char) c);
                c1 = ((c1 << 4) & 0xf0) | ((c >> 2) & 0xf);
                ret.append((char) c1);
            }

            if (++i < len)
            {
                c1 = data[i];
                if (fillchar == c1)
                    break;

                c1 = cvt.indexOf((char) c1);
                c = ((c << 6) & 0xc0) | c1;
                ret.append((char) c);
            }
        }

        return(getBinaryBytes(ret.toString()));
    }

    private static String getString(byte[] arr)
    {
        StringBuffer buf = new StringBuffer();
        for (int i = 0; i < arr.length; ++i)
            buf.append((char) arr[i]);

        return(buf.toString());
    }

    private static byte[] getBinaryBytes(String str)
    {
        byte[] b = new byte[str.length()];
        for (int i = 0; i < b.length; ++i)
            b[i] = (byte) str.charAt(i);

        return(b);
    }

    private static final int    fillchar = '=';

                                    // 00000000001111111111222222
                                    // 01234567890123456789012345
    private static final String cvt = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"

                                    // 22223333333333444444444455
                                    // 67890123456789012345678901
                                    + "abcdefghijklmnopqrstuvwxyz"

                                    // 555555556666
                                    // 234567890123
                                    + "0123456789+/";

    public static void main(String[] args)
    {
        String str;
        if (args.length > 0)
            str = args[0];
        else
            str = "Now is the time for all good men";

        System.out.println("Encoding string [" + str + "]");
        str = encode(str);
        System.out.println("Encoded string  [" + str + "]");
        str = decode(str);
        System.out.println("Decoded string  [" + str + "]");
        System.out.println();
        byte[] b = getBinaryBytes(str);
        System.out.println("Encoding bytes  [" + getString(b) + "]");
        b = encode(b);
        System.out.println("Encoded bytes   [" + getString(b) + "]");
        b = decode(b);
        System.out.println("Decoded bytes   [" + getString(b) + "]");
    }
}