public Collection<ActiveConnectionRecord> get(String identifier) {
        synchronized (records) {

            // Get set of active connection records
            Collection<ActiveConnectionRecord> connections = records.get(identifier);
            if (connections != null)
                return Collections.unmodifiableCollection(connections);

            return Collections.<ActiveConnectionRecord>emptyList();

        }
    }
Returns a collection of active connection records associated with the
object having the given identifier. The collection will be sorted in
insertion order. If there are no such connections, an empty collection is
returned.

@param identifier
    The identifier of the object to check.

@return
    An immutable collection of records associated with the object having
    the given identifier, or an empty collection if there are no such
    records.
extensions/guacamole-auth-jdbc/modules/guacamole-auth-jdbc-base/src/main/java/org/apache/guacamole/auth/jdbc/tunnel/ActiveConnectionMultimap.java