JImagePreviewPanel.java

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package org.demo.fileViewer;

import java.awt.Graphics;
import java.awt.image.BufferedImage;
import javax.swing.JPanel;

/**
 *
 * @author ECO
 */
public class JImagePreviewPanel extends JPanel {

    public BufferedImage getImage() {
        return image;
    }

    public void setImage(BufferedImage image) {
        this.image = image;
        this.repaint();
    }
    private BufferedImage image;

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);

        if (image != null) {
            final int W0=getWidth();
            final int H0=getHeight();

            final int imgWidth = image.getWidth(this);
            final int imgHeight = image.getHeight(this);

            int calcWidth;
            int calcHeight;

            if (imgWidth < W0 && imgHeight < H0) {
                calcWidth = imgWidth;
                calcHeight = imgHeight;
            } else {
                final float scale = Math.min((float)W0 / (float)imgWidth, (float)H0 / (float)imgHeight);
                calcWidth = (int)Math.min(imgWidth * scale, W0);
                calcHeight = (int)Math.min(imgHeight * scale, H0);
            }
            final int X1 = (W0 - calcWidth) / 2;
            final int Y1 = (H0 - calcHeight) / 2;

            g.drawImage(image, X1, Y1, calcWidth, calcHeight, this);
        }
    }
}