Coverage-Based Debloating for Java Bytecode

Software bloat is code that is packaged in an application but is actually not necessary to run the application. The presence of software bloat is an issue for security, for performance, and for maintenance. In this paper, we introduce a novel technique for debloating Java bytecode, which we call coverage-based debloating. We leverage a combination of state-of-the-art Java bytecode coverage tools to precisely capture what parts of a project and its dependencies are used at runtime. Then, we automatically remove the parts that are not covered to generate a debloated version of the compiled project. We successfully generate debloated versions of 220 open-source Java libraries, which are syntactically correct and preserve their original behavior according to the workload. Our results indicate that 68.3% of the libraries' bytecode and 20.5% of their total dependencies can be removed through coverage-based debloating. Meanwhile, we present the first experiment that assesses the utility of debloated libraries with respect to client applications that reuse them. We show that 80.9% of the clients with at least one test that uses the library successfully compile and pass their test suite when the original library is replaced by its debloated version.