When is a .project/.classpath created for a Java project? What determines a project nature?

[tsiyona]

Background:

• I am writing an Eclipse plugin to run with Theia. The purpose of this plugin is to query the workspace, recognize its content (projects), report the groupId:artifactId:version of Maven projects, provide a fully-qualified-class-name for a given java source file, provide the full path for a given fully-qualified-java-class, etc.

• For this purpose, I need Theia (ResourcePlugin, in fact) to recognize the projects in the workspace, so I can use JDT APIs to obtain the information I need.

• I noticed that folders containing a '.project' descriptor file are recognized by ResourcePlugin as projects in the workspace.

• I assume the addition of the .project/.classpath files is performed by m2e and/or buildship (for Maven and Gradle respectively).

Scenario #1:

I have a workspace which contains two java projects. Each of these projects has its own pom.xml file.
When I open the workspace in Theia, the project is silently added '.project' and '.classpath' files, and is marked (in .project file) as having a Java nature and a Maven nature.
The second project is marked only with a Maven nature, and silently gets a '.project' file only (no '.classpath' file).
ResourcesPlugin will recognize the first project as a Java+Maven project, and the second project as a Maven project.

Scenario #2:

I have a workspace which contains two projects. The first project has a 'build.gradle' file. The second project has a pom.xml file.
When I open this workspace in Theia, the gradle project is silently added a '.project' file and is marked as a Gradle project.
The second project is not added a '.project' file at all.
ResourcesPlugin will identify the gradle project only, and the second project will not be listed as a project in the workspace.

Can someone please explain why the behavior described in the two scenarios above occurs?