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Java example source code file (BASE64Decoder.java)

This example Java source code file (BASE64Decoder.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

a\'\,\'b\'\,\'c\'\,\'d\'\,\'e\'\,\'f\'\,\'g\'\,\'h, base64decoder, ceformatexception, cestreamexhausted, characterdecoder, i\'\,\'j\'\,\'k\'\,\'l\'\,\'m\'\,\'n\'\,\'o\'\,\'p, not, outputstream, q\'\,\'r\'\,\'s\'\,\'t\'\,\'u\'\,\'v\'\,\'w\'\,\'x, suppresswarnings, y','z','a','b','c','d','e','f

The BASE64Decoder.java Java example source code

/*
 * Copyright (c) 1995, 2011, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */
package sun.misc;

import java.io.OutputStream;
import java.io.PushbackInputStream;
import java.io.PrintStream;

/**
 * This class implements a BASE64 Character decoder as specified in RFC1521.
 *
 * This RFC is part of the MIME specification which is published by the
 * Internet Engineering Task Force (IETF). Unlike some other encoding
 * schemes there is nothing in this encoding that tells the decoder
 * where a buffer starts or stops, so to use it you will need to isolate
 * your encoded data into a single chunk and then feed them this decoder.
 * The simplest way to do that is to read all of the encoded data into a
 * string and then use:
 * <pre>
 *      byte    mydata[];
 *      BASE64Decoder base64 = new BASE64Decoder();
 *
 *      mydata = base64.decodeBuffer(bufferString);
 * </pre>
 * This will decode the String in <i>bufferString and give you an array
 * of bytes in the array <i>myData.
 *
 * On errors, this class throws a CEFormatException with the following detail
 * strings:
 * <pre>
 *    "BASE64Decoder: Not enough bytes for an atom."
 * </pre>
 *
 * @author      Chuck McManis
 * @see         CharacterEncoder
 * @see         BASE64Decoder
 */

public class BASE64Decoder extends CharacterDecoder {

    /** This class has 4 bytes per atom */
    protected int bytesPerAtom() {
        return (4);
    }

    /** Any multiple of 4 will do, 72 might be common */
    protected int bytesPerLine() {
        return (72);
    }

    /**
     * This character array provides the character to value map
     * based on RFC1521.
     */
    private final static char pem_array[] = {
        //       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
        };

    private final static byte pem_convert_array[] = new byte[256];

    static {
        for (int i = 0; i < 255; i++) {
            pem_convert_array[i] = -1;
        }
        for (int i = 0; i < pem_array.length; i++) {
            pem_convert_array[pem_array[i]] = (byte) i;
        }
    }

    byte decode_buffer[] = new byte[4];

    /**
     * Decode one BASE64 atom into 1, 2, or 3 bytes of data.
     */
    @SuppressWarnings("fallthrough")
    protected void decodeAtom(PushbackInputStream inStream, OutputStream outStream, int rem)
        throws java.io.IOException
    {
        int     i;
        byte    a = -1, b = -1, c = -1, d = -1;

        if (rem < 2) {
            throw new CEFormatException("BASE64Decoder: Not enough bytes for an atom.");
        }
        do {
            i = inStream.read();
            if (i == -1) {
                throw new CEStreamExhausted();
            }
        } while (i == '\n' || i == '\r');
        decode_buffer[0] = (byte) i;

        i = readFully(inStream, decode_buffer, 1, rem-1);
        if (i == -1) {
            throw new CEStreamExhausted();
        }

        if (rem > 3 && decode_buffer[3] == '=') {
            rem = 3;
        }
        if (rem > 2 && decode_buffer[2] == '=') {
            rem = 2;
        }
        switch (rem) {
        case 4:
            d = pem_convert_array[decode_buffer[3] & 0xff];
            // NOBREAK
        case 3:
            c = pem_convert_array[decode_buffer[2] & 0xff];
            // NOBREAK
        case 2:
            b = pem_convert_array[decode_buffer[1] & 0xff];
            a = pem_convert_array[decode_buffer[0] & 0xff];
            break;
        }

        switch (rem) {
        case 2:
            outStream.write( (byte)(((a << 2) & 0xfc) | ((b >>> 4) & 3)) );
            break;
        case 3:
            outStream.write( (byte) (((a << 2) & 0xfc) | ((b >>> 4) & 3)) );
            outStream.write( (byte) (((b << 4) & 0xf0) | ((c >>> 2) & 0xf)) );
            break;
        case 4:
            outStream.write( (byte) (((a << 2) & 0xfc) | ((b >>> 4) & 3)) );
            outStream.write( (byte) (((b << 4) & 0xf0) | ((c >>> 2) & 0xf)) );
            outStream.write( (byte) (((c << 6) & 0xc0) | (d  & 0x3f)) );
            break;
        }
        return;
    }
}

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