imagepreview.java

MyDownloader 是一款使用 http 协议(RFC 1867)用于下载一个或多个文件到本地的简单易用的收费 Java 程序.使用托拽操作,你可以在一个页面内下载多个文件.在下载文件的过程当中

/*
 * Copyright 2006-2007 JavaAtWork All rights reserved.
 * Use is subject to license terms.
 */
package com.javaatwork.mydownloader.dialog;


import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Image;
import java.net.URL;

import javax.swing.ImageIcon;
import javax.swing.JComponent;
import javax.swing.ListSelectionModel;
import javax.swing.event.ListSelectionEvent;
import javax.swing.event.ListSelectionListener;

import com.javaatwork.mydownloader.DownloadFile;
import com.javaatwork.mydownloader.FileTable;

/**
 * Class for displaying a thumbnail.
 * 
 * @author Johannes Postma
 */
public class ImagePreview extends JComponent implements ListSelectionListener {

	/**
	 * serialVersionUID
	 */
	private static final long serialVersionUID = -1228147931360116788L;

	private ImageIcon thumbnail = null;
	private WorkerThread thread = null;
	private Object lock = new Object();
	private URL thumbURL = null;
	private FileTable table = null;
	private ListSelectionModel rowSM = null;

	/**
	 * Creates a new ImagePreview.
	 * 
	 * @param table The FileTable.
	 */
	public ImagePreview(FileTable table) {
		this.table = table;
		setPreferredSize(new Dimension(100, 50));
		// setPreferredSize(new Dimension(50, 25));
		// setMaximumSize(new Dimension(50, 25));
		rowSM = table.getSelectionModel();
		rowSM.addListSelectionListener(this);

		thread = new WorkerThread();
		thread.setPriority(Thread.MIN_PRIORITY);
		thread.setDaemon(true);
		thread.start();

	}

	/**
	 * Will be invoked when the value of ListSelectionEvent is changed.
	 * 
	 * @param e ListSelectionEvent
	 */
	public void valueChanged(ListSelectionEvent e) {

		ListSelectionModel lsm = (ListSelectionModel) e.getSource();

		if (lsm.isSelectionEmpty()) {
			synchronized (lock) {				
				thumbURL = null;
				lock.notifyAll();
			}
			
		} else {

			int selectedRow = lsm.getMinSelectionIndex();
			int selectedMaxRow = lsm.getMaxSelectionIndex();

			if (selectedRow == selectedMaxRow) {

				int index = table.getSelectedRow();
				DownloadFile file = table.getDownloadFile(index);

				if (file != null) {
					synchronized (lock) {
						thumbURL = file.getUrl();
						lock.notifyAll();
					}
				} else {
					synchronized (lock) {
						thumbURL = null;
						lock.notifyAll();						
					}
				}

				// multiple selection -> remove icon
			} else {
				synchronized (lock) {
					thumbURL = null;
					lock.notifyAll();
				}
			}

		}
	}

	/**
	 * Paints the component.
	 * 
	 * @param g  Graphics
	 */
	protected void paintComponent(Graphics g) {

		if (thumbnail != null) {
			int x = getWidth() / 2 - thumbnail.getIconWidth() / 2;
			int y = getHeight() / 2 - thumbnail.getIconHeight() / 2;

			if (y < 0) {
				y = 0;
			}

			if (x < 5) {
				x = 5;
			}

			thumbnail.paintIcon(this, g, x, y);
		}
	}

	/**
	 * A thread for reading the images and creating the thumbnails.
	 */
	class WorkerThread extends Thread {

		URL url = null;

		public void run() {

			images: while (true) {

				try {
					
					synchronized (lock) {

						if (thumbURL == null) {

							thumbnail = null;
							repaint();
							
							lock.wait();
							
							continue images;
							
						} else {
							
							// the thumbfile must be read in an not synchronized block otherwise the normal thread will hang
							// therefore a copy must be made of the original thumbfile
							url = thumbURL;
						}
						
					}
					
					ImageIcon tmpIcon = new ImageIcon(url);
					
					// check if the thumbFile has changed
					synchronized (lock) {
						
						if (thumbURL == null || !url.equals(thumbURL)) {
							
							thumbnail = null;
							repaint();
							
							continue images;
						}
					}					
					
					// create thumbnail
					if (tmpIcon.getIconWidth() > 90) {
						thumbnail = new ImageIcon(tmpIcon.getImage().getScaledInstance(90, -1, Image.SCALE_AREA_AVERAGING));
					} else { // no need to miniaturize
						thumbnail = tmpIcon;
					}
					
					synchronized (lock) {
					
						// check if the thumbFile has changed
						if (thumbURL == null || !url.equals(thumbURL)) {
						
							thumbnail = null;
							repaint();
							
						} 
						
						// paint the thumbnail
						else {
							repaint();
							lock.wait();
						}	
					}
				} catch (Exception exc) {
					// do nothing
				}
			}
		}
	}
}