java,excel,apache-poi , Cannot create new excel sheet in a workbook using apache POI


Cannot create new excel sheet in a workbook using apache POI

Question:

Tag: java,excel,apache-poi

I am trying to copy multiple files in a singe excel file. Each sheet in that excel file will carry contents of one file. And there are around 6 files that I need to copy. So the resultant file should contain 6 sheets. But when I run my code only 1 sheet is generated for a single file. I tried debugging it but could not figure out the reason.

This is my code.

 public static void main(String[] args) throws IOException {

    // TODO Auto-generated method stub
    CreateSingleExcelFile cef = new CreateSingleExcelFile();
    cef.fileIterator();
 }

 public void fileIterator() throws IOException{

    File dir = new File("path for files to copy");
    File[] dir_listing = dir.listFiles();
    HSSFWorkbook my_wb = new HSSFWorkbook();                        
    //creating an output stream to copy all files in combined.xls
    BufferedOutputStream bos= new BufferedOutputStream(new FileOutputStream("path of resultant excel sheet"));
    //traversing through a list of files
    for(File file: dir_listing){
        //file: file to be copied.
        add_in_excel(my_wb,bos,file);
        System.out.println("In file :" + file.getName());
    }
    bos.close();
    System.out.println("Files are copied");
}


 private void add_in_excel(HSSFWorkbook copy_wb, BufferedOutputStream bos,File file) throws IOException {
    // TODO Auto-generated method stub
    //creating a new sheet in the copy workbook
    HSSFSheet mySheet =  copy_wb.createSheet(file.getName());

    BufferedInputStream bis = new BufferedInputStream(new FileInputStream(file));
    HSSFWorkbook workbook = new HSSFWorkbook(bis);
    CellStyle cs = copy_wb.createCellStyle();
    cs.setWrapText(true);   

    HSSFSheet sheet = null;
    HSSFRow row = null;
    HSSFCell cell = null;               
    HSSFRow myRow = null;
    HSSFCell myCell = null;
    int sheets = workbook.getNumberOfSheets();          
    int fRow = 3;
    int lRow = 0;
    int count_row=0;

    //traversing through sheets in the 'file'
    for (int iSheet = 0; iSheet < sheets; iSheet++) {                   
        sheet = workbook.getSheetAt(iSheet);                
        if (sheet != null) {                                      
            lRow = sheet.getLastRowNum();
            for (int iRow = fRow; iRow <= lRow; iRow++) {
                row = sheet.getRow(iRow);
                //creating row in the new sheet
                myRow = mySheet.createRow(count_row++);
                if (row != null) {                           
                    for (int iCell = 0; iCell < 4; iCell++) {  
                        //creating a column in the new sheet
                        cell = row.getCell(iCell);
                        myCell = myRow.createCell(iCell);                                
                        myCell.setCellStyle(cs);
                        //setting cell type and adding data in each cell
                        if (cell != null ) {                                
                            myCell.setCellType(cell.getCellType());
                            switch (cell.getCellType()) {
                            case HSSFCell.CELL_TYPE_BLANK:                                      
                               myCell.setCellValue("");
                                break;

                            case HSSFCell.CELL_TYPE_BOOLEAN:
                                myCell.setCellValue(cell.getBooleanCellValue());
                                break;

                            case HSSFCell.CELL_TYPE_ERROR:
                                myCell.setCellErrorValue(cell.getErrorCellValue());
                                break;

                            case HSSFCell.CELL_TYPE_FORMULA:
                                myCell.setCellFormula(cell.getCellFormula());
                                break;

                            case HSSFCell.CELL_TYPE_NUMERIC:
                                if(HSSFDateUtil.isCellDateFormatted(cell))
                                    myCell.setCellValue(cell.getDateCellValue());
                                else
                                    myCell.setCellValue(cell.getNumericCellValue());
                                break;

                            case HSSFCell.CELL_TYPE_STRING:
                                myCell.setCellValue(cell.getStringCellValue());
                                break;
                            default:
                                myCell.setCellFormula(cell.getCellFormula());
                            }                                   
                        }
                    }
                }
            }
        }
    }
    bis.close();           
    copy_wb.write(bos);        
}

Answer:

I have reduced this to the main problem:

import org.apache.poi.hssf.usermodel.*;

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.BufferedOutputStream;

class CreateSingleExcelFile {

 public static void main(String[] args) throws IOException {
  CreateSingleExcelFile cef = new CreateSingleExcelFile();
  cef.fileIterator();
 }

//This is what you actual doing:
 public void fileIterator() throws IOException{
  HSSFWorkbook my_wb = new HSSFWorkbook();                        
  BufferedOutputStream bos= new BufferedOutputStream(new FileOutputStream("copiedWB.xls"));
  for(int i = 0; i < 3; i++){
   add_in_excel(my_wb, bos,"file" + i);
   System.out.println("In file :" + "file" + i);
  }
  bos.close(); //closing the BufferedOutputStream. The resulting file contains bytes for 3 complete XLS files. 
 }

 private void add_in_excel(HSSFWorkbook copy_wb, BufferedOutputStream bos, String file) throws IOException {
  HSSFSheet mySheet =  copy_wb.createSheet(file);
  copy_wb.write(bos); //write the copy_wb with one new added sheet into the BufferedOutputStream without closing it. But writing a XLS file is complex. So this will not work properly. It will append bytes for a complete XLS workbook onto the stream.
 }
}

You write the copy_wb with one new added sheet into the BufferedOutputStream without closing the stream. But writing a XLS file is complex. So this will not work properly. It will append bytes for a complete XLS workbook with at first 1, then 2 and at last 3 sheets onto the stream. But each time a complete XLS workbook file.

After adding all sheets, you close the BufferedOutputStream. The stream and also the resulting file contains bytes for 3 complete XLS files. The first with 1 sheet, the second with 2 sheets and the third with 3 sheets. If opened with Excel only the first will be read.

This will work, but is not recommend.

//This will work, but is not recommend
 public void fileIterator() throws IOException{
  HSSFWorkbook my_wb = new HSSFWorkbook();                        
  for(int i = 0; i < 3; i++){
   BufferedOutputStream bos= new BufferedOutputStream(new FileOutputStream("copiedWB.xls")); // creating a new BufferedOutputStream for each call of add_in_excel
   add_in_excel(my_wb, bos,"file" + i);
   System.out.println("In file :" + "file" + i);
  }
 }

 private void add_in_excel(HSSFWorkbook copy_wb, BufferedOutputStream bos, String file) throws IOException {
  HSSFSheet mySheet =  copy_wb.createSheet(file);
  copy_wb.write(bos);
  bos.close(); //write the copy_wb with one new added sheet into the BufferedOutputStream and close it.
 }

Creating a new BufferedOutputStream for each call of add_in_excel. Write the copy_wb with one new added sheet into the BufferedOutputStream and close it. So each write and close creates a new complete XLS file with one sheet more. Since it has the same name it will overwrite the existing file.

But why writing the complete workbook each time a new sheet is added?

So this is what I would do:

 public void fileIterator() throws IOException{
  HSSFWorkbook my_wb = new HSSFWorkbook();                        
  BufferedOutputStream bos= new BufferedOutputStream(new FileOutputStream("copiedWB.xls")); //create the BufferedOutputStream only for the fileIterator method
  for(int i = 0; i < 3; i++){
   add_in_excel(my_wb, "file" + i);
   System.out.println("In file :" + "file" + i);
  }
  my_wb.write(bos);
  bos.close();  //write into and close the BufferedOutputStream only once after you have added all sheets.
 }

 private void add_in_excel(HSSFWorkbook copy_wb, String file) throws IOException {
  HSSFSheet mySheet =  copy_wb.createSheet(file);
 }

Create the BufferedOutputStream only for the fileIterator method. Don't pass it to the add_in_excel. Write into and close the BufferedOutputStream only once after you have added all sheets.


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