To create ear file for maven spring boot multi-module project I have created separate package with packaging type ear and after that I added dependency of other modules to this ear module so that my project structure is like below.
Parent Project (Packaging type : POM)
-First Child module(web Project and Packaging type : war)
-Second Child module(Packaging type : war)
-Third Child module(Packaging type : jar)
-fourth child module(Packaging type : ear)
where in fourth child module I have added dependency of first three modules and deployed this ear file on Enterprise Application Server like JBoss etc.