ARE YOU STRINGIFIED?

About me

Frederik Hahne

@atomfrede

@java_hipster board member

@jugpaderborn leader

developer @wescalehq

About         escale

• latest Javascript technologies (React, VueJS, Redux, Webpack & friends)
• latest Java technologies (Spring Boot, Vert.x, Gradle)
• Cloud Native (Kubernetes, Spring Cloud)
• Microservices, Microfrontends
• API 1st
• 3rd party integration
• Agile, diverse, open minded teams

ARE YOU STRINGIFIED?

Java
Go

Haskell
Kotlin

TYPED

statically

public class Customer {

    private Long id;
    private String firstname, lastname, email;
}

Typed

public class Customer {

    private Long id;
    private String firstname, lastname, email;
}

public class SomeService {

    Customer createCustomer(..., String email, ...) {

         // What is a valid email adress?
        // Which parameter is the email?
    }
}

Typed?

public class Customer {

    private Long id;
    private String firstname, lastname, email;
}

public class SomeService {

    Customer createCustomer(..., String email, ...) {

         // What is a valid email adress?
    }
}

Stringly Typed :(

public class Customer {

    private Long id;
    private Firstname firstname;
    private Lastname lastname;
    private Email email;
}

public class SomeService {

    public Customer createCustomer(..., Email email, ...) {
        
        return new Customer(..., email, ...);
    }
}

Make Concepts Explicit in Code

Patterns
Libraries
Languages

Builder Pattern

Customer person = new Builder()
               .firstname("John")
               .lastname("Doe")
               .email("john@doe.me")
               .build();

Libraries

public Customer(@Firstname String firstname, 
                @Lastname String lastname, 
                @Email String email) {
    // Use Bean Validation to externalize validation of string
}

// Using value objects to let the 
// apt compiler generate a lot of code
@Value.Immutable
public interface Customer {
    private Email email;
}

@Value.Immutable
public interface Email {
    private String email;
}
// Generate builders, validators at compile time

Languages

typealias Firstname = String
typealias Lastname = String
typealias Email = String

class Customer(val firstname: Firstname, 
               val lastname: Lastname,
               val email: Email)

val customer = Customer("John", 
                        "Doe", 
                        "john@doe.me")

Can we do better?

• Declaration: Typed
• Invocation: Not :(
• It's just an alias

Languages

class Customer(val firstname: String, 
                val lastname: String, 
                val email: String? = null)

val customer = Customer(firstname = "John", 
                        lastname = "Doe")

val another = Customer(lastname = "Mueller",
                        email = "hans@mueller.de",
                        firstname = "Hans")

One more thing...

Tooling

Remember:

Excplicit is better

More

• https://speakerdeck.com/olivergierke/ddd-and-rest-domain-driven-apis-for-the-web-5
• https://blog.frankel.ch/coping-stringly-typed/
• http://immutables.github.io/

Join our Meetup

29.06.17 um 18:30 Uhr

An der Talle 89

@wescalehq

Was ist Serverless Computing?

Vortrag mit Diskussion

Frank Pientka (JUG Dortmund)

https://jug-pb.gitlab.io/

Join our Meetup

Im August

@verlinked

Effiziente Datenpersistierung mit JPA und Hibernate

Vortrag mit Diskussion

Thorben Janssen (CDI 2.0 expert group member)

https://jug-pb.gitlab.io/

Eclipse Demo Camp

Tuesday, June 27th, 2017, 18:15

"Biohaus Bauwerker" - Driburger Straße 24 - 33100 Paderborn

https://wiki.eclipse.org/Eclipse_DemoCamps_Oxygen_2017/Paderborn

https://www.meetup.com/itemis/events/240477045/?eventId=240477045

Question?