How to create excel file from data table using NPOI in c# asp.net or MVC

Step 1 : Download or Install "NPOI" Nuget from package manager & "Newtonsoft" Nuget

Step 2 : Get Data in your datatable like

        DataTable dt1 = new DataTable();

            dt1.Columns.Add("ID");
            dt1.Columns.Add("Name");

            DataRow dr = dt.NewRow();
            dr["ID"] = "1";
            dr["Name"] = "Test";

            dt.Rows.Add(dr);

Step 3 : Create class

public class SummaryClass
{
   public string ID { get; set; }
   public string Name { get; set; }
}

Step 3 :

using NPOI.HSSF.UserModel;
using Newtonsoft.Json;

// Create Work Book
var workbook = new HSSFWorkbook();

// Add name of sheet
var sheet = workbook.CreateSheet("Daily Summary");

// convert your datatable to list

string JSON = JsonConvert.SerializeObject(dt);
var items = JsonConvert.DeserializeObject<List<SummaryClass>>(JSON);

// Create column & header string array
var columns = new[] { "ID", "Name" }; // Your DataTable Fields Name
var headers = new[] { "Sr. No.", "Client Name" }; // Header display name in excel

// Create row in excel sheet
var headerRow = sheet.CreateRow(0);

//create header
for (int i = 0; i < columns.Length; i++)
{
    var cell = headerRow.CreateCell(i);
    cell.SetCellValue(headers[i]);
}

//fill content
for (int i = 0; i < items.Count; i++)
{
    var rowIndex = i + 1;
    var row = sheet.CreateRow(rowIndex);

    for (int j = 0; j < columns.Length; j++)
    {
        var cell = row.CreateCell(j);
        var o = items[i];
        cell.SetCellValue(o.GetType().GetProperty(columns[j]).GetValue(o, null).ToString());
    }
}

// Store data in memory strem
var stream = new MemoryStream();
workbook.Write(stream);

//write to file
FileStream file = new FileStream("Your File Save Path", FileMode.CreateNew, FileAccess.Write);
stream.WriteTo(file);
file.Close();
stream.Close();