base64decoder.java

来自「This is a resource based on j2me embedde」· Java 代码 · 共 166 行

/*
 * @(#)BASE64Decoder.java	1.25 06/10/10
 *
 * Copyright  1990-2008 Sun Microsystems, Inc. All Rights Reserved.  
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER  
 *   
 * This program 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.   
 *   
 * This program 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 at /legal/license.txt).   
 *   
 * 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 Sun Microsystems, Inc., 4150 Network Circle, Santa  
 * Clara, CA 95054 or visit www.sun.com if you need additional  
 * information or have any questions. 
 *
 */
package sun.misc;

import java.io.OutputStream;
import java.io.InputStream;
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</i> and give you an array 
 * of bytes in the array <i>myData</i>. 
 *
 * On errors, this class throws a CEFormatException with the following detail
 * strings:
 * <pre>
 *    "BASE64Decoder: Not enough bytes for an atom."
 * </pre>
 *
 * @version	1.19, 02/02/00
 * @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.
     */
    protected void decodeAtom(InputStream 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;
    }
}