How to save content of JPanel into jpeg or png file

Question

I have to independent classes: Class A and Class B. Each class constructs its own graphical objects:
Class A {
//do something
public void paintComponent(Graphics g)
int x = 0;
int y = 0;
int w = getSize().width;
int h = getSize().height;
bi = new BufferedImage(
w,h,100,BufferedImage.TYPE_INT_RGB);
g2d = bi.createGraphics();
// draw lines
g2d.drawImage(bi,0,0,ww,hh, this);
Class B {
int x = 0;
int y = 0;
int w = getSize().width;
int h = getSize().height;
bi = new BufferedImage(
w,h,100,BufferedImage.TYPE_INT_RGB);
g2d = bi.createGraphics();
// draw lines
g2d.drawImage(bi,0,0,ww,hh, this);
Two buffered images get properly displayed within JPanel component. However, I need to save two those results into one file. If I add saving file routine into every class, at best I can only get them to be in two different files.
Please let me know if anyone can help me with this problem.
Thanks,
Jack

Answer 1

You didn't mention what should be the format of file that the combines the images. Here are two options:
1. Create another BufferedImage, and draw the BufferedImages from class A and B over this BufferedImage and save it as JPEG or PNG.
In each of the class, you can add a method like getBufferedImage(), which would return the local BufferedImage. A third class, say class C, needs to call this method in each of the classes, and then draw the BufferedImages returned by these methods over another BufferedImage. Save this BufferedImage as a JPEG or PNG.
A disadvantage of this approach is that you can't easily retrieve the individual images from the resulting file.
2. Create a single zip file by adding the individual JPEG/ PNG images created from the BufferedImage in class A and B.
Here is an example that creates single zip file of JPEG images from an array of BufferedImageObjects:
public static void zip(String outfile, BufferedImage bufimage[]){
     if(bufimage == null) return;
     try{
         File of = outfile.endsWith(".zip")? new File(outfile): new File(outfile+".zip");
         FileOutputStream fos = new FileOutputStream(of);
         ZipOutputStream zos = new ZipOutputStream(fos);
         for(int i=0;i<bufimage.length;i++){
             try{
                ByteArrayOutputStream boutstream = new ByteArrayOutputStream();
                JPEGImageEncoder enc = JPEGCodec.createJPEGEncoder(boutstream);
                enc.encode(bufimage);
ZipEntry entry = new ZipEntry("bufimage"+(new Integer(i)).toString()+".jpg");
entry.setMethod(ZipEntry.DEFLATED);
zos.putNextEntry(entry);
byte[] fileBuf = boutstream.toByteArray();
zos.write(fileBuf,0,fileBuf.length);
zos.closeEntry();
} catch (Exception e){ e.printStackTrace();}
zos.flush();
zos.close();
}catch(Exception e) {e.printStackTrace();}
The above method uses the JPEG codec and the zip package, both of which available in J2SE. In other words, you need to import com.sun.image.codec.jpeg and java.util.zip packages.
With this approach, you can easily retrieve the individual JPEGs using the java.util.zip package.