1. 添加依赖

        <dependency>
            <groupId>commons-io</groupId>
            <artifactId>commons-io</artifactId>
            <version>2.6</version>
        </dependency>

2. 使用

此处获取C盘Tools文件夹大小

    public void getSize() {
        long size = FileUtils.sizeOfDirectory(new File("C:/Tools"));
        System.out.println("Size: " + size + " bytes");

    }