this.getClass().getClassLoader().getResource("...") and NullPointerException

Solution 1:

When you use

this.getClass().getResource("myFile.ext")

getResource will try to find the resource relative to the package. If you use:

this.getClass().getResource("/myFile.ext")

getResource will treat it as an absolute path and simply call the classloader like you would have if you'd done.

this.getClass().getClassLoader().getResource("myFile.ext")

The reason you can't use a leading / in the ClassLoader path is because all ClassLoader paths are absolute and so / is not a valid first character in the path.

Solution 2:

tul,

• When you use .getClass().getResource(fileName) it considers the location of the fileName is the same location of the of the calling class.
• When you use .getClass().getClassLoader().getResource(fileName) it considers the location of the fileName is the root - in other words bin folder.

Source :

package Sound;
public class ResourceTest {
    public static void main(String[] args) {
        String fileName = "Kalimba.mp3";
        System.out.println(fileName);
        System.out.println(new ResourceTest().getClass().getResource(fileName));
        System.out.println(new ResourceTest().getClass().getClassLoader().getResource(fileName));
    }
}

Output :

Kalimba.mp3
file:/C:/Users/User/Workspaces/MyEclipse%208.5/JMplayer/bin/Sound/Kalimba.mp3
file:/C:/Users/User/Workspaces/MyEclipse%208.5/JMplayer/bin/Kalimba.mp3

Solution 3:

It should be getResource("/install.xml");

The resource names are relative to where the getClass() class resides, e.g. if your test is org/example/foo/MyTest.class then getResource("install.xml") will look in org/example/foo/install.xml.

If your install.xml is in src/test/resources, it's in the root of the classpath, hence you need to prepend the resource name with /.

Also, if it works only sometimes, then it might be because Eclipse has cleaned the output directory (e.g. target/test-classes) and the resource is simply missing from the runtime classpath. Verify that using the Navigator view of Eclipse instead of the Package explorer. If the files is missing, run the mvn package goal.

Solution 4:

I had the same issue with the following conditions:

• The resource files are in the same package as the java source files, in the java source folder (src/test/java).
• I build the project with maven on the command line and the build failed on the tests with the NullPointerException.
• The command line build did not copy the resource files to the test-classes folder, which explained the build failure.
• When going to eclipse after the command line build and rerun the tests in eclipse I also got the NullPointerException in eclipse.
• When I cleaned the project (deleted the content of the target folder) and rebuild the project in Eclipse the test did run correctly. This explains why it runs when you start with a clean project.

I fixed this by placing the resource files in the resources folder in test: src/test/resources using the same package structure as the source class.

BTW I used getClass().getResource(...)