How to read the data from .xlsx and convert the data into map

Question

I need to read the data from Excel sheet and need to convert the data in to key value pair.

I have written the below code.

Here is my code:

import java.io.File;  
import java.io.FileInputStream;  
import java.util.Iterator;  
import org.apache.poi.ss.usermodel.Cell;  
import org.apache.poi.ss.usermodel.Row;  
import org.apache.poi.xssf.usermodel.XSSFSheet;  
import org.apache.poi.xssf.usermodel.XSSFWorkbook;  

public class XLSXReaderExample  {  
    public static void main(String[] args) {  
       try {  
          File file = new File("C:\\demo\\employee.xlsx");   //creating a new file instance  
          FileInputStream fis = new FileInputStream(file);   //obtaining bytes from the file  
          //creating Workbook instance that refers to .xlsx file  
          XSSFWorkbook wb = new XSSFWorkbook(fis);   
          XSSFSheet sheet = wb.getSheetAt(0);     //creating a Sheet object to retrieve object  
          Iterator<Row> itr = sheet.iterator();    //iterating over excel file  
          while (itr.hasNext()){  
             Row row = itr.next();  
             Iterator<Cell> cellIterator = row.cellIterator();   //iterating over each column  
             while (cellIterator.hasNext()){  
                Cell cell = cellIterator.next();  
                switch (cell.getCellType()){  
                   case Cell.CELL_TYPE_STRING:    //field that represents string cell type  
                      System.out.print(cell.getStringCellValue() + "\t\t\t");  
                      break;  
                   case Cell.CELL_TYPE_NUMERIC:    //field that represents number cell type  
                      System.out.print(cell.getNumericCellValue() + "\t\t\t");  
                      break;  
                   case Cell.CELL_TYPE_Date:    //field that represents Date cell type
                      System.out.print(cell.getDateCellValue() + "\t\t\t");  
                      break; 
                   default:  
                }  
             }  
             System.out.println("");  
          }  
       }catch(Exception e){  
          e.printStackTrace();  
       }  
    }  
 } 

I get output as below:

Employee ID   Employee Name    Salary     Designation          Department   
1223.0         Harsh                      Marketing Manager    Marketing
3213.0         Vivek           15000.0    Financial Advisor    Finance  

However, I need the output as, all the header columns should come in the map key and the corresponding data should come as value. and one more thing is I should not hardcode the column names, I need to read from Excel dynamically each time the column headers can be different.

I need to set my data something like below format kindly help. Map<String, List<String>> myMaps = new HashMap<String, List<String>>();

Answer 1

As wrote in comment, since you cannot know if a cell contains header value or a data value what you want to do is impossible.

At first sight you have 2 way to achieve what you want:

• Try to have files with only one table, and the header row HAS to be always at the same excel row (see here) .
• Add a custom tag to header content: like <H> </H> , but of course if the files are used in visualization mode, this solution is not the best

EDIT:

You added a comment where confirm that the header is always at first line, and in file there is only 1 table, so the next code should work.

public static void main(String[] args) {
    try {
        File file = new File("C:\\demo\\employee.xlsx");   //creating a new file instance
        FileInputStream fis = new FileInputStream(file);   //obtaining bytes from the file
        //creating Workbook instance that refers to .xlsx file
        XSSFWorkbook wb = new XSSFWorkbook(fis);
        XSSFSheet sheet = wb.getSheetAt(0);     //creating a Sheet object to retrieve object
        Iterator<Row> itr = sheet.iterator();    //iterating over excel file

        // CAREFUL HERE! use LinkedHashMap to guarantee the insertion order!
        Map<String, List<String>> myMap = new LinkedHashMap<>();

        // populate map with headers and empty list
        if (itr.hasNext()) {
            Row row = itr.next();
            Iterator<Cell> headerIterator = row.cellIterator();
            while (cellIterator.hasNext()) {
                Cell cell = cellIterator.next();
                myMap.put(getCellValue(cell), new ArrayList<>());
            }
        }

        Iterator<List<String>> columnsIterator;
        // populate lists
        while (itr.hasNext()) {

            // get the list iterator every row to start from first list
            columnsIterator = myMap.values().iterator();
            Row row = itr.next();
            Iterator<Cell> cellIterator = row.cellIterator();   //iterating over each column
            while (cellIterator.hasNext()) {
                Cell cell = cellIterator.next();

                // here don't check hasNext() because if the file not contains problems
                // the # of columns is same as # of headers
                columnsIterator.next().add(getCellValue(cell));
            }
        }

        // here your map should be filled with data as expected

    } catch (Exception e) {
        e.printStackTrace();
    }
}

public static String getCellValue(Cell cell) {
    switch (cell.getCellType()) {
        case Cell.CELL_TYPE_STRING:    //field that represents string cell type
            return cell.getStringCellValue() + "\t\t\t";
        case Cell.CELL_TYPE_NUMERIC:    //field that represents number cell type
            return cell.getNumericCellValue() + "\t\t\t";
        case Cell.CELL_TYPE_Date:    //field that represents Date cell type
            return cell.getDateCellValue() + "\t\t\t";
        default:
            return "";
    }
}