Java example source code file (AbstractFilter.java)

This example Java source code file (AbstractFilter.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

abstractfilter, ioexception, outputstream, stringbuilder

The AbstractFilter.java Java example source code

/*
 * Copyright (c) 1997, 2010, 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 javax.swing.text.rtf;

import java.io.*;
import java.lang.*;

/**
 * A generic superclass for streams which read and parse text
 * consisting of runs of characters interspersed with occasional
 * ``specials'' (formatting characters).
 *
 * <p> Most of the functionality
 * of this class would be redundant except that the
 * <code>ByteToChar converters
 * are suddenly private API. Presumably this class will disappear
 * when the API is made public again. (sigh) That will also let us handle
 * multibyte character sets...
 *
 * <P> A subclass should override at least write(char)
 * and <code>writeSpecial(int). For efficiency's sake it's a
 * good idea to override <code>write(String) as well. The subclass'
 * initializer may also install appropriate translation and specials tables.
 *
 * @see OutputStream
 */
abstract class AbstractFilter extends OutputStream
{
    /** A table mapping bytes to characters */
    protected char translationTable[];
    /** A table indicating which byte values should be interpreted as
     *  characters and which should be treated as formatting codes */
    protected boolean specialsTable[];

    /** A translation table which does ISO Latin-1 (trivial) */
    static final char latin1TranslationTable[];
    /** A specials table which indicates that no characters are special */
    static final boolean noSpecialsTable[];
    /** A specials table which indicates that all characters are special */
    static final boolean allSpecialsTable[];

    static {
      int i;

      noSpecialsTable = new boolean[256];
      for (i = 0; i < 256; i++)
        noSpecialsTable[i] = false;

      allSpecialsTable = new boolean[256];
      for (i = 0; i < 256; i++)
        allSpecialsTable[i] = true;

      latin1TranslationTable = new char[256];
      for (i = 0; i < 256; i++)
        latin1TranslationTable[i] = (char)i;
    }

    /**
     * A convenience method that reads text from a FileInputStream
     * and writes it to the receiver.
     * The format in which the file
     * is read is determined by the concrete subclass of
     * AbstractFilter to which this method is sent.
     * <p>This method does not close the receiver after reaching EOF on
     * the input stream.
     * The user must call <code>close() to ensure that all
     * data are processed.
     *
     * @param in      An InputStream providing text.
     */
    public void readFromStream(InputStream in)
      throws IOException
    {
        byte buf[];
        int count;

        buf = new byte[16384];

        while(true) {
            count = in.read(buf);
            if (count < 0)
                break;

            this.write(buf, 0, count);
        }
    }

    public void readFromReader(Reader in)
      throws IOException
    {
        char buf[];
        int count;

        buf = new char[2048];

        while(true) {
            count = in.read(buf);
            if (count < 0)
                break;
            for (int i = 0; i < count; i++) {
              this.write(buf[i]);
            }
        }
    }

    public AbstractFilter()
    {
        translationTable = latin1TranslationTable;
        specialsTable = noSpecialsTable;
    }

    /**
     * Implements the abstract method of OutputStream, of which this class
     * is a subclass.
     */
    public void write(int b)
      throws IOException
    {
      if (b < 0)
        b += 256;
      if (specialsTable[b])
        writeSpecial(b);
      else {
        char ch = translationTable[b];
        if (ch != (char)0)
          write(ch);
      }
    }

    /**
     * Implements the buffer-at-a-time write method for greater
     * efficiency.
     *
     * <p> PENDING: Does write(byte[])
     * call <code>write(byte[], int, int) or is it the other way
     * around?
     */
    public void write(byte[] buf, int off, int len)
      throws IOException
    {
      StringBuilder accumulator = null;
      while (len > 0) {
        short b = (short)buf[off];

        // stupid signed bytes
        if (b < 0)
            b += 256;

        if (specialsTable[b]) {
          if (accumulator != null) {
            write(accumulator.toString());
            accumulator = null;
          }
          writeSpecial(b);
        } else {
          char ch = translationTable[b];
          if (ch != (char)0) {
            if (accumulator == null)
              accumulator = new StringBuilder();
            accumulator.append(ch);
          }
        }

        len --;
        off ++;
      }

      if (accumulator != null)
        write(accumulator.toString());
    }

    /**
     * Hopefully, all subclasses will override this method to accept strings
     * of text, but if they don't, AbstractFilter's implementation
     * will spoon-feed them via <code>write(char).
     *
     * @param s The string of non-special characters written to the
     *          OutputStream.
     */
    public void write(String s)
      throws IOException
    {
      int index, length;

      length = s.length();
      for(index = 0; index < length; index ++) {
        write(s.charAt(index));
      }
    }

    /**
     * Subclasses must provide an implementation of this method which
     * accepts a single (non-special) character.
     *
     * @param ch The character written to the OutputStream.
     */
    protected abstract void write(char ch) throws IOException;

    /**
     * Subclasses must provide an implementation of this method which
     * accepts a single special byte. No translation is performed
     * on specials.
     *
     * @param b The byte written to the OutputStream.
     */
    protected abstract void writeSpecial(int b) throws IOException;
}