Apply various code quality fixes, remove unused imports, use diamond operator, try-with-resources, etc

[hansenmc]

• remove unused imports
• use try-with-resources for closeable objects
• use diamond operator for object construction
• use addAll() instead of iterating over every item and adding each one
• use Map.computeIfAbsent() to simplify
• use StringBuilder instead of concatenating strings inside of a loop
• use equalsIgnoreCase when comparing values without caring about case