application · May 21, 2019

Turn Your Excel File Into a Web Application

Hawk Chen
Developer, Keikai.

A Typical Workflow Run by Excel

The other day a young lady in the administration department looked busy so I asked her what she was up to. She said that she has to visit several websites to check the currency rate, put them down in Excel and send it to her boss. The boss will then tell her to buy a certain currency at a certain amount. Finally, she has to keep the record in another Excel file. And this is one of her daily routines.

It is the year 2019. I was surprised that she still has to do lots of copy-paste routines and email Excel files around. My pride in being a developer wouldn't allow me, so I offered her that I will write a little program for her. Fortunately, with Keikai, I was able to do it in just 2 hours.

First, I asked her to lay out what she wishes to see in Excel. Then, I grabbed currency data from internet and populated it to the desired cells. Next, I implemented page navigation to smoothen the workflow and finally I generated a report. That’s it!

Let me describe in detail about how each step was done.

Build UI with Excel

The best thing about using Keikai is that it takes your Excel file and renders exactly the same in your browser. This means your Excel file is immediately turned into a web application UI.

This enables your business team, like the administrative lady, being able to join the system development easily by creating an Excel file as the UI.

So the admin lady sent me her Buy-Currency Excel file: on the first screen, she expects to see a selected list of countries and their currency, and the currency data should be populated automatically. On the second screen, she expects to input the buying amount and the exchanged amount, and lastly, she expects to see a report generated automatically containing Dates, Currency, and Amounts.

One-line importing

All I need to do here is to import the Excel file, and now the Excel template renders in my browser just like what she designed.

public static final String INTERNAL_BOOK_FOLDER = "/WEB-INF/book/";
public static final String BOOK_NAME = "currencyExchange.xlsx";
spreadsheet.importAndReplace(BOOK_NAME, new File(Configuration.DEFAULT_BOOK_FOLDER, BOOK_NAME));

Show Data in a Table

Next, I filled in currency exchange rates retrieved from European Central Bank by setValues() to the desired cells.

for (String currency :CURRENCY_LIST){
    spreadsheet.getRange(startingRow, 6, 1, 2).setValues(currency, rates.get(currency));

Now the admin lady can see the latest exchange rates being updated without visiting various websites.

Formula Supported

The Excel file she gave me contained formulas for calculating total exchanged amount according to the buying amount and exchange rate. But nothing to worry, I got formula supported on each cell out-of-the-box. Don't even need to enable it.

The lady can enter a formula according to her conditions without calculating numbers in her head, e.g. she can calculate how many notes she has in a cell and buys the same amount of USD.

When I call Range::getValue(), I can get the calculated result of that formula. No need to parse the formula by myself. Isn't great?

Page Navigation

Next, I will take care of page navigation – once she is done with the current page, take her to the next page. This can be done with activate(). The code below listens to the button clicking event and switches to another sheet.

private void addEventListener() {

    //listen to buy button
    exchangeSheet.getButton("Buy").addAction(buttonShapeMouseEvent -> {

    //listen to "buy another" button
    listSheet.getButton("BuyAnother").addAction(buttonShapeMouseEvent -> {

Control Accessibility

Now that the application workflow has been implemented, but we need to implement some “safety” to make sure that she follows the desired path. By default, a user can edit any cell in a typical Excel file or spreadsheet. But when making a Web application, usually we wish users to follow the flow we defined. The following APIs are handy for controlling accessibility.

Customize UI

I customize UI by hiding the toolbar, context menu and sheet tabs:

private void setupAccessibility() {

I prevent our administration lady from making undesired changes with these APIs, like deleting a sheet (page) by accident. There is another easier way through data attributes.

Limit Visible Area

Also, to let her concentrate on the application, I decided to show a proper area instead of showing her the whole sheet (16,384 columns and 1,048,576 rows) so the lady won't scroll to the end of the world (sheet):

private void setupVisibleArea() {

Protect a Sheet to be Read-only

But hiding toolbar and the context menu is not enough because users can still edit cells arbitrarily. Therefore, I enabled sheet protection to make the whole sheet read-only so that she won’t accidentally delete a currency row or change a currency rate.

public static final SheetProtection PROTECTION = new SheetProtection.Builder().setPassword("").setAllowSelectLockedCells(true).setAllowFiltering(true).build();
listSheet = spreadsheet.getWorksheet("list");

Since there are 17 different permissions of a SheetProtection, I create a SheetProtection object with a Builder pattern API, SheetProtection.Builder which is a more readable code style.

Limit Editable Area

Now that I’ve made the whole sheet read-only, she can’t edit anywhere. I need to unlock the cell where she needs to input the buying cost.

Unlock a cell

private void unlockCostInput() {
    Range costCell = spreadsheet.getRangeByName(exchangeSheet.getSheetId(), "cost");
    CellStyle unlockedStyle = costCell.createCellStyle();
    Protection protection = unlockedStyle.createProtection();
  • Line 2: I get a range by a defined name, and it can avoid code change even I move the input cell address. This approach has better code change resistance than getting by a cell address like C5.

So that cell (D7) becomes the only one editable cell in the read-only sheet:

Transaction Report

In the last page, I will show a list of currency transaction in a table.

private void placeAnOrder() {
    Range costCell = spreadsheet.getRangeByName(exchangeSheet.getSheetId(), COST_CELL);
    if (!costCell.toString().isEmpty()) {
        Double cost = costCell.getRangeValue().getCellValue().getDoubleValue();
        if (cost > 0) {
            Double amount = spreadsheet.getRangeByName(exchangeSheet.getSheetId(), "amount").getRangeValue().getCellValue().getDoubleValue();
            Range orderTable1stRow = spreadsheet.getRange(BOOK_NAME, listSheet.getSheetId(), "C6:G6");
            orderTable1stRow.getEntireRow().insert(Range.InsertShiftDirection.ShiftDown, Range.InsertFormatOrigin.RightOrBelow);
            orderTable1stRow.setValues(DateUtil.getExcelDate(new Date()), cost, destinationCurrency, destinationRate, amount);
  • Line 2: Since it's a protected sheet, I need to unprotect it before setting cell values.
  • Line 9-10: insert a new row and set values in a row at once.

Keikai also saves your efforts to maintain a table's style including background color, borders, font, and filters. When inserting and deleting rows. You just need to call insert(), and Keikai handles all changes on the related styles for you.

Filter Rows without Coding

Since I enable a filter in Excel, Keikai also enables it after importing. After the lady places an order for many times, she may wish to filter some rows according to the criteria, e.g. list only the EUR to USD transactions:

Filtered Result

Even if a filter was not enabled in the Excel file, I can enable the filter programmatically through Keikai API: setAutoFilter()

The whole usage is like:

I hope she will appreciate this little arrangement I made.

Through these steps, I can turn a traditional workflow of sending Excel forms into a web application. Then, those forms immediately become your system UI, and all my colleagues can effortlessly migrate to Keikai-based web system because they can execute workflows with a familiar UI without extra learning.

Source Code

I hope you enjoyed reading my article. The complete source code of "buy currency" application mentioned in this article is available at Github.

Just run the project and visit http://localhost:8080/dev-ref/case/exchange