Reading and Writing data to excel file using Apache POI

Earlier in this post, we introduced Apache POI- a Java API useful for interacting with Microsoft office documents.
Now we’ll see how can we read and write to an excel file using the API.

Writing an excel file

Writing a file using POI is very simple and involve following steps:

Create a workbook
Create a sheet in workbook
Create a row in sheet
Add cells in sheet
Repeat step 3 and 4 to write more data

// import statements 
public class POIforgfgWrite { 
public static void main(String[] args) 
    { 
        // Blank workbook 
        XSSFWorkbook workbook = new XSSFWorkbook(); 
  
        // Create a blank sheet 
        XSSFSheet sheet = workbook.createSheet("student Details"); 
  
        // This data needs to be written (Object[]) 
        Map<String, Object[]> data = new TreeMap<String, Object[]>(); 
        data.put("1", new Object[]{ "ID", "NAME", "LASTNAME" }); 
        data.put("2", new Object[]{ 1, "Pankaj", "Kumar" }); 
        data.put("3", new Object[]{ 2, "Prakashni", "Yadav" }); 
        data.put("4", new Object[]{ 3, "Ayan", "Mondal" }); 
        data.put("5", new Object[]{ 4, "Virat", "kohli" }); 
  
        // Iterate over data and write to sheet 
        Set<String> keyset = data.keySet(); 
        int rownum = 0; 
        for (String key : keyset) { 
            // this creates a new row in the sheet 
            Row row = sheet.createRow(rownum++); 
            Object[] objArr = data.get(key); 
            int cellnum = 0; 
            for (Object obj : objArr) { 
                // this line creates a cell in the next column of that row 
                Cell cell = row.createCell(cellnum++); 
                if (obj instanceof String) 
                    cell.setCellValue((String)obj); 
                else if (obj instanceof Integer) 
                    cell.setCellValue((Integer)obj); 
            } 
        } 
        try { 
            // this Writes the workbook gfgcontribute 
            FileOutputStream out = new FileOutputStream(new File("gfgcontribute.xlsx")); 
            workbook.write(out); 
            out.close(); 
            System.out.println("gfgcontribute.xlsx written successfully on disk."); 
        } 
        catch (Exception e) { 
            e.printStackTrace(); 
        } 
    } 
} 

Reading an excel file

Reading an excel file is also very simple if we divide this in steps.

br>

Create workbook instance from excel sheet
Get to the desired sheet
Increment row number
iterate over all cells in a row
repeat step 3 and 4 until all data is read

// import statements 
public class POIforgfgRead { 
public static void main(String[] args) 
    { 
        try { 
            FileInputStream file = new FileInputStream(new File("gfgcontribute.xlsx")); 
  
            // Create Workbook instance holding reference to .xlsx file 
            XSSFWorkbook workbook = new XSSFWorkbook(file); 
  
            // Get first/desired sheet from the workbook 
            XSSFSheet sheet = workbook.getSheetAt(0); 
  
            // Iterate through each rows one by one 
            Iterator<Row> rowIterator = sheet.iterator(); 
            while (rowIterator.hasNext()) { 
                Row row = rowIterator.next(); 
                // For each row, iterate through all the columns 
                Iterator<Cell> cellIterator = row.cellIterator(); 
  
                while (cellIterator.hasNext()) { 
                    Cell cell = cellIterator.next(); 
                    // Check the cell type and format accordingly 
                    switch (cell.getCellType()) { 
                    case Cell.CELL_TYPE_NUMERIC: 
                        System.out.print(cell.getNumericCellValue() + "t"); 
                        break; 
                    case Cell.CELL_TYPE_STRING: 
                        System.out.print(cell.getStringCellValue() + "t"); 
                        break; 
                    } 
                } 
                System.out.println(""); 
            } 
            file.close(); 
        } 
        catch (Exception e) { 
            e.printStackTrace(); 
        } 
    } 
} 

Output:
Output

Sometimes you need to read a file at different location: Here’s how you can do it:

private static final String FILE_NAME 
    = "C:\Users\pankaj\Desktop\projectOutput\mobilitymodel.xlsx"; 
public static void write() throws IOException, InvalidFormatException 
{ 
    InputStream inp = new FileInputStream(FILE_NAME); 
    Workbook wb = WorkbookFactory.create(inp); 
    Sheet sheet = wb.getSheetAt(0); 
    ........ 
} 

You can append to the existing file using following code:

private static final String FILE_NAME 
    = "C:\Users\pankaj\Desktop\projectOutput\blo.xlsx"; 
public static void write() throws IOException, InvalidFormatException 
{ 
    InputStream inp = new FileInputStream(FILE_NAME); 
    Workbook wb = WorkbookFactory.create(inp); 
    Sheet sheet = wb.getSheetAt(0); 
    int num = sheet.getLastRowNum(); 
    Row row = sheet.createRow(++num); 
    row.createCell(0).setCellValue("xyz"); 
    ..... 
        .. 
        // Now this Write the output to a file 
        FileOutputStream fileOut = new FileOutputStream(FILE_NAME); 
    wb.write(fileOut); 
    fileOut.close(); 
} 

References :
https://poi.apache.org/
https://poi.apache.org/spreadsheet/examples.html
https://poi.apache.org/apidocs/

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.

Reading and Writing data to excel file using Apache POI

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