Ant buildfiles are just text files, so the most straightforward way to create an Ant buildfile in Eclipse is:
By default the Ant editor only has an association with build.xml named files. As the user you can designate for the Ant editor to be considered for all xml files.
Now, as long as the file has a .xml extension, Eclipse will consider it to be a possible Ant buildfile, and will enable Ant-related actions when it is selected. Until a file has Ant buildfile content, you will need to open it using Open With > Ant Editor.
As will be demonstrated in a later section, an Ant buildfile can be created for an Eclipse plug-in that contains predefined targets that are useful for deploying the plug-in.