在Excel中动态更改单元格颜色

Question

I'm using POI library to deal with the Excel file, I want to change the ForGroundColor of the particular cells. As I'm not satisfied with the list of IndexedColors I want to create my own by substituting one already existing (in my case HSSFColor.BLUE), the problem is - it saves only the color from the last iteration (all cells have the same color).

The code (convData - two dim double array, normalized to 255):

     HSSFPalette hssfPalette = excelFile.getCustomPalette();
        CellStyle cellStyle = excelFile.createCellStyle();
        hssfPalette = excelFile.getCustomPalette();
        cellStyle.setFillPattern(CellStyle.SOLID_FOREGROUND);

        for (int i=0; i<convData.length; i++) {
            Row row = excelSheet.createRow(i);
            for (int j=0; j<convData[i].length; j++) {
                Cell cell = row.createCell(j);

                hssfPalette.setColorAtIndex(HSSFColor.BLUE.index, convData[i][j].byteValue(), convData[i][j].byteValue(), convData[i][j].byteValue());
                cellStyle.setFillForegroundColor(hssfPalette.getColor(HSSFColor.BLUE.index).getIndex());
                cell.setCellStyle(cellStyle);
            }
        }

Answer 1

Your problem is that you're creating one single cell style, assigning it to a bunch of cells, then changing it to be blue part way through. As the cell style is global, that blue then applies to everything

Instead, you either need move the "redefine what blue is" outside of the loop, or create a new cell style + apply colour to it for each differently coloured cell. However, there's a limit to the number of colours and cell styles you can have, so make sure you re-use them if you have multiple cells wanting the same colour