Learn: how Finance Lab is built

Spring Boot 3.5 · Java 21 · Spring Data JPA + JdbcTemplate · Flyway · SQL Server · Thymeleaf

The one idea behind everything: double entry

Every feature ends in a journal entry whose debits equal its credits. Reports never read invoices or bills - they read the journal lines through the view v_ledger. That is why the trial balance always balances and why the balance sheet, P&L and cash flow agree with each other.

Account type	Grows with	Examples
Asset	Debit	Bank, receivables, input VAT, laptops
Expense	Debit	Salaries, rent, FX loss
Liability	Credit	Payables, output VAT, WHT payable, loan
Equity	Credit	Share capital, retained earnings
Revenue	Credit	Software sales, consulting, FX gain

Layers - where to look

`db/migration`	Flyway SQL: tables, CHECK / UNIQUE constraints, filtered index, computed columns, the view v_ledger, master data
`domain`	JPA entities (Lombok getters / setters), enums stored as text
`repo`	Spring Data repositories, derived queries, @EntityGraph
`service`	Posting rules (@Transactional), reports with NamedParameterJdbcTemplate, BigDecimal money rules
`web`	Controllers, form binding + Bean Validation, PRG pattern (redirect after POST), SVG charts
`config`	DemoDataSeeder - ten months of sample data posted through the real services

Feature map 411 - 430

Every page has a "How this works" panel at the bottom with the concepts, the classes to read and its SQL.

411 Record income

Money received straight away, without an invoice.

412 Record expenses

Money paid straight away: salaries, supplies, travel, fees.

413 General ledger

Chart of accounts, trial balance, journals and account ledgers.

414 Balance sheet

Assets = Liabilities + Equity on any date.

415 Profit & loss

Revenue - cost of sales - expenses = net profit, with comparison.

416 Cash flow

Where the cash came from and where it went.

417 Accounts payable

Vendor bills, what we owe, and paying them.

418 Accounts receivable

Who owes us what, and for how long.

419 Invoices

Sales invoices with lines, VAT, due dates and status.

420 Receipts

Money received against an invoice, full or partial.

421 Credit notes

Reduce what a customer owes: discount, return or mistake.

422 Tax calculator

VAT in / out, withholding tax with gross-up, personal income tax.

423 VAT report

Output VAT - input VAT per month (PP 30) with the tax invoice lists.

424 Withholding tax

Tax we withheld (PND 3 / PND 53) and tax withheld from us.

425 Budgets

A 12-month budget per account and cost center.

426 Budget vs actual

How much of the budget is used, and where it is over.

427 Cost centers

Departments that own revenue, costs and budgets.

428 Multi-currency

Documents in USD, EUR, JPY ... and the FX gains and losses.

429 Exchange rates

Daily rates, history chart and 'rate on a date'.

430 Payment tracking

Everything still to be paid or received, by due date.

Exercises

Record an expense with VAT 7 % and a withholding tax type, then open its journal entry: which four lines were posted?
Create an invoice in USD, then receive it on a later date. Find the FX gain or loss line (428).
Issue a credit note and watch the VAT report (423) for that month change.
Post a manual journal that does not balance - read the error from JournalService.post.
Make one cost center's budget smaller and open Budget vs actual (426).
Run the SQL from a "How this works" panel in SQL Server Management Studio against FinanceLabDB.

Start again

Deletes every transaction (invoices, bills, journals, budgets, exchange rates) and creates the sample data again. Accounts, contacts and cost centers stay.