Simple Web Development in Java

Vincent Tencé@testinfected

http://vtence.comhttp://github.com/testinfected

Déjà vu?

You start a new project by assembling multiple libraries and frameworks

It’s a lot of initial complexity

One of the frameworks keeps getting in the way

The framework feels like a prison

It keeps surprising you with unintended behaviour

The Original Version

• Spring with Spring MVC

• Velocity and SiteMesh, UrlRewriteFilter

• Hibernate, JPA, MySQL

• Hibernate Validator

• Maven

• ... 53 jars!

http://thepresentationdesigner.co.uk/blog/portfolio-item/bruce-lee-slide-2/

The Challenge

• Use simple tools and libraries

• Framework (Web, ORM, DI)

• DIYS (Do It Yourself Simply)

• Ease of assembly, configuration and deployment

• Minimum startup and shutdown costs

• XML

• Annotations

The Simple Version

• Simple

• Mustache

• JDBC and MySQL

• CLI

• Buildr

• 4 jars

Build File

define 'petstore', [..] do define 'domain' do compile.with test.with HAMCREST package :jar end

define 'persistence' do compile.with project(:domain) test.with HAMCREST, :flyway, :mysql, NO_LOG, [...] package :jar end

define 'webapp' domain compile.with :simpleframework, :jmustache, [...] test.with HAMCREST, :antlr_runtime, :cssselectors, :hamcrest_dom, [...] test.with transitive(artifacts(:nekohtml, :htmlunit, :jmock_legacy))

package :jar end[...]end

Dependency Injection

AttachmentStorage attachments = new FileSystemPhotoStore("/photos");Connection connection = new ConnectionReference(request).get();Transactor transactor = new JDBCTransactor(connection);ProductCatalog products = new ProductsDatabase(connection);ItemInventory items = new ItemsDatabase(connection);OrderBook orders = new OrdersDatabase(connection);ProcurementRequestHandler procurement =

new PurchasingAgent(products, items, transactor)OrderNumberSequence orderNumbers = new OrderNumberDatabaseSequence(connection);Cashier cashier = new Cashier(orderNumbers, orders, transactor);Messages messages =

new BundledMessages(ResourceBundle.getBundle("ValidationMessages"))

Router router = Router.draw(new DynamicRoutes() {{[...]

}});

Routing

[...]

Router router = Router.draw(new DynamicRoutes() {{ get("/products").to(new ListProducts(products, attachments, pages.products())); post("/products").to(new CreateProduct(procurement)); get("/products/:product/items").to(new ListItems(items, pages.items())); post("/products/:product/items").to(new CreateItem(procurement)); get("/cart").to(new ShowCart(cashier, pages.cart())); post("/cart").to(new CreateCartItem(cashier)); get("/orders/new").to(new Checkout(cashier, pages.checkout())); get("/orders/:number").to(new ShowOrder(orders, pages.order())); post("/orders").to(new PlaceOrder(cashier)); delete("/logout").to(new Logout()); map("/").to(new StaticPage(pages.home()));}});

MVC

public class ShowOrder implements Application { private final OrderBook orderBook; private final Page orderPage;

public ShowOrder(OrderBook orderBook, Page orderPage) { this.orderBook = orderBook; this.orderPage = orderPage; }

public void handle(Request request, Response response) throws Exception { String number = request.parameter("number"); Order order = orderBook.find(new OrderNumber(number)); orderPage.render(response, context().with("order", order)); }}

Data Access

public class OrdersDatabase implements OrderBook { [...] public OrdersDatabase(Connection connection) { this.connection = connection; }

private List<LineItem> findLineItemsOf(Order order) { return Select.from(lineItems). where("order_id = ?", idOf(order).get()). orderBy("order_line"). list(connection); }

private Order findOrder(OrderNumber orderNumber) { return Select.from(orders, "_order"). leftJoin(payments, "payment", "_order.payment_id = payment.id"). where("_order.number = ?", orderNumber). first(connection); } [...]}

Transactions

public class Cashier implements SalesAssistant { [...] public OrderNumber placeOrder(PaymentMethod paymentMethod) throws Exception {

[...] QueryUnitOfWork<OrderNumber> order = new QueryUnitOfWork<OrderNumber>() { public OrderNumber query() throws Exception { OrderNumber nextNumber = orderNumberSequence.nextOrderNumber(); final Order order = new Order(nextNumber); order.addItemsFrom(cart); order.pay(paymentMethod); orderBook.record(order); cart.clear(); return nextNumber; } }; return transactor.performQuery(order); } [...]}

Validation Constraints

public class CreditCardDetails extends PaymentMethod implements Serializable { private final CreditCardType cardType; private final Constraint<String> cardNumber; private final NotNull<String> cardExpiryDate; private final Valid<Address> billingAddress;

public CreditCardDetails(CreditCardType type, String number, String expiryDate, Address billingAddress) {

this.cardType = type; this.cardNumber = Validates.both(notEmpty(number),

correctnessOf(type, number)); this.cardExpiryDate = Validates.notNull(expiryDate); this.billingAddress = Validates.validityOf(billingAddress); }

public String getCardNumber() { return cardNumber.get(); } [...]}

Validation

public class Validator {

public <T> Set<ConstraintViolation<?>> validate(T target) { Valid<T> valid = Validates.validityOf(target); valid.disableRootViolation(); ViolationsReport report = new ViolationsReport(); valid.check(Path.root(target), report); return report.violations(); }

[...]}

Forms

public class PaymentForm extends Form {

public static PaymentForm parse(Request request) { return new PaymentForm(new CreditCardDetails( valueOf(request.parameter("card-type")), request.parameter("card-number"), request.parameter("expiry-date"), new Address(request.parameter("first-name"), request.parameter("last-name"), request.parameter("email")))); }

private final Valid<CreditCardDetails> paymentDetails;

public PaymentForm(CreditCardDetails paymentDetails) { this.paymentDetails = Validates.validityOf(paymentDetails); }

public CreditCardType cardType() { return paymentDetails().getCardType(); } public CreditCardDetails paymentDetails() { return paymentDetails.get(); }}

Thoughts

• Not very “enterprisy”

• What are we missing?

• Use a proven solution or develop our own?

• Not a silver bullet

Takeaways

• Avoid the temptation of frameworks

• Use simple tools that do one thing and do it well

• Build your own tools

• Copy the best ideas; write only the simple code you need

• Keep your tools simple and specialized

Thanks!

• Simple version :https://github.com/testinfected/simple-petstore

• Spring version :https://github.com/testinfected/petstore

•Web :https://github.com/testinfected/molecule

• Data Mapping :https://github.com/testinfected/tape