ClassLoader.getSystemClassLoader().getResourceAsStream 在克隆项目后返回 null

Question

I've been applying the solutions from other similar questions.

I was getting a image from res folder using this line:

shell.setImage(new Image(display, ClassLoader.getSystemClassLoader().getResourceAsStream("icon_128.png")));

The file is inside "res" folder in the project.

It worked perfectly until I uploaded my project to a Git repo in Bitbucket. After cloning the project and importing it, now my project crash because getResourceAsStream("icon_128.png") returns null.

It's frustrating because it works perfectly in the other project which is not versioned into G|it, but crashes only in my cloned new directory project with Git.

In both versions of the project the file is inside the "res" folder.

What could be happening with this?

Answer 1

git has nothing to do with it. You didn't give enough detail to be sure about what's going on, but 2 obvious problems come to mind:

[1] getResourceAsStream looks for the named file in the same place that java looks for class files: The classpath. You're running this code either from an editor, or with java on the command line (in which case you're running a jar file and a build tool added a Class-Path entry to that jar, if you use the -jar switch, or you're not, in which case you're specifying the classpath on the command line), or with a build tool (in which case it will be supplying the classpath): icon_128.png needs to be in the root of one of the entries on the classpath, and now it isn't. The fix is to, well, fix that. Maven, for example, copies all resources find in /src/main/resources into any jars it makes. Your icon_128.png should be there.

[2] This isn't the right way to do it. The right way is ClassThisCodeIsIn.class.getResourceAsStream("/icon_128.png") (note: The starting slash; it is important). Your version has various somewhat exotic fail cases which this version skips. This version will look specifically in the classpath which produced your class file, and cannot NPE; your version will fail or throw NullPointerExceptions in various cases.

NB: When you cloned and re-built, the 'build' directories were effectively wiped because you don't check those into source control. That's why it worked before and doesn't now. git isn't to blame; you, or your IDE, copied icon_128.png to the build dir, and that step needs to be repeated every time you clone your git repo. A build tool automates this step and ensures that you can just do a fresh checkout from source control, and then invoke the build tool and all will be well after it finishes.