import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import java.awt.image.RenderedImage;
import java.io.File;
import java.util.Iterator;

import javax.imageio.IIOImage;
import javax.imageio.ImageIO;
import javax.imageio.ImageWriteParam;
import javax.imageio.ImageWriter;
import javax.imageio.stream.FileImageOutputStream;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

class SpeichereComponenteALsBildClass implements ActionListener {

    private JPanel jpanel;
    private String fileName = "/Users/joecze/Desktop/SaveComponent.jpg";

    public SpeichereComponenteALsBildClass() {
        init();
    }
    
    private void init() {
        JFrame frame = new JFrame("Komponente als Bild");
        jpanel = new JPanel();
        JButton b = new JButton("Save me!");
        b.addActionListener(this);
        jpanel.add(b);
        frame.setSize(300, 300);
        frame.add(jpanel);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }
    
    private void saveCompAsImg() {
        // Erstelle ein BufferedImage
        int w = jpanel.getWidth();
        int h = jpanel.getHeight();
        float quality = 1f;
        BufferedImage bi = new BufferedImage(w, h, BufferedImage.TYPE_INT_RGB);
        Graphics2D big2d = bi.createGraphics();

        // Male das JPanel in das BufferedImage
        jpanel.paint(big2d);

        Iterator<ImageWriter> iter = ImageIO
                .getImageWritersByFormatName("jpeg");
        ImageWriter writer = (ImageWriter) iter.next();
        ImageWriteParam iwp = writer.getDefaultWriteParam();
        iwp.setCompressionMode(ImageWriteParam.MODE_EXPLICIT);
        iwp.setCompressionQuality(quality);

        try {
            FileImageOutputStream fos = new FileImageOutputStream(new File(
                    fileName));
            writer.setOutput(fos);
            IIOImage img = new IIOImage((RenderedImage) bi, null, null);
            writer.write(null, img, iwp);

        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }

    public void actionPerformed(ActionEvent e) {
        saveCompAsImg();
    }
    
    public static void main(String args[]) {
        SwingUtilities.invokeLater(() -> new SpeichereComponenteALsBildClass());
    }
}