ResourceResolvers and Sessions — “you open it, you close it”

Update February 2023: Updated the list of API calls, which create a new Sling ResourceResolver (see this Forum thread). Thanks NitroHazeDev!

I have already written about how to use resource resolvers and JCR sessions; the basic pattern to remember is always “you open it; you close it” (2nd rule).

While this stanza seems to be quite commons sense, the question is always: When is a session or a resource resolver opened/created? What API calls are responsible for it? Let me outline this today.

API calls which open a JCR resource:

API calls, which create a Sling ResourceResolver

These are the only API calls which open a JCR Session or a Sling ResourceResolver. And whenever you use one of these, you are responsible to close them as well.

And as corollary to this rule: if you have other methods or APIs which return a ResourceResolver or Session: Do not close these.

Some examples:

Session jcrSession = resourceResolver.adaptTo(Session.clase);

This just exposes the internal JCR Session of the ResourceResolver and because it’s not using one of the above APIs: Do not close this session! It’s closed automatically when you close the resource resolver.

Session adminSession = slingRepository.loginAdministrative(null);
Map authInfo = new HashMap();
authInfo.put(, session);
ResourceResolver adminResourceResolver = resolverFactory.getResourceResolver(authInfo);

This code creates a resource resolver which wraps an already existing JCR Session. You have to close both adminSession and adminResourceResolver, because you created them both using the above mentioned API calls.