Is this an Apache Poi bug in java? - apache-poi

Question

When I took out all the data in row #2, I noticed that my columns C, E, F were missing.
As follows:
My excel file is a new file, I only enter data for columns A, B, D, G, H and columns C, E, F. I don't touch (don't click or touch the cell)
image description
Then i use the following function to get the data from the columns of a row
Row row = sheet.getRow(i);
At this point, I noticed that the data of my columns C, E, F was lost. Specifically, in the row, only columns A, B, D, G, H and their respective data are displayed.
As the picture above, if I color the data row to white or any color or the columns C, E, F I click on (don't write data in the column). Then I re-read the file, now the row receives enough data from all columns A, B, C, D, E, F, G, H. with columns C, E, F, the data is empty.
What do I do when sheet.getRow() doesn't lose columns.

Answer 1

In a Excel sheet only those rows and cells that not are completely unused are stored. A row is stored if at least one cell needs to be stored in that row. A cell needs to be stored if it has a cell value or has a special cell style (using data formatting, font formatting, interior formatting...). All other possible rows and/or cells are not stored.
So what you observed is not a bug in Apache POI but shows how Excel uses it's storage for rows and cells in sheets. Storing all possible cells would be a horrible waste of storage.
For not stored rows, Sheet.getRow return null. For not stored cells, Row.getCell return null. Not stored rows as well as not stored cells are not reachable using iterators.
So, if the need is to iterate over cells, with control of missing / blank cells, then the iterators are not usable. See Iterate over rows and cells -> Iterate over cells, with control of missing / blank cells.
Sample code provided there:
// Decide which rows to process
int rowStart = Math.min(15, sheet.getFirstRowNum());
int rowEnd = Math.max(1400, sheet.getLastRowNum());
for (int rowNum = rowStart; rowNum < rowEnd; rowNum++) {
Row r = sheet.getRow(rowNum);
if (r == null) {
// This whole row is empty
// Handle it as needed
continue;
}
int lastColumn = Math.max(r.getLastCellNum(), MY_MINIMUM_COLUMN_COUNT);
for (int cn = 0; cn < lastColumn; cn++) {
Cell c = r.getCell(cn, Row.RETURN_BLANK_AS_NULL);
if (c == null) {
// The spreadsheet is empty in this cell
} else {
// Do something useful with the cell's contents
}
}
}
As you see, you need to know needed first row and needed last row as well as needed column count. The sample code always starts om column 0 (A). Maybe you also know the first needed column to start there. And you need to null-check the row as well as the cell you got.