Fix Java project structure.

src/fs.rs

@@ -10,7 +10,12 @@ pub fn expand_files<P: AsRef<Path>>(path: P) -> anyhow::Result<Vec<PathBuf>> {
     Ok(std::fs::read_dir(path)?
         .filter_map(|entry| {
             let path = entry.ok()?.path();
-            if path.is_file() { Some(path) } else { None }
+            if path.is_dir() {
+                Some(expand_files(path).ok()?)
+            } else {
+                Some(vec![path])
+            }
         })
+        .flatten()
         .collect())
 }