Dependency Injection (DI) is a commonly applied mechanism to decouple classes from their dependencies in order to provide higher modularization. However, bad DI practices often lead to negative consequences, such as increasing coupling. Although white literature conjectures about the existence of DI anti-patterns, there is no evidence on their practical relevance, usefulness, and generality. The objective of this study is to propose and evaluate a catalog of DI anti-patterns and associated refactorings. We reviewed existing reported DI anti-patterns in order to analyze their completeness. The limitations found in literature motivated proposing a novel catalog of 12 DI anti-patterns. We developed a tool to statically analyze the occurrence level of the candidate DI anti-patterns in both open-source and industry projects. Next, we survey practitioners to assess their perception on the relevance, usefulness, and their willingness on refactoring anti-pattern instances of the catalog. Our static code analyzer tool showed a relative recall of 92.19% and high average precision. It revealed that at least 9 different DI anti-patterns appeared frequently in the analyzed projects. Besides, our survey confirmed the perceived relevance of the catalog and developers expressed their willingness to refactor instances of anti-patterns from source code. The catalog contains DI anti-patterns that occur in practice and that are perceived as useful. Sharing it with practitioners may help them to avoid such anti-patterns, thus improving source-code quality.

Background: Unhandled exceptions affect the reliability of web applications. Several studies have measured the reliability of web applications in use against unhandled exceptions, showing a recurrence of the problem during the maintenance phase. Detecting latent unhandled exceptions automatically is difficult and application-specific. Hence, general approaches to deal with defects in web applications do not treat unhandled exceptions appropriately. Aims: To design and evaluate a method that can support finding, correcting, and preventing unhandled exceptions in web applications. Method: We applied the design science engineering cycle to design a method called Pattern-Driven Maintenance (PDM). PDM relies on identifying defect patterns based on application server logs and producing static analysis rules that can be used for prevention. We applied PDM to two industrial web applications involving different companies and technologies, measuring the reliability improvement and the precision of the produced static analysis rules. Results: In both cases, our approach allowed identifying defect patterns and finding latent unhandled exceptions to be fixed in the source code, enabling to completely eliminate the pattern-related failures and improving the application reliability. The static analysis rules produced by PDM achieved a precision of 59-68% in the first application and 89-100% in the second, where lessons learnt from the first evaluation were addressed. Conclusions: The results strengthen our confidence that PDM can help maintainers to improve the reliability for unhandled exceptions in other existing web applications.