Java Programmer's Toolkit/Java Programmer's Toolkit.iso/hotjava/classsrc/java/util/charac~2.jav

Text File | 1995-08-11 | 5.1 KB | 165 lines

/*
 * @(#)CharacterEncoder.java    1.6 95/04/02 Chuck McManis
 *
 * Copyright (c) 1994 Sun Microsystems, Inc. All Rights Reserved.
 *
 * Permission to use, copy, modify, and distribute this software
 * and its documentation for NON-COMMERCIAL purposes and without
 * fee is hereby granted provided that this copyright notice
 * appears in all copies. Please refer to the file "copyright.html"
 * for further important copyright and licensing information.
 *
 * SUN MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE SUITABILITY OF
 * THE SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
 * TO THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
 * PARTICULAR PURPOSE, OR NON-INFRINGEMENT. SUN SHALL NOT BE LIABLE FOR
 * ANY DAMAGES SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING OR
 * DISTRIBUTING THIS SOFTWARE OR ITS DERIVATIVES.
 */

package java.util;

import java.io.InputStream;
import java.io.InputStreamBuffer;
import java.io.OutputStream;
import java.io.OutputStreamBuffer;
import java.io.PrintStream;


/**
 * This class defines the encoding half of character encoders.
 * A character encoder is an algorithim for transforming 8 bit binary
 * data into text (generally 7 bit ASCII or 8 bit ISO-Latin-1 text)
 * for transmition over text channels such as e-mail and network news.
 *
 * The character encoders have been structured around a central theme
 * that, in general, the encoded text has the form:
 *
 * <pre>
 *    [Buffer Prefix]
 *    [Line Prefix][encoded data atoms][Line Suffix]
 *    [Buffer Suffix]
 * </pre>
 *
 * In the CharacterEncoder and CharacterDecoder classes, one complete
 * chunk of data is referred to as a <i>buffer</i>. Encoded buffers
 * are all text, and decoded buffers (sometimes just referred to as
 * buffers) are binary octets.
 *
 * To create a custom encoder, you must, at a minimum,  overide three
 * abstract methods in this class.
 * <DL>
 * <DD>bytesPerAtom which tells the encoder how many bytes to
 * send to encodeAtom
 * <DD>encodeAtom which encodes the bytes sent to it as text.
 * <DD>bytesPerLine which tells the encoder the maximum number of
 * bytes per line.
 * </DL>
 *
 * Several useful encoders have already been written and are
 * referenced in the See Also list below.
 *
 * @version    02 Apr 1995, 1.6
 * @author    Chuck McManis
 * @see        CharacterDecoder;
 * @see        UCEncoder
 * @see        UUEncoder
 * @see        BASE64Encoder
 */

public class CharacterEncoder {

    /** Stream that understands "printing" */
    protected PrintStream pStream;

    /** Return the number of bytes per atom of encoding */
    abstract int bytesPerAtom();

    /** Return the number of bytes that can be encoded per line */
    abstract int bytesPerLine();

    /**
     * Encode the prefix for the entire buffer. By default is simply
     * opens the PrintStream for use by the other functions.
     */
    void encodeBufferPrefix(OutputStream aStream) {
    pStream = new PrintStream(aStream);
    }

    /**
     * Encode the suffix for the entire buffer.
     */
    void encodeBufferSuffix(OutputStream aStream) { }

    /**
     * Encode the prefix that starts every output line.
     */
    void encodeLinePrefix(OutputStream aStream, int aLength) { }

    /**
     * Encode the suffix that ends every output line. By default
     * this method just prints a <newline> into the output stream.
     */
    void encodeLineSuffix(OutputStream aStream) {
    pStream.println();
    }

    /** Encode one "atom" of information into characters. */
    abstract void encodeAtom(OutputStream aStream, byte someBytes[],
        int anOffset, int aLength);

    /**
     * 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.
     */
    public void encodeBuffer(InputStream inStream, OutputStream outStream) {
    int    j;
    int    numBytes;
    byte    tmpbuffer[] = new byte[bytesPerLine()];

    encodeBufferPrefix(outStream);

    while (true) {
        numBytes = inStream.read(tmpbuffer);
        if (numBytes == -1) {
        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, tmpbuffer.length - j);
        }
        }
        encodeLineSuffix(outStream);
        if (numBytes < bytesPerLine()) {
        break;
        }
    }
    encodeBufferSuffix(outStream);
    }

    /**
     * Encode the buffer in <i>aBuffer</i> and write the encoded
     * result to the OutputStream <i>aStream</i>.
     */
    public void encodeBuffer(byte aBuffer[], OutputStream aStream) {
    InputStreamBuffer inStream = new InputStreamBuffer(aBuffer);
    encodeBuffer(inStream, aStream);
    }

    /**
     * A 'streamless' version of encode that simply takes a buffer of
     * bytes and returns a string containing the encoded buffer.
     */
    public String encodeBuffer(byte aBuffer[]) {
    OutputStreamBuffer    outStream = new OutputStreamBuffer();
    InputStreamBuffer    inStream = new InputStreamBuffer(aBuffer);
    encodeBuffer(inStream, outStream);
    return (outStream.toString());
    }

}