How to make IntelliJ IDEA insert a new line at every end of file?

Change your Editor settings:

Settings → Editor → General → Ensure line feed at file end on Save

For MAC users:

Preferences > Editor > General > Ensure line feed at file end on save

IntelliJ IDEA 2016.3

Approach 1

File > Settings... > Editor > General > Ensure line feed at file end on Save

https://i.stack.imgur.com/N6UIL.png

https://i.stack.imgur.com/TvtPj.png

Approach 2

Help > Find Action... (Ctrl+Shift+A) > type "Ensure line feed" > switch the toggle to ON (using the mouse click or Enter) for "Other: Ensure line feed at file end on Save" line

https://i.stack.imgur.com/9sLd8.png

https://i.stack.imgur.com/hpXIi.png

Possible alternative with a number of handy features is EditorConfig

Just submit an .editorconfig file to your repo

[*]
insert_final_newline = true

And it will work natively not only in Idea, but in all major IDEs (some require a plugin).

Now all team members would have same configuration, eol, eof, and no more tabs vs spaces :)

For Mac Users: IntelliJ Idea version 2020.2

Option1:

https://i.stack.imgur.com/zjGi1.png

Option2:

https://i.stack.imgur.com/eNS9Q.png

General -> Save Files For IntelliJ IDEA 2020.

https://i.stack.imgur.com/w3pP8.png

In latest versions of IntelliJ, the setting has been renamed to 'Ensure an empty line at the end of a file on save', and it has been moved under Setting>Editor>General>Save Files

https://i.stack.imgur.com/moYm4.png

This should have been a comment, but I wanted to add the screenshot as well so wrote as an answer.

As Rider (IDEA's cousin for .NET) is driving me crazy, this might be helpful for those writing C# as Ensure line feed at file end on Save alone won't work. It needs

File → Settings → Editor → Code Style → C# → Line Breaks and Wrapping → Line feed at end of file.

I don't remember changing it and I haven't imported any settings for sure, so I guess it's by default disabled.

https://i.stack.imgur.com/hvfgf.png

With the IntelliJ Idea version 2020.3: Go to File > Sttings > Editor > General > On Save

And then select/deselect "Ensure every saved file ends with a line break"

https://i.stack.imgur.com/FKkPm.png