base64encoder.java

来自「This is a resource based on j2me embedde」· Java 代码 · 共 115 行

/*
 * @(#)BASE64Encoder.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.IOException;

/**
 * This class implements a BASE64 Character encoder as specified in RFC1521.
 * This RFC is part of the MIME specification as published by the Internet 
 * Engineering Task Force (IETF). Unlike some other encoding schemes there 
 * is nothing in this encoding that indicates
 * where a buffer starts or ends.
 *
 * This means that the encoded text will simply start with the first line
 * of encoded text and end with the last line of encoded text.
 *
 * @version	1.19, 02/02/00
 * @author	Chuck McManis
 * @see		CharacterEncoder
 * @see		BASE64Decoder
 */

public class BASE64Encoder extends CharacterEncoder {
	
    /** this class encodes three bytes per atom. */
    protected int bytesPerAtom() {
	return (3);
    }

    /** 
     * this class encodes 57 bytes per line. This results in a maximum
     * of 57/3 * 4 or 76 characters per output line. Not counting the
     * line termination.
     */
    protected int bytesPerLine() {
	return (57);
    }

    /** This array maps the characters to their 6 bit values */
    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
	};

    /** 
     * encodeAtom - Take three bytes of input and encode it as 4
     * printable characters. Note that if the length in len is less
     * than three is encodes either one or two '=' signs to indicate
     * padding characters.
     */
    protected void encodeAtom(OutputStream outStream, byte data[], int offset, int len) 
	throws IOException {
	byte a, b, c;

	if (len == 1) {
	    a = data[offset];
	    b = 0;
	    c = 0;
	    outStream.write(pem_array[(a >>> 2) & 0x3F]);
	    outStream.write(pem_array[((a << 4) & 0x30) + ((b >>> 4) & 0xf)]);
	    outStream.write('=');
	    outStream.write('=');
	} else if (len == 2) {
	    a = data[offset];
	    b = data[offset+1];
	    c = 0;
	    outStream.write(pem_array[(a >>> 2) & 0x3F]);
	    outStream.write(pem_array[((a << 4) & 0x30) + ((b >>> 4) & 0xf)]);
	    outStream.write(pem_array[((b << 2) & 0x3c) + ((c >>> 6) & 0x3)]);
	    outStream.write('=');
	} else {
	    a = data[offset];
	    b = data[offset+1];
	    c = data[offset+2];
	    outStream.write(pem_array[(a >>> 2) & 0x3F]);
	    outStream.write(pem_array[((a << 4) & 0x30) + ((b >>> 4) & 0xf)]);
	    outStream.write(pem_array[((b << 2) & 0x3c) + ((c >>> 6) & 0x3)]);
	    outStream.write(pem_array[c & 0x3F]);
	}
    }
}