How do I create custom instance templates in IntelliJ IDEA?

Intellij supports 'instance templates' i.e. templates usable with expression followed by a period, such as cast, new etc. So MyClass.new expands to new MyClass(I) where I is the cursor.

Now I want to create my own template, expression.orElse which expands to:

Optional.ofNullable(expression).orElse(I)

I tried looking for options in Editor > Live Templates, but couldn't find anything relevant. Is this not possible in IntelliJ IDEA, or am I missing something?

Solution

These 'instance templates' are actually called postfix completion templates in IDEA.

Starting with version 2019.2, custom postfix templates can also be created by going to Editor > General > Postfix Completion, as specified here and detailed in this blog post.

For the asked case, the values would be:

Key: orElse
Minimum language leve: 8
Applicable expression types: non void

Value:

Optional.ofNullable($EXPR$).orElse($END$)

Variables:

$EXPR$ : Replaced by the target expression
$END$ : Location of cursor after substitution

Enabling 'Apply to the topmost expression' disables the scope selection popup that appears on selecting the template.