LimitLinesDocumentListener.java

/*******************************************************************************
 * Copyright 2015 Maximilian Stark | Dakror <mail@dakror.de>
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *   http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 ******************************************************************************/


package de.dakror.arise.ui;

import javax.swing.SwingUtilities;
import javax.swing.event.DocumentEvent;
import javax.swing.event.DocumentListener;
import javax.swing.text.BadLocationException;
import javax.swing.text.Document;
import javax.swing.text.Element;

/*
 * A class to control the maximum number of lines to be stored in a Document
 * Excess lines can be removed from the start or end of the Document
 * depending on your requirement.
 * a) if you append text to the Document, then you would want to remove lines
 * from the start.
 * b) if you insert text at the beginning of the Document, then you would
 * want to remove lines from the end.
 */
public class LimitLinesDocumentListener implements DocumentListener {
	private int maximumLines;
	private boolean isRemoveFromStart;
	
	/*
	 * Specify the number of lines to be stored in the Document.
	 * Extra lines will be removed from the start of the Document.
	 */
	public LimitLinesDocumentListener(int maximumLines) {
		this(maximumLines, true);
	}
	
	/*
	 * Specify the number of lines to be stored in the Document.
	 * Extra lines will be removed from the start or end of the Document,
	 * depending on the boolean value specified.
	 */
	public LimitLinesDocumentListener(int maximumLines, boolean isRemoveFromStart) {
		setLimitLines(maximumLines);
		this.isRemoveFromStart = isRemoveFromStart;
	}
	
	/*
	 * Return the maximum number of lines to be stored in the Document
	 */
	public int getLimitLines() {
		return maximumLines;
	}
	
	/*
	 * Set the maximum number of lines to be stored in the Document
	 */
	public void setLimitLines(int maximumLines) {
		if (maximumLines < 1) {
			String message = "Maximum lines must be greater than 0";
			throw new IllegalArgumentException(message);
		}
		
		this.maximumLines = maximumLines;
	}
	
	// Handle insertion of new text into the Document
	
	@Override
	public void insertUpdate(final DocumentEvent e) {
		// Changes to the Document can not be done within the listener
		// so we need to add the processing to the end of the EDT
		
		SwingUtilities.invokeLater(new Runnable() {
			@Override
			public void run() {
				removeLines(e);
			}
		});
	}
	
	@Override
	public void removeUpdate(DocumentEvent e) {}
	
	@Override
	public void changedUpdate(DocumentEvent e) {}
	
	/*
	 * Remove lines from the Document when necessary
	 */
	private void removeLines(DocumentEvent e) {
		// The root Element of the Document will tell us the total number
		// of line in the Document.
		
		Document document = e.getDocument();
		Element root = document.getDefaultRootElement();
		
		while (root.getElementCount() > maximumLines) {
			if (isRemoveFromStart) {
				removeFromStart(document, root);
			} else {
				removeFromEnd(document, root);
			}
		}
	}
	
	/*
	 * Remove lines from the start of the Document
	 */
	private void removeFromStart(Document document, Element root) {
		Element line = root.getElement(0);
		int end = line.getEndOffset();
		
		try {
			document.remove(0, end);
		} catch (BadLocationException ble) {
			System.out.println(ble);
		}
	}
	
	/*
	 * Remove lines from the end of the Document
	 */
	private void removeFromEnd(Document document, Element root) {
		// We use start minus 1 to make sure we remove the newline
		// character of the previous line
		
		Element line = root.getElement(root.getElementCount() - 1);
		int start = line.getStartOffset();
		int end = line.getEndOffset();
		
		try {
			document.remove(start - 1, end - start);
		} catch (BadLocationException ble) {
			System.out.println(ble);
		}
	}
}