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Journey with Marvin: Path to Clean Architecture

Journey with Marvin: Path to Clean Architecture

A research on Java Spring validations led to an unexpected journey towards refactoring an application to adhere (somewhat) to Uncle Bob's Clean Architecture (https://blog.8thlight.com/uncle-bob/2012/08/13/the-clean-architecture.html)

Alan Yeo

May 27, 2016

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  1. What is Marvin? Chat bot interface that enables different chat

    clients to interact with the same backend application
  2. public class CustomerValidator implements Validator {
 private final Validator

 public CustomerValidator(Validator addressValidator) {
 if (addressValidator == null) {
 throw new IllegalArgumentException("The supplied [Validator] is " +
 "required and must not be null.");
 if (!addressValidator.supports(Address.class)) {
 throw new IllegalArgumentException("The supplied [Validator] must " +
 "support the validation of [Address] instances.");
 this.addressValidator = addressValidator;
 public boolean supports(Class clazz) {
 return Customer.class.isAssignableFrom(clazz);
 public void validate(Object target, Errors errors) {
 ValidationUtils.rejectIfEmptyOrWhitespace(errors, "firstName", "field.required");
 ValidationUtils.rejectIfEmptyOrWhitespace(errors, "surname", "field.required");
 Customer customer = (Customer) target;
 try {
 ValidationUtils.invokeValidator(this.addressValidator, customer.getAddress(), errors);
 } finally {
 } http://docs.spring.io/spring/docs/current/spring-framework-reference/html/validation.html#validator
  3. Annotation-style validations • Gives a clear correlation between fields and

    validations • Forces a declarative style of performing validations • Eliminates possibility of typo when specifying field to validate
  4. Structural vs Domain validations Structural: "name" string is not blank,

    "date" string matches a regex pattern, etc Domain: presence of Command object with some "name", uniqueness, etc
  5. Let's do a simple exercise to identify these two types!

    SlackController in `master` branch
  6. Learnings #5: Use Builder pattern to construct DTOs, especially when

    you have many arguments in the constructor Inspired by Item 2 of Joshua Bloch's Effective Java Second Edition book
  7. Learnings #6: Avoid throwing exceptions if possible and use a

    result object to encapsulate information
  8. Learnings #7: Handle exceptions at the right level of abstraction

    Inspired by Item 61 of Joshua Bloch's Effective Java Second Edition book
  9. What lies ahead? • Integration with CQRS and Event Sourcing

    • Integration with other chat clients (e.g. Telegram)