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)

Transcript

1. Journey with Marvin Path towards Clean Architecture
2. What is Marvin? Chat bot interface that enables different chat clients to interact with the same backend application
3. Marvin Your App Issues command Send request Sends response Returns result
4. How it started Researching on how validations are done in Spring
5. public class CustomerValidator implements Validator {
 
 private final Validator addressValidator;
 
 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 {
 errors.pushNestedPath("address");
 ValidationUtils.invokeValidator(this.addressValidator, customer.getAddress(), errors);
 } finally {
 errors.popNestedPath();
 }
 }
 } http://docs.spring.io/spring/docs/current/spring-framework-reference/html/validation.html#validator
6. How it started Can we do better than this?
7. Annotation-style vs Validator implementation
8. Let's see some code! IncomingSlackRequest in `alan/javax-validation` and `master` branches
9. 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
10. Annotation-style validations Can we do better than this?
11. Let's see some code! SlackController in `01-annotation-style-validations` tag
12. 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
13. Let's do a simple exercise to identify these two types! SlackController in `master` branch
14. Doesn't that sound familiar to what Uncle Bob shared?
15. https://blog.8thlight.com/uncle-bob/2012/08/13/the-clean-architecture.html
16. Perhaps, we can perform structural validations in the controllers and domain validations within our use cases?
17. And the journey begins...
18. Let's see some code! SlackController in `alan/javax-validation` branch
19. Learnings
20. Learnings #1: Use Data Transfer Objects (DTOs) when crossing boundaries between layers
21. Learnings #2: Perform structural validations on DTOs
22. Learnings #3: Use Adapter objects to pick necessary fields for next layer
23. Learnings #4: Enforce preconditions
24. 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
25. Learnings #6: Avoid throwing exceptions if possible and use a result object to encapsulate information
26. Learnings #7: Handle exceptions at the right level of abstraction Inspired by Item 61 of Joshua Bloch's Effective Java Second Edition book
27. Learnings #8: Inject dependencies via constructor and avoid reliance on framework
28. Learnings #9: Depend on abstractions (i.e. interfaces) rather than concretions (i.e. implementations)
29. Afterthoughts
30. Video: https://www.youtube.com/watch?v=WpkDN78P884 Slides: https://twitter.com/unclebobmartin/status/137887150883618818
31. Video: https://www.youtube.com/watch?v=WpkDN78P884 Slides: https://twitter.com/unclebobmartin/status/137887150883618818
32. Video: https://www.youtube.com/watch?v=WpkDN78P884 Slides: https://twitter.com/unclebobmartin/status/137887150883618818
33. Video: https://www.youtube.com/watch?v=WpkDN78P884 Slides: https://twitter.com/unclebobmartin/status/137887150883618818
34. Video: https://www.youtube.com/watch?v=WpkDN78P884 Slides: https://twitter.com/unclebobmartin/status/137887150883618818
35. Video: https://www.youtube.com/watch?v=WpkDN78P884 Slides: https://twitter.com/unclebobmartin/status/137887150883618818
36. Afterthoughts The architectural reasons behind it becomes obvious as you go through the refactoring process
37. What lies ahead? • Integration with CQRS and Event Sourcing • Integration with other chat clients (e.g. Telegram)
38. That's it! Thank you!
39. Alan Yeo a http://github.com/pivotal-sg/marvin-bot ayeo@pivotal.io