private FileTree excludeOutputDirectory(FileTree sourceTree) { if (sourceTree == null) { return null; } Spec<File> outputDirectoryFilter = new Spec<File>() { @Override public boolean isSatisfiedBy(File file) { return file.getAbsolutePath().contains(getOutputDirectory().getAbsolutePath()); } }; sourceTree = sourceTree.minus(sourceTree.filter(outputDirectoryFilter)).getAsFileTree(); return sourceTree; }