FileUtils功能概述

https://commons.apache.org/proper/commons-io/javadocs/api-release/org/apache/commons/io/FileUtils.html

General file manipulation utilities.

Facilities are provided in the following areas:

• writing to a file
• reading from a file
• make a directory including parent directories
• copying files and directories
• deleting files and directories
• converting to and from a URL
• listing files and directories by filter and extension
• comparing file content
• file last changed date
• calculating a checksum

converting to and from a URL，要是自己实现，太浪费绳命了。写Java，就得熟悉Apache Common和Google Guava，省了不知道多少劲呢！