Getting a BufferedImage as a resource so it will work in JAR file

Question

I'm trying to load an image into my java application as a BufferedImage, with the intent of having it work in a JAR file. I tried using ImageIO.read(new File("images/grass.png")); which worked in the IDE, but not in the JAR.

I've also tried

(BufferedImage) new ImageIcon(getClass().getResource(
            "/images/grass.png")).getImage();

which won't even work in the IDE because of a NullPointerException. I tried doing it with ../images, /images, and images in the path. None of those work.

Am I missing something here?

Answer 1

new File("images/grass.png") looks for a directory images on the file system, in the current directory, which is the directory from which the application is started. So that's wrong.

ImageIO.read() returns a BufferedImage, and takes a URL or an InputStream as argument. To get an URL of InputStream from the classpath, you use Class.getResource() or Class.getResourceAsStream(). And the path starts with a /, and starts at the root of the classpath.

So, the following code should work if the grass.png file is under the package images in the classpath:

BufferedImage image = ImageIO.read(MyClass.class.getResourceAsStream("/images/grass.png"));

This will work in the IDE is the file is in the runtime classpath. And it will be if the IDE "compiles" it to its target classes directory. To do that, the file must be under a sources directory, along with your Java source files.