You can add resources in both main and test in your project. Add a text file in src/main/resources. Then you can access that via
Reader ios = new InputStreamReader(getClass().getClassLoader().getResourceAsStream("file.txt"));
String s = IOUtils.toString(ios);
This is because the file.txt will be in target/classes/ now
In your test directory, you can put different resources there. A file in src/test/resources/ can be accessed via similar methods, but this time in the test java files.
You can also filter these resource files. That is, define a filter, which is a key value type file, which will be used to replace values in the resource file. Here's the default.properties in src/main/filters
Here's a test.xml in src/main/resources
Now in our POM we need to define that the xml will be filtered