IntelliJ: Working on multiple projects
Yes, your intuition was good. You shouldn't use three instances of intellij. You can open one Project and add other 'parts' of application as Modules. Add them via project browser, default hotkey is alt+1
I think this has improved with recent versions of IntelliJ. In my current version (12.0.2), you can add any number of separate Maven projects to the same "workspace".
The simplest way I've found to do this is to click the little +
icon in the "Maven Projects" window (View > Tool Windows > Maven Projects) and then select the additional pom file you want to import.
Prequisite
Having all the related projects in the same root directory can be helpful.
Steps
1) First you create a new Empty project
2) Then you select the root directory of all your projects.
This will create a empty project, with a .idea directory that will simply remember the module organisation we are about to do in the next step
3) Then, in the next window, you import the different projects as modules
4) In the next window, to import each project, simply double click on the build.gradle, or pom.xml
The project will be imported as a new module.
5) Done, you now have all your projects as modules, opened on the same IntelliJ project
Step 1: open "Maven Projects"
Step 2: select the project you want to import: