here I am trying to export JTable into excel file...I didn't get any error on console...but on excel sheet I got only column names...my aim is want to show database table in this JTable square, and below this there is Export button,so after clicking this button excel file should be created for above displaying JTable.

so cant recognized actual error

    JButton btnExport = new JButton("Export");
    btnExport.addActionListener(new ActionListener() 
    {
        public void actionPerformed(ActionEvent arg0)
        {
            try 
            {
                String query="Select * from client";
                PreparedStatement pst=conn.prepareStatement(query);
                ResultSet rs=pst.executeQuery();
                table.setModel(DbUtils.resultSetToTableModel(rs));

                HSSFWorkbook wb = new HSSFWorkbook();
                HSSFSheet sheet = wb.createSheet("Excel Sheet");
                HSSFRow rowhead = sheet.createRow(0);
                rowhead.createCell(0).setCellValue("Client_Vendor code");
                rowhead.createCell(1).setCellValue("Client_Name");
                rowhead.createCell(2).setCellValue("Purchaser_Name");
                rowhead.createCell(3).setCellValue("User_Name");
                rowhead.createCell(4).setCellValue("Sales_Engg");

                int index=1;
                while(rs.next())
                    {
                    HSSFRow row = sheet.createRow(index);
                    row.createCell(0).setCellValue(rs.getInt(1));
                    row.createCell(1).setCellValue(rs.getString(2));
                    row.createCell(2).setCellValue(rs.getString(3));
                    row.createCell(3).setCellValue(rs.getString(4));
                    row.createCell(4).setCellValue(rs.getString(5));
                    index++;

                    }  

                    FileOutputStream fileOut = new FileOutputStream("e:/CLIENTDATA/client.xlsx");
                    wb.write(fileOut);
                    fileOut.close();
                    System.out.println("Data is saved in excel file.");
                 }
                catch (Exception e) 
            {
                e.printStackTrace();
            }

So your problem is right here...

table.setModel(DbUtils.resultSetToTableModel(rs));

DBUtils is reading to the end of the ResultSet, meaning when you call rs.next(), it returns false, because there is no more data

You have two chocies...

You Could...

Call ResultSet#beforeFirst, but this is not supported by all database and there may be a performance hit

You Could...

Stop using DBUtils and build the TableModel manually. Start by having a look at How to Use Tables for more details

ResultSet rs = pst.executeQuery();
ResultSetMetaData rsmd = rs.getMetaData();
int columnCount = rsmd.getColumnCount();

HSSFWorkbook wb = new HSSFWorkbook();
HSSFSheet sheet = wb.createSheet("Excel Sheet");
HSSFRow rowhead = sheet.createRow(0);

DefaultTableModel model = new DefaultTableModel();
for (int col = 0; col < columnCount; col++) {
    String columnName = rsmd.getColumnName(col + 1);
    model.addColumn(columnName);
    rowhead.createCell(col).setCellValue(columnName);
}

int index = 1;
while (rs.next()) {
    Vector tableRow = new Vector(columnCount);
    HSSFRow row = sheet.createRow(index);
    for (int col = 0; col < columnCount; col++) {
        Object value = rs.getObject(col + 1);
        if (value instanceof Integer) {
            row.createCell(col).setCellValue((int) value);
            tableRow.add((int) value);
        } else {
            row.createCell(col).setCellValue(value.toString());
            tableRow.add(value.toString());
        }
    }
    model.addRow(tableRow);
}

try (FileOutputStream fileOut = new FileOutputStream("e:/CLIENTDATA/client.xlsx")) {
    wb.write(fileOut);
}

I'd also recommend having a look at JDBC Database Access and The try-with-resources Statement