Code quality improvement and codebase optimization

[BenCheung0422]

For various reasons, the code quality should be improved, including formats, coding practices and error handlings. This includes making good use of standard libraries like Google Guava, Apache Commons, etc., reducing unnecessary blocks of codes and optimizing the codebase. The JavaDoc commenting style should also be united, an example can be taken from #579. Ideally, any potential errors and exceptions should be caught and handled properly, minimizing the chances getting unhandled errors, uninformative reports and unideal fallbacks/case handlings, thus making it cooperative with the upcoming crash report system (#461). This may need time to be come over.