Optional Ant Tasks

Optional tasks are bundled with Ant and depend on libraries that do not belong to the Ant project (core tasks have no such dependences), and they come bundled as part of the Ant distribution, as do the libraries, so you can still use them in your projects. If the tasks that come bundled with Ant do not give you the options you want, you have two choices. First, you can use Ant to run a command-line tool if one exists that does what you want to do. Second, you can write your own task, which simply means you would write a Java class that implements the desired behavior. You can then use this custom task in future projects and distribute it.
Writing a custom task has the same advantages that Ant has over other build tools in that your new task can go wherever Ant can. If your project demanded a step that was possible only at the command line on Windows, then you could not build it on Unix unless you wrote a custom task. Java and Ant are portable; Windows tools are not necessarily so.