Creating Ant buildfiles

Ant buildfiles are just text files, so the most straightforward way to create an Ant buildfile in Eclipse is:

File > New > File.
Enter a name for the file.
Click Finish.

By default the Ant editor only has an association with build.xml named files. As the user you can designate the Ant editor to be considered for all xml files.

File associations can be set using the Window > Preferences > General > Editors >File Associations
Add an association between *.xml and the Ant editor.

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.

An example is the use of project builders, where an Ant buildfile is created for an Eclipse plug-in that contains predefined targets that are useful for deploying the plug-in.