JDK8/Java8源码在线阅读

/*
 * Copyright (c) 1995, 1997, 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.InputStream;
import java.io.PrintStream;
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.
 *
 * @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)]);

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