您好 Java 开发人员,
所以我最近遇到了这个问题。这是和SSCCE:
public class SampleClass extends JPanel{
    private Image img;
    private final String IMG_DIRECTORY = ("/res/BG.png");
    public SampleClass(){
        try{
            img = ImageIO.read(getClass().getResource(IMG_DIRECTORY));
        } catch (IOException ioEx) {
            ioEx.printStackTrace();
        }
    }
    @Override
    public void paintComponent(Graphics g){
        super.paintComponent(g);
        g.drawImage(img, 0, 0, null);
    }
}
此行抛出异常
img = ImageIO.read(getClass().getResource(IMG_DIRECTORY));
这是堆栈跟踪:
Exception in thread "main" java.lang.IllegalArgumentException: input == null!
    at javax.imageio.ImageIO.read(Unknown Source)
    at com.forte.project.chatservice.uicomponent.FrameBackground.<init>(FrameBackground.java:27)
    at com.forte.project.chatservice.ui.MainFrame.<init>(MainFrame.java:27)
    at com.forte.project.chatservice.ChatService.main(ChatService.java:18)
我做了以下事情:
- 谷歌。
- 更新了我的 Java 
- .getResourceAsStream(IMG_DIRECTORY); 
- this.getClass().getResource(IMG_DIRECTORY)); 
- MainClass.class.getClass().getResource(IMG_DIRECTORY);