Java is becoming a viable platform for hard real-time computing. There are production and research real-time Java VMs, as well as applications in both military and civil sector. Technological advances and increased adoption of Real-time Java contrast significantly with the lack of real-time benchmarks. The few benchmarks that exist are either low-level synthetic micro-benchmarks, or benchmarks used internally by companies, making it difficult to independently verify and repeat reported results. This paper presents the CDx (Collision Detector) benchmark suite, an open source application benchmark suite that targets different hard and soft real-time virtual machines. CDx is, at its core, a real-time benchmark with a single periodic task, which implements aircraft collision detection based on simulated radar frames. The benchmark can be configured to use different sets of real-time features and comes with a number of workloads. We describe the architecture of the benchmark and characterize the workload based on input parameters.v