Safety-critical Java (SCJ) is designed to enable development of applications that are amenable to certification under safety-critical standards. However, its shared-memory concurrency model causes several problems such as data races, deadlocks, and priority inversion. We propose therefore a dataflow design model of SCJ applications in which periodic and aperiodic tasks communicate only through lock- free channels. We provide the necessary tools that compute scheduling parameters of tasks (i.e. periods, phases, priorities, etc) so that uniprocessor/multiprocessor preemptive fixed-priority schedulability is ensured and the throughput is maximized. Furthermore, the resulted schedule together with the computed channel sizes ensure underflow/overflow- free communications. The scheduling approach consists in constructing an abstract affine schedule of the dataflow graph and then concretizing it.