Use try-with-resources to prevent potential resource leaks

* Detected by enabling all resource-related Java compiler warnings
 * Java -> Compiler -> Errors/Warnings
 * Filtering for "resource" should show 3 warnings
 * Set to "Warning"

Issue-Ref: 3539
Issue-Url: https://af3-developer.fortiss.org/issues/3539



Signed-off-by: Simon Barner <barner@fortiss.org>