I also use the selenium webdriver and java, and had the same problem.
What i do is copying the path to the file in the clipboard and then paste it in the "open" window and click "Enter". This is working because the focus is always in the "open" button.
Here is the code:
You will need these classes and method:
import java.awt.Robot;
import java.awt.event.KeyEvent;
import java.awt.Toolkit;
import java.awt.datatransfer.StringSelection;
public static void setClipboardData(String string) {
StringSelection stringSelection = new StringSelection(string);
Toolkit.getDefaultToolkit().getSystemClipboard().setContents(stringSelection, null);
}
And that is what i do, just after opening the "open" window:
setClipboardData("C:\\path to file\\example.jpg");
//native key strokes for CTRL, V and ENTER keys
Robot robot = new Robot();
robot.keyPress(KeyEvent.VK_CONTROL);
robot.keyPress(KeyEvent.VK_V);
robot.keyRelease(KeyEvent.VK_V);
robot.keyRelease(KeyEvent.VK_CONTROL);
robot.keyPress(KeyEvent.VK_ENTER);
robot.keyRelease(KeyEvent.VK_ENTER);
And that´s it. It is working for me, i hope it works for some of you.