step-1-hexagon.md

Hexagonal architecture

Kata goal

Implement the hexagonal architecture.

Business

Booking pallets have been sent to the application. We now want to compute the sum of all the exchanged pallets.

The two boundaries that we can already detect are the following:

• Provided use case: sum the bookings
• Needed to fulfill the request: have all the bookings

Steps

Implement the hexagon

Prepare

• Create booking package (new package for booking management)
• Create PalletBooking class with two fields
  • String partner
  • Long quantity

Application and port preparation

Present the feature to perform (Driver side)

• Create the booking.port.in package
• Create the ForCalculatingBookingSum interface
• Add the method Long computeSum()

Prepare the feature to code

• Create the BookingManager class in the booking package
• Add the implements ForCalculatingBookingSum to BookingManager
• Implement the method with a fake body

Test the method

• Create the BookingManagerTest
• Create a first test named sums
• Test that the method computeSum of the BookingManager returns a specific value

Example:

BookingManager bookingManager = new BookingManager();

Long sum = bookingManager.computeSum();

Assertions.assertThat(sum).isEqualTo(8L);

Present the needed system (Driven side)

• Create the booking.port.out package
• Create the ForGettingBookings interface
• Add the method Collection<PalletBooking> getBookings();

Use this needed system in the Manager

• Go in the BookingManager
• Create the field private final ForGettingBookings bookingsRepository;
• Create the constructor with the parameter
• Adapt the test to make it compile

Make the test green

• Create a ForGettingBookings manual mock without Mockito (new Class in the test for instance)
• Make the mock return the values needed to make the test green
• Code the rule in the BookingManager

Adapters part: Communication with external systems

Create the Driven adapter

• Create the booking.adapter.out package
• Create the FileBookingRepository that implements ForGettingBookings
• Implement the method that reads the file
• Create the csv file (here it will be located in C:\data\bookings.csv)

CSV content

FIRST PARTNER,5
SECOND PARTNER,8
THIRD PARTNER,10

Code Example

    @Override
    public Collection<PalletBooking> getBookings() {
        return loadPalletBookings();
    }
  
    private Collection<PalletBooking> loadPalletBookings() throws RuntimeException {
        try {
            List<String> fileContent = Files.readAllLines(Path.of("c:\\data\\bookings.csv"));
            return fileContent.stream()
                    .map(line -> new PalletBooking(line.split(",")[0], Long.parseLong(line.split(",")[1])))
                    .collect(Collectors.toList());
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

Create the Driver adapter

• Create the booking.adapter.in package
• Create the BookingRestController
  • Add @RestController and @RequestMapping("booking") at the top of the file
  • Create a method that do the bookingSum

Example:

    @GetMapping
    public ResponseEntity<Long> sumBookings() {
        return ResponseEntity.ok(forCalculatingBookingSum.computeSum());
    }

• Create the constructor without parameter
• Instanciate manually the BookingManager

Delegate the instanciation to spring

• Add the @Service on the top of the BookingManager
• Add the @Repository on the top of the FileBookingRepository
• Add the BookingManager parameter to the BookingRestController