why I can't compile successfully with the following code?

Question

public class PoiSheetUtil{
    public Workbook mergeExcelFiles(Workbook book, Map<Integer,InputStream> inMap) throws IOException, 
    InvalidFormatException{
        inMap.forEach((k,v)->{
            Workbook b = WorkbookFactory.create(v);
           //omit copy sheet method
            copySheets(book.createSheet(),b.getSheetAt(k));
        });
        return book;
    }
}

I get an error on line 5 which say that "Unhandled exception IOException,InvalidFormatException"

IOException and InvalidFormatException are checked exceptions so you need to catch them and handle them somewhere(for example you can catch them in the the method that calls your method mergeExcelFiles() ) — VFX, Oct 24 '20 at 08:48

score 2 · Accepted Answer · answered Oct 24 '20 at 08:49

The problem here is context; the code that potentially throws the exception sits in the lambda:

inMap.forEach((k,v)->{
    Workbook b = WorkbookFactory.create(v);
    ...
});

and it's the lambda expression, that does not properly handle the exceptions in this case. Try

inMap.forEach((k,v)->{
    try {
        Workbook b = WorkbookFactory.create(v);
        ...
     } catch (IOException | InvalidFormatException exc) {
         throw new RuntimeException(exc);
     }
  });

or use some other kind of iteration construct (e.g., an iterator based for statement) which can propagate the exception transparently:

for (var entry: inMap.entrySet()) {
     final var k = entry.getKey();
     final var v = entry.getValue();
     ...
}

why I can't compile successfully with the following code?

1 Answers1