The 3.x branch (including 3.9) laid the groundwork for the modern library's philosophy of being "sweet"—making Java as elegant as a functional language. It primarily improved stability in its JDBC (hutool-db) and Excel (hutool-poi) handling.
// Hutool 3.9 approach FileUtil.copy(source, dest, true); Hutool 3.9
// Reads all lines from a UTF-8 file. Auto-closes. List<String> lines = FileUtil.readLines("config/users.txt", "UTF-8"); lines = FileUtil.readLines("config/users.txt"