I am trying to create a plugin that loads different resources taken from the loaded project. I am trying to register to ResourceChangeListener of the workspace in an early stage
If you want to know the resources (i.e. projects) that are open in a workspace, you can just get the IWorkspace and look at the project contained in it.
IWorkspace workspace = ResourcesPlugin.getWorkspace();
IWorkspaceRoot rootResource = workspace.getRoot();
Then you should be able to just traverse this tree structure to find out about all the resources. Hope this helps.
Here are some resources: