Java Byte Array Decode decode(final byte[] source, final int off, final int len)

Description

Very low-level access to decoding ASCII characters in the form of a byte array.

License

Apache License

Parameter

Parameter	Description
source	The org.codelogger.utils.Base64Util encoded data
off	The offset of where to begin decoding
len	The length of characters to decode

Return

decoded data

Declaration

public static byte[] decode(final byte[] source, final int off, final int len) 

Method Source Code

//package com.java2s;
//License from project: Apache License 

public class Main {
    /**//  www.  j a v a2 s  .  c o  m
     * The equals sign (=) as a byte.
     */
    private final static byte EQUALS_SIGN = (byte) '=';
    /**
     * Preferred encoding.
     */
    private final static String PREFERRED_ENCODING = "UTF-8";
    /**
     * Translates a org.codelogger.utils.Base64Util value to either its
     * 6-bit reconstruction value or a negative number indicating some other
     * meaning.
     */
    private final static byte[] DECODABET = { -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal
            // 0
            // -
            // 8
            -5, -5, // Whitespace: Tab and Linefeed
            -9, -9, // Decimal 11 - 12
            -5, // Whitespace: Carriage Return
            -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 14 -
            // 26
            -9, -9, -9, -9, -9, // Decimal 27 - 31
            -5, // Whitespace: Space
            -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 33 - 42
            62, // Plus sign at decimal 43
            -9, -9, -9, // Decimal 44 - 46
            63, // Slash at decimal 47
            52, 53, 54, 55, 56, 57, 58, 59, 60, 61, // Numbers zero through nine
            -9, -9, -9, // Decimal 58 - 60
            -1, // Equals sign at decimal 61
            -9, -9, -9, // Decimal 62 - 64
            0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, // Letters 'A' through
            // 'N'
            14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, // Letters 'O'
            // through 'Z'
            -9, -9, -9, -9, -9, -9, // Decimal 91 - 96
            26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, // Letters 'a'
            // through 'm'
            39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, // Letters 'n'
            // through 'z'
            -9, -9, -9, -9 // Decimal 123 - 126
            /*
             * ,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9, // Decimal 127 - 139
             * -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9, // Decimal 140 - 152
             * -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9, // Decimal 153 - 165
             * -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9, // Decimal 166 - 178
             * -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9, // Decimal 179 - 191
             * -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9, // Decimal 192 - 204
             * -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9, // Decimal 205 - 217
             * -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9, // Decimal 218 - 230
             * -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9, // Decimal 231 - 243
             * -9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9 // Decimal 244 - 255
             */
    };
    private final static byte WHITE_SPACE_ENC = -5;
    private final static byte EQUALS_SIGN_ENC = -1;

    /**
     * Very low-level access to decoding ASCII characters in the form of a byte
     * array. Does not support automatically gunzipping or any other "fancy"
     * features.
     * 
     * @param source
     *            The org.codelogger.utils.Base64Util encoded data
     * @param off
     *            The offset of where to begin decoding
     * @param len
     *            The length of characters to decode
     * @return decoded data
     * @since 1.3
     */
    public static byte[] decode(final byte[] source, final int off, final int len) {

        int len34 = len * 3 / 4;
        byte[] outBuff = new byte[len34]; // Upper limit on size of output
        int outBuffPosn = 0;

        byte[] b4 = new byte[4];
        int b4Posn = 0;
        int i = 0;
        byte sbiCrop = 0;
        byte sbiDecode = 0;
        for (i = off; i < off + len; i++) {
            sbiCrop = (byte) (source[i] & 0x7f); // Only the low seven bits
            sbiDecode = DECODABET[sbiCrop];

            if (sbiDecode >= WHITE_SPACE_ENC) // White space, Equals sign or
                                              // better
            {
                if (sbiDecode >= EQUALS_SIGN_ENC) {
                    b4[b4Posn++] = sbiCrop;
                    if (b4Posn > 3) {
                        outBuffPosn += decode4to3(b4, 0, outBuff, outBuffPosn);
                        b4Posn = 0;

                        // If that was the equals sign, break out of 'for' loop
                        if (sbiCrop == EQUALS_SIGN)
                            break;
                    } // end if: quartet built

                } // end if: equals sign or better

            } // end if: white space, equals sign or better
            else {
                System.err.println("Bad org.codelogger.utils.Base64Util input character at " + i + ": " + source[i]
                        + "(decimal)");
                return null;
            } // end else:
        } // each input character

        byte[] out = new byte[outBuffPosn];
        System.arraycopy(outBuff, 0, out, 0, outBuffPosn);
        return out;
    }

    /**
     * Decodes data from org.codelogger.utils.Base64Util notation,
     * automatically detecting gzip-compressed data and decompressing it.
     * 
     * @param s
     *            the string to decode
     * @return the decoded data
     * @since 1.4
     */
    public static byte[] decode(final String s) {

        byte[] bytes;
        try {
            bytes = s.getBytes(PREFERRED_ENCODING);
        } // end try
        catch (java.io.UnsupportedEncodingException uee) {
            bytes = s.getBytes();
        } // end catch
          // </change>

        // Decode
        bytes = decode(bytes, 0, bytes.length);

        // Check to see if it's gzip-compressed
        // GZIP Magic Two-Byte Number: 0x8b1f (35615)
        if (bytes != null && bytes.length >= 4) {

            int head = (bytes[0] & 0xff) | ((bytes[1] << 8) & 0xff00);
            if (java.util.zip.GZIPInputStream.GZIP_MAGIC == head) {
                java.io.ByteArrayInputStream bais = null;
                java.util.zip.GZIPInputStream gzis = null;
                java.io.ByteArrayOutputStream baos = null;
                byte[] buffer = new byte[2048];
                int length = 0;

                try {
                    baos = new java.io.ByteArrayOutputStream();
                    bais = new java.io.ByteArrayInputStream(bytes);
                    gzis = new java.util.zip.GZIPInputStream(bais);

                    while ((length = gzis.read(buffer)) >= 0) {
                        baos.write(buffer, 0, length);
                    } // end while: reading input

                    // No error? Get new bytes.
                    bytes = baos.toByteArray();

                } // end try
                catch (java.io.IOException e) {
                    // Just return originally-decoded bytes
                } // end catch
                finally {
                    try {
                        baos.close();
                    } catch (Exception e) {
                    }
                    try {
                        gzis.close();
                    } catch (Exception e) {
                    }
                    try {
                        bais.close();
                    } catch (Exception e) {
                    }
                } // end finally

            } // end if: gzipped
        } // end if: bytes.length >= 2

        return bytes;
    }

    /**
     * Decodes four bytes from array <var>source</var> and writes the resulting
     * bytes (up to three of them) to <var>destination</var>. The source and
     * destination arrays can be manipulated anywhere along their length by
     * specifying <var>srcOffset</var> and <var>destOffset</var>. This method
     * does not check to make sure your arrays are large enough to accomodate
     * <var>srcOffset</var> + 4 for the <var>source</var> array or
     * <var>destOffset</var> + 3 for the <var>destination</var> array. This
     * method returns the actual number of bytes that were converted from the
     * org.codelogger.utils.Base64Util encoding.
     * 
     * @param source
     *            the array to convert
     * @param srcOffset
     *            the index where conversion begins
     * @param destination
     *            the array to hold the conversion
     * @param destOffset
     *            the index where output will be put
     * @return the number of decoded bytes converted
     * @since 1.3
     */
    private static int decode4to3(final byte[] source, final int srcOffset, final byte[] destination,
            final int destOffset) {

        // Example: Dk==
        if (source[srcOffset + 2] == EQUALS_SIGN) {
            // Two ways to do the same thing. Don't know which way I like best.
            // int outBuff = ( ( DECODABET[ source[ srcOffset ] ] << 24 ) >>> 6
            // )
            // | ( ( DECODABET[ source[ srcOffset + 1] ] << 24 ) >>> 12 );
            int outBuff = ((DECODABET[source[srcOffset]] & 0xFF) << 18)
                    | ((DECODABET[source[srcOffset + 1]] & 0xFF) << 12);

            destination[destOffset] = (byte) (outBuff >>> 16);
            return 1;
        }

        // Example: DkL=
        else if (source[srcOffset + 3] == EQUALS_SIGN) {
            // Two ways to do the same thing. Don't know which way I like best.
            // int outBuff = ( ( DECODABET[ source[ srcOffset ] ] << 24 ) >>> 6
            // )
            // | ( ( DECODABET[ source[ srcOffset + 1 ] ] << 24 ) >>> 12 )
            // | ( ( DECODABET[ source[ srcOffset + 2 ] ] << 24 ) >>> 18 );
            int outBuff = ((DECODABET[source[srcOffset]] & 0xFF) << 18)
                    | ((DECODABET[source[srcOffset + 1]] & 0xFF) << 12)
                    | ((DECODABET[source[srcOffset + 2]] & 0xFF) << 6);

            destination[destOffset] = (byte) (outBuff >>> 16);
            destination[destOffset + 1] = (byte) (outBuff >>> 8);
            return 2;
        }

        // Example: DkLE
        else {
            try {
                // Two ways to do the same thing. Don't know which way I like
                // best.
                // int outBuff = ( ( DECODABET[ source[ srcOffset ] ] << 24 )
                // >>> 6 )
                // | ( ( DECODABET[ source[ srcOffset + 1 ] ] << 24 ) >>> 12 )
                // | ( ( DECODABET[ source[ srcOffset + 2 ] ] << 24 ) >>> 18 )
                // | ( ( DECODABET[ source[ srcOffset + 3 ] ] << 24 ) >>> 24 );
                int outBuff = ((DECODABET[source[srcOffset]] & 0xFF) << 18)
                        | ((DECODABET[source[srcOffset + 1]] & 0xFF) << 12)
                        | ((DECODABET[source[srcOffset + 2]] & 0xFF) << 6)
                        | ((DECODABET[source[srcOffset + 3]] & 0xFF));

                destination[destOffset] = (byte) (outBuff >> 16);
                destination[destOffset + 1] = (byte) (outBuff >> 8);
                destination[destOffset + 2] = (byte) (outBuff);

                return 3;
            } catch (Exception e) {
                System.out.println("" + source[srcOffset] + ": " + (DECODABET[source[srcOffset]]));
                System.out.println("" + source[srcOffset + 1] + ": " + (DECODABET[source[srcOffset + 1]]));
                System.out.println("" + source[srcOffset + 2] + ": " + (DECODABET[source[srcOffset + 2]]));
                System.out.println("" + source[srcOffset + 3] + ": " + (DECODABET[source[srcOffset + 3]]));
                return -1;
            } // e nd catch
        }
    }
}

Related

1. decode(byte[] msgToDecode)
2. decode(byte[] source)
3. decode(byte[] source, int off, int len)
4. decode(byte[] src, String charset)
5. decode(Byte[] wrap)
6. decode(String encoding, byte[] bytes)
7. decode(String encoding, byte[] data)
8. decodeBytes(byte[] data, String encoding)
9. decodeObject(byte[] bytes)