Java screenshot of certain App in MacOS

Question

I want to take screenshot of certain app in my MacOS, even if on another virtual screen and not in active screen.

I can take active screen capture with following code but how to capture given application?

import java.awt.AWTException;
import java.awt.Robot;
import java.awt.Rectangle;
import java.awt.Toolkit;
import java.awt.image.BufferedImage;
import java.io.*;
import java.text.SimpleDateFormat;
import java.util.Date;
import javax.imageio.ImageIO;

public class Screenshot {
    public static void main(String args[]) throws AWTException, IOException {
        while(true) {
            String timeStamp = new SimpleDateFormat("yyyy-MM-dd_HH-mm-ss").format(new Date());

            BufferedImage screencapture = new Robot().createScreenCapture(
                new Rectangle(Toolkit.getDefaultToolkit().getScreenSize())
            );

            // Save as JPEG
            File file = new File("./screens/screencapture" + timeStamp + ".jpg");
            ImageIO.write(screencapture, "jpg", file);

            try {
                Thread.sleep(1000);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
}

Answer 1

Try using /usr/sbin/screencapture, and calling it with

Runtime.getRuntime().exec("/usr/sbin/screencapture");

Here is the usage output of screencapture

usage: screencapture [-icMPmwsWxSCUtoa] [files]
  -c         force screen capture to go to the clipboard
  -C         capture the cursor as well as the screen. only in non-interactive modes
  -d         display errors to the user graphically
  -i         capture screen interactively, by selection or window
               control key - causes screen shot to go to clipboard
               space key   - toggle between mouse selection and
                             window selection modes
               escape key  - cancels interactive screen shot
  -m         only capture the main monitor, undefined if -i is set
  -M         screen capture output will go to a new Mail message
  -o         in window capture mode, do not capture the shadow of the window
  -P         screen capture output will open in Preview
  -s         only allow mouse selection mode
  -S         in window capture mode, capture the screen not the window
  -t<format> image format to create, default is png (other options include pdf, jpg, tiff and other formats)
  -T<seconds> Take the picture after a delay of <seconds>, default is 5
  -w         only allow window selection mode
  -W         start interaction in window selection mode
  -x         do not play sounds
  -a         do not include windows attached to selected windows
  -r         do not add dpi meta data to image
  -l<windowid> capture this windowsid
  -R<x,y,w,h> capture screen rect
  files   where to save the screen capture, 1 file per screen

I think the -w option with window id is the one to use. But to get the window id, you will probably need another utility. One such utility is pyscreencapture. Otherwise I am sure googling how to get the window id will result in more ways to get the window id you require.

Though I am not entirely sure what you mean by virtual screen, and you may have problem with obtaining the window id or capturing the screen.