We currently don't have a mechanism in gatein to handles things like JBoss Portal used to do with those xml files.
There is a way to extend a portal, and within that extension you can add things like an extra page and add portlets to it (see the gatein-sample-extension.ear for an example of how it works). But this has some limitation like it needs to exist when the portal is first started (ie with a clean data directory), you can't just deploy it at anytime and expect it to work. So its not really a replacement for the object and instances xml files.
I don't know if we have plans to add this feature in the future
are there news??
How can I develope a custom site in gatein with stage environment and production environment?
1) create a portal extension
2) made some change
3) then?? How can redeploy the extension or export the changes from one environment to another?
Whit this tool (http://community.jboss.org/wiki/GateIn-ExportImpor) is possible to merge the stage env with the production env? Pages, navigations, portal xml are ok, but data already saved on production/stage env?
The tool will only overwrite data that exists in both environments (unless you specify the "overwrite" feature of the tool, which will delete anything not in the export). In other words it will add things that doesn't exist or overwrite data that exists in both. There are plans to support more scenarios like "if exists keep" as in the previous jboss portal and the ability to deploy these updates via war/ear file.
Also the CLI tool allows you to export/import individual pages and navigation nodes. So if you are worried about exporting/importing everything, you can choose which "portal objects" you want to export/import.