Basically, in the book there is that "classpath:" in the front of the file name. That tells Spring to look in the classpath for the file. But without any pathing after classpath: means that it will look for that file only in the root of the classpath. So you have to tell Spring from the root of the classpath, what is the path to the file.
In your case you are using
Maven, so anything in the src/main/resources/ directory will be copied to the root of the classpath.
so
src/main/resources/mark.txt copied to the root of the classpath
src/main/resources/something/anotherDir/myfile.txt is copied to
/something/anotherDir/myfile.txt off the root of the classpath.
Mark