For a Java developer it is really like heaven, with a vast helpful Java Components, Apache is making a developers life much easier. Check out this Apache commons home page http://commons.apache.org/ there are so many components and all available under Apache License. Being a Java Developer i myself have used a lot of them. Following are some of the ones i have used:
Commons IO – FileUtils has many helper methods like copyStringtoFile, copyDirectory, touch.. etc
Commons DBCP – Enables connection pooling to interact with any relational database.
Commons Email – Provides easy to use classes and methods for sending emails through any Java application.
Commons FileUpload – Adds file upload functionality to a Java web application.
Commons Net – Ftp Client classes and methods helps in connecting to a ftp server and transfer or do any other operations on a ftp server.
Commons Logging – Provides classes and methods for logging in any Java application.
Commons Sanselan – Java image library
Commons Lang – Provides some utility classes like DateUtils for easy working with Dates.
Commons Digestor – Classes and methods which can be used for parsing XML to java objects.
and lots more… Thank you Apache Commons!