sizedocumentfilter.java

google公司的用Java写的一个聊天软件的原代码

/***************************************************************************
 *   Copyright 2006-2008 by Christian Ihle                                 *
 *   [e-mail]                                                  *
 *                                                                         *
 *   This program is free software; you can redistribute it and/or modify  *
 *   it under the terms of the GNU General Public License as published by  *
 *   the Free Software Foundation; either version 2 of the License, or     *
 *   (at your option) any later version.                                   *
 *                                                                         *
 *   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 for more details.                          *
 *                                                                         *
 *   You should have received a copy of the GNU General Public License     *
 *   along with this program; if not, write to the                         *
 *   Free Software Foundation, Inc.,                                       *
 *   59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.             *
 ***************************************************************************/

package net.usikkert.kouchat.ui.swing;

import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.DocumentFilter;

import net.usikkert.kouchat.util.Tools;

/**
 * Limits the number of bytes a Document can contain.
 * Practical for use in the text field where users write
 * messages to send, so they know when a message is too
 * long before it is sent.
 *
 * @author Christian Ihle
 */
public class SizeDocumentFilter extends DocumentFilter
{
	private int maxBytes;

	/**
	 * Constructor.
	 *
	 * @param maxBytes The maximum number of bytes the
	 * Document can contain.
	 */
	public SizeDocumentFilter( final int maxBytes )
	{
		this.maxBytes = maxBytes;
	}

	/**
	 * Replaces the parts of the text that fits within the byte limit.
	 * This got a bit more complicated than I thought, because of the varying
	 * size of characters in different character sets.
	 *
	 * Also removes tabs and newlines.
	 */
	@Override
	public void replace( final FilterBypass fb, final int offset, final int length,
			final String text, final AttributeSet attrs ) throws BadLocationException
	{
		if ( text != null && text.length() > 0 )
		{
			String newText = text;

			// Replace newlines with space
			if ( newText.contains( "\n" ) )
				newText = newText.replace( '\n', ' ' );

			// Replace tabs with space
			if ( newText.contains( "\t" ) )
				newText = newText.replace( '\t', ' ' );

			String docText = fb.getDocument().getText( 0, fb.getDocument().getLength() );
			int textLength = Tools.getBytes( newText );
			int docLength = Tools.getBytes( docText );
			int removedLength = Tools.getBytes( docText.substring( offset, offset + length ) );

			// Everything OK, insert the text as it is.
			if ( ( docLength + textLength - removedLength ) <= maxBytes )
			{
				super.replace( fb, offset, length, newText, attrs );
			}

			// Text too big to fit. Will need to find out which
			// characters that can be inserted without going over the limit.
			else
			{
				String replaceText = "";
				int replaceTextSize = 0;
				int allowedSize = maxBytes - docLength;

				for ( int i = 0; i < newText.length(); i++ )
				{
					if ( replaceTextSize < allowedSize )
					{
						String tmpChar = "" + newText.charAt( i );
						int tmpCharSize = Tools.getBytes( tmpChar );

						if ( replaceTextSize + tmpCharSize <= allowedSize )
						{
							replaceText += tmpChar;
							replaceTextSize += tmpCharSize;
						}

						else
							break;
					}

					else
						break;
				}

				super.replace( fb, offset, length, replaceText, attrs );
			}
		}

		// Empty text, just continue normally.
		else
		{
			super.replace( fb, offset, length, text, attrs );
		}
	}
}