java.lang.IllegalArgumentException：输入== null！ 在javax.imageio.ImageIO.read（未知来源）

Question

I am trying to set the icon image like

private void formWindowActivated(java.awt.event.WindowEvent evt) {                                     
  try {

        Image img=ImageIO.read(getClass().getResource("images/logo.png"));
        setIconImage(img);
    } catch (IOException ex) {
        System.out.println(ex.getMessage());
    }
}   

The code seems to work perfectly after compilation on NetBeans but I get the IllegalArgumentException if I run the jar file from cmd.I don't seem to understand how the image can be visible in first case and not on the other one.

Answer 1

This will happen under Windows (case insensitive file system) where loading may succeed for say Images/Logo.PNG on the unpacked class path, and will fail when starting from the jar (zip Archive), where paths are case-sensitive.

Correcting the case of a file may be cumbersome (version control and such), hence a rename might be more useful.

Remarks:

If the (actual!) class is in package xyz , the directory path in the jar is x/y/z/images/logo.png .

Hence alternatives to consider are non-child class reference and absolute path:

    Image img=ImageIO.read(Xyz.class.getResource("images/logo.png"));
    Image img=ImageIO.read(getClass().getResource("/u/v/w/images/logo.png"));