Refactoring: misc part 1

For easier code reading the following refactoring can be done:
- Boolean constructor call (replace with Boolean.valueOf())
- Bulk operation can be used instead of iteration (replace with addAll())
- Call to 'Arrays.asList()' with too few arguments (replace with Collections.singletonList())
- 'Collection.toArray()' call style (replace argument with empty array)
- 'addAll()' call can be replaced with parametrized constructor call
- C-style array declaration (replace with Java style)
- Standard Charset object can be used ("UTF8" to be replaced with StandardCharsets.UTF_8)
- Unnecessary 'String.valueOf()' call