public String getFileContents(String fileName) {
...
}

public class FileSystemUtils {

	public void generateFileIfNotExists(IFileSystemAccess fsa, String fileName,
			CharSequence contents) {
		File tFile = new File(getBasePath(fsa).getAbsolutePath()
				+ File.separator + fileName.substring(3));

		if (!tFile.exists()) {
			fsa.generateFile(fileName, contents);
		}
	}

	public File getBasePath(IFileSystemAccess fsa) {

		try {
			Field rootField = fsa.getClass().getDeclaredField("root");
			rootField.setAccessible(true);
			Object rootObject = rootField.get(fsa);

			Method folderMethod = rootObject.getClass().getMethod("getFolder",
					String.class);
			Object folder = folderMethod.invoke(rootObject, getProjectName(fsa)
					+ File.separator + "tmp");

			URI locationURI = (URI) folder.getClass()
					.getMethod("getLocationURI").invoke(folder);
			String tPath = locationURI.getPath();

			File basePath = new File(tPath);

			return basePath.getParentFile();

		} catch (Exception e) {
			throw new RuntimeException(e);
		}
	}

	public String getProjectName(IFileSystemAccess fsa) {

		try {
			Field pathesField = AbstractFileSystemAccess.class
					.getDeclaredField("pathes");
			pathesField.setAccessible(true);
			@SuppressWarnings("unchecked")
			Map<String, String> pathes = (Map<String, String>) pathesField
					.get(fsa);
			return pathes.get(IFileSystemAccess.DEFAULT_OUTPUT).split(
					File.separator)[1];
		} catch (Exception e) {
			throw new RuntimeException(e);
		}

	}

}

@Inject extension FileSystemUtils fsu
	
	def doGenerate(Entity entity, IFileSystemAccess fsa){
		
		var basePath = fsa.basePath;
		
		fsa.generateFileIfNotExists("myProject/" + entity.name + ".h", entity.compileHeader)