BASE64Encoder 与 BASE64Decoder 源代码

package com.example.rsa_android; /* 2 * Copyright (c) 1995, 2005, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ import java.io.InputStream; import java.io.ByteArrayInputStream; import java.io.OutputStream; import java.io.ByteArrayOutputStream; import java.io.PrintStream; import java.io.IOException; import java.nio.ByteBuffer; /** 38 * This class defines the encoding half of character encoders. 39 * A character encoder is an algorithim for transforming 8 bit binary 40 * data into text (generally 7 bit ASCII or 8 bit ISO-Latin-1 text) 41 * for transmition over text channels such as e-mail and network news. 42 * 43 * The character encoders have been structured around a central theme 44 * that, in general, the encoded text has the form: 45 * 46 * <pre> 47 * [Buffer Prefix] 48 * [Line Prefix][encoded data atoms][Line Suffix] 49 * [Buffer Suffix] 50 * </pre> 51 * 52 * In the CharacterEncoder and CharacterDecoder classes, one complete 53 * chunk of data is referred to as a <i>buffer</i>. Encoded buffers 54 * are all text, and decoded buffers (sometimes just referred to as 55 * buffers) are binary octets. 56 * 57 * To create a custom encoder, you must, at a minimum, overide three 58 * abstract methods in this class. 59 * <DL> 60 * <DD>bytesPerAtom which tells the encoder how many bytes to 61 * send to encodeAtom 62 * <DD>encodeAtom which encodes the bytes sent to it as text. 63 * <DD>bytesPerLine which tells the encoder the maximum number of 64 * bytes per line. 65 * </DL> 66 * 67 * Several useful encoders have already been written and are 68 * referenced in the See Also list below. 69 * 70 * @author Chuck McManis 71 * @see CharacterDecoder; 72 * @see UCEncoder 73 * @see UUEncoder 74 * @see BASE64Encoder 75 */ public abstract class CharacterEncoder { /** Stream that understands "printing" */ protected PrintStream pStream; /** Return the number of bytes per atom of encoding */ abstract protected int bytesPerAtom(); /** Return the number of bytes that can be encoded per line */ abstract protected int bytesPerLine(); /** * Encode the prefix for the entire buffer. By default is simply * opens the PrintStream for use by the other functions. */ protected void encodeBufferPrefix(OutputStream aStream) throws IOException { pStream = new PrintStream(aStream); } /** * Encode the suffix for the entire buffer. */ protected void encodeBufferSuffix(OutputStream aStream) throws IOException { } /** * Encode the prefix that starts every output line. */ protected void encodeLinePrefix(OutputStream aStream, int aLength) throws IOException { } /** * Encode the suffix that ends every output line. By default * this method just prints a <newline> into the output stream. */ protected void encodeLineSuffix(OutputStream aStream) throws IOException { pStream.println(); } /** Encode one "atom" of information into characters. */ abstract protected void encodeAtom(OutputStream aStream, byte someBytes[], int anOffset, int aLength) throws IOException; /** * This method works around the bizarre semantics of BufferedInputStream's * read method. */ protected int readFully(InputStream in, byte buffer[]) throws java.io.IOException { for (int i = 0; i < buffer.length; i++) { int q = in.read(); if (q == -1) return i; buffer[i] = (byte)q; } return buffer.length; } /** * Encode bytes from the input stream, and write them as text characters * to the output stream. This method will run until it exhausts the * input stream, but does not print the line suffix for a final * line that is shorter than bytesPerLine(). */ public void encode(InputStream inStream, OutputStream outStream) throws IOException { int j; int numBytes; byte tmpbuffer[] = new byte[bytesPerLine()]; encodeBufferPrefix(outStream); while (true) { numBytes = readFully(inStream, tmpbuffer); if (numBytes == 0) { break; } encodeLinePrefix(outStream, numBytes); for (j = 0; j < numBytes; j += bytesPerAtom()) { if ((j + bytesPerAtom()) <= numBytes) { encodeAtom(outStream, tmpbuffer, j, bytesPerAtom()); } else { encodeAtom(outStream, tmpbuffer, j, (numBytes)- j); } } if (numBytes < bytesPerLine()) { break; } else { encodeLineSuffix(outStream); } } encodeBufferSuffix(outStream); } /** * Encode the buffer in <i>aBuffer</i> and write the encoded * result to the OutputStream <i>aStream</i>. */ public void encode(byte aBuffer[], OutputStream aStream) throws IOException { ByteArrayInputStream inStream = new ByteArrayInputStream(aBuffer); encode(inStream, aStream); } /** * A 'streamless' version of encode that simply takes a buffer of * bytes and returns a string containing the encoded buffer. */ public String encode(byte aBuffer[]) { ByteArrayOutputStream outStream = new ByteArrayOutputStream(); ByteArrayInputStream inStream = new ByteArrayInputStream(aBuffer); String retVal = null; try {