Currently, the blob store interface exposes an inDirectory() method to set the directory from which to list blobs. This is implemented through a combination of prefix and delimiter options, namely combining them to retrieve all objects nested under a specific "directory" (e.g. dir/).
jclouds should expose an explicit prefix option to, for example, allow listing objects that all start with a common name. The difference from the existing inDirectory() option is that the prefix would not require the delimiter to be set and could be an arbitrary string.
The prefix is an option supported by S3, Swift, Azure, and Google Cloud Storage.