How to reference a resource file correctly for JAR and Debugging?

I have a nasty problem referencing resources when using a Maven project and Jar files...

I have all my resources in a dedicated folder /src/main/resources which is part of the build path in Eclipse. Files are referenced using

getClass().getResource("/filename.txt")

This works fine in Eclipse but fails in the Jar file - there the resources are located in a folder directly below the jar's root...

Does anyone know a 'best practice' to reference a file both in the JAR and (!) in Eclipse?

Edit: The problem is that while the resources actually are located in the JAR in a folder "resources" at the top level, the above method fails to find the file...

Once you pack the JAR, your resource files are not files any more, but stream, so getResource will not work!

Use getResourceAsStream.

To get the "file" content, use https://commons.apache.org/proper/commons-io/javadocs/api-release/org/apache/commons/io/IOUtils.html:

static public String getFile(String fileName)
{
        //Get file from resources folder
        ClassLoader classLoader = (new A_CLASS()).getClass().getClassLoader();

        InputStream stream = classLoader.getResourceAsStream(fileName);

        try
        {
            if (stream == null)
            {
                throw new Exception("Cannot find file " + fileName);
            }

            return IOUtils.toString(stream);
        }
        catch (Exception e) {
            e.printStackTrace();

            System.exit(1);
        }

        return null;
}

I had a similar problem. After a full day of trying every combination and debugging I tried getClass().getResourceAsStream("resources/filename.txt") and got it to work finally. Nothing else helped.

The contents of Maven resource folders are copied to target/classes and from there to the root of the resulting Jar file. That is the expected behaviour.

What I don't understand is what the problem is in your scenario. Referencing a Resource through getClass().getResource("/filename.txt") starts at the root of the classpath, whether that (or an element of it) is target/classes or the JAR's root. The only possible error I see is that you are using the wrong ClassLoader.

Make sure that the class that uses the resource is in the same artifact (JAR) as the resource and do ThatClass.class.getResource("/path/with/slash") or ThatClass.class.getClassLoader().getResource("path/without/slash").

But apart from that: if it isn't working, you are probably doing something wrong somewhere in the build process. Can you verify that the resource is in the JAR?

If you add the resources directory in the jar file (so it is under the /resources folder in the jar, and if /src/main is in your build path in eclipse, then you should be able to reference your file as:

getClass().getResource("/resources/filename.txt");  

Which should work in both environments.

The problem is that within the IDE the getClass().getResource("Path"); String is not CASE SENSITIVE when accessing a file but when running from a jar it is. Check your Capitalisation on directory compared to file. It does work. Also if you try new File(getClass().getResource("Path"); the file won't be readable outside IDE.

Maybe this method can help for some situations.

public static File getResourceFile(String relativePath)
{
	File file = null;
	URL location = <Class>.class.getProtectionDomain().getCodeSource().getLocation();
	String codeLocation = location.toString();
	try{
		if (codeLocation.endsWith(".jar"){
			//Call from jar
			Path path = Paths.get(location.toURI()).resolve("../classes/" + relativePath).normalize();
			file = path.toFile();
		}else{
			//Call from IDE
			file = new File(<Class>.class.getClassLoader().getResource(relativePath).getPath());
		}
	}catch(URISyntaxException ex){
		ex.printStackTrace();
	}
	return file;
}

Just copy the file to a temporary directory.

String tempDir = System.getProperty("java.io.tmpdir");
File file = new File(tempDir.getAbsolutePath(), "filename.txt");
if (!file.exists()) {
     InputStream is = (getClass().getResourceAsStream("/filename.txt"));
     Files.copy(is, file.getAbsoluteFile().toPath());
}