Referencing an image inside a jar file when running junit

Question

I have been playing with the idea of using ImageMagic (im4java) to do a comparison of known good page renders against stored good pages.

I have got this working on a test site, but all my images (good, bad and differrent) are stored in my c:\temp folder. I have been toying with the idea of having the "expected" images kept inside the project folder structure, so when the project is checked out, the expected images are there.

(not saying this is a great solution, this is just something I have been playing with.)

So my test is stored in /src/test/java/my.screen.test/compareTest.java and I have my "expected" image in /masterImages/test.png

I have tried various ways to reference this:

I included masterImages in the build path and then tried to use InputStream input = getClass().getResourceAsStream("/masterImages/googleHomePage1.png"); (I then thought I could simply use input.toString() to pass into im4java - but the InputStream gave me nullpointer exception) I also tried removing the masterImages from the buildpath and trying it that way.

I have also tried String path = getClass().getClassLoader().getResource("masterImages/googleHomePage1.png").toString(); Again, null pointer. I know there is something stupid I am not seeing here, like I said this started as me playing but it's now annoying me why I can't get it to work.

Any insights into what I am missing greatly appreciated.

Are you doing a "getClass()" of a class in the .jar file? – paulsm4 Oct 29 '15 at 09:06 — paulsm4, Oct 29 '15 at 09:06

score 0 · Accepted Answer · edited May 23 '17 at 10:27

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From - In java, how do you retrieve images from a jar file?

It is indeed simple: you use the various getResource() methods in java.lang.Class and java.lang.ClassLoader. For example, in your app, you could just write

treeURL = getClass().getResource("/images/tree.png");

This would find the file in an images directory at the root of the jar file. The nice thing about the getResource() methods is that they work whether the files are in a jar or not -- if the images directory is a real directory on disk, this will still work (as long as the parent of images is part of your class path.)

edited May 23 '17 at 10:27

Community

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answered Oct 29 '15 at 09:10

Atul Kumar

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I've tried this code and still getting the same error. I have the following : URL treeURL = getClass().getResource("/masterImages/googleHomePage1.png"); Still getting a null pointer from within eclipse. Are there any oddities with windows file system that I need to be aware of? – Joseph Oct 29 '15 at 10:16
Interestingly, I just put a breakpoint on the line above, and when I check the contents of treeURL it is showing as null (so the null pointer is valid I would guess) - now to figure out why – Joseph Oct 29 '15 at 10:20

score 0 · Answer 2 · answered Oct 29 '15 at 10:55

Thanks to all. I think I have this sorted. Turns out I had to add the folder containing the image to the classpath - I wrongly assumed that as I had masterImages/otherFolderName that any file inside otherFolderName would be included if I included masterImages. Turns out this is not the case (at least for me.)

Referencing an image inside a jar file when running junit

2 Answers2