Hutool 3.9 File

Hutool 3.0.9 (likely what you mean by 3.9) is a foundational version of the popular Java tool library. It focuses on reducing boilerplate code by providing a comprehensive suite of static utility methods. Core Strengths of Hutool 3.x

Zero Dependencies: It is designed to be lightweight, avoiding "jar hell" by not forcing other libraries into your project.

Swiss Army Knife Approach: It covers everything from basic string manipulation to complex file I/O and encryption.

Static Utilities: Most functions are accessed via simple static calls (e.g., DateUtil.now()), making your code highly readable. Key Modules in this Version

Core: Handles basic tasks like StrUtil (string handling), ClassUtil (reflection), and ArrayUtil. Hutool 3.9

DateUtil: Simplifies the notoriously clunky Java date/time API.

IoUtil & FileUtil: Streamlines reading, writing, and copying files or streams.

HttpUtil: A simple, functional HTTP client for sending GET and POST requests.

CryptoUtil: Easy-to-use wrappers for MD5, SHA, AES, and DES encryption. JsonUtil: Basic JSON parsing and generation. Maven Dependency If you are using Maven, add this to your pom.xml: Hutool 3

com.xiaoleilu hutool-all 3.0.9 Use code with caution. Copied to clipboard

(Note: Version 3.x used the com.xiaoleilu group ID; modern versions 4.x+ use cn.hutool.)

Note: Hutool 3.9.x was released circa late 2018 – early 2019. The current major version is 5.x/6.x. This report focuses on features introduced and stabilized in the 3.9 branch.

Usage Example:

// Watch multiple patterns with different handlers
FileWatcherPro.of(Paths.get("/logs"))
    .onFiles("*.log", (path, event) -> 
        // Auto-rotate logs on modification
        LogRotator.rotateIfNeeded(path);
    )
    .onFiles("*.tmp", (path, event) -> 
        // Auto-delete temp files after 1 hour
        FileUtil.del(path);
    )
    .on(Paths.get("config.yml"), ENTRY_MODIFY, ENTRY_DELETE)
    .start(); // Runs on virtual thread

Conclusion: Why You Should Add Hutool 3.9 to Your Project Today

Java is verbose by design. But that doesn’t mean your code has to be. Hutool 3.9 sits silently in your classpath, saving you thousands of if statements, null checks, and 5-line file read routines. It is the duct tape and WD-40 of Java development. Note: Hutool 3

Whether you are processing collections, scraping HTTP endpoints with HttpUtil, generating QR codes (yes, 3.9 supports basic QR via QrCodeUtil), or just formatting dates – Hutool 3.9 makes Java feel like a modern, high-level language.

Stop writing boilerplate. Start using Hutool 3.9.

1. Overview

Hutool is a lightweight, well-structured Java utility library that reduces boilerplate code.
Version 3.9 represents a mature release in the 3.x series, focusing on: