Affects Version/s: 5.9.0
Fix Version/s: 5.10.0
Steps to reproduce
1. import and export any file
2. monitor the keikai web application with VisualVM
3. performant GC and get a heap dump on the server, search XSSFWorkbook
JVM garbage collector doesn't clear Workbook because it's referenced by an Exporter.
Since XSSFWorkbook consumes lots of memory, if many users perform exporting, many referenced Workbook will consume a lot of memory.
JVM garbage collector can clear Workbook
check if there are other variables that need to be nullified for the same reason