The modular analysis of control flow of incompleteJava bytecode programs is challenging, mainly because of the complex semantics of the language,and the unknown inter-dependencies between the available and unavailable components.In this paper we describe a technique for incremental, modular extraction ofcontrol flow graphs that are provably sound w.r.t.~sequences of method invocations and exceptions.The extracted models are suitable for various program analyses,in particular model-checking of temporal control flow safety properties.Soundness comes at the price of over-approximation,potentially giving rise to false positives reports during verification.Still, our technique supports incremental refinement of the already extracted models,as more components code becomes available.The extraction has been implemented as the ConFlex tool, and test-cases show its utility and efficiency.