Declarative_Clients_in_Spring - JNation

What is a declarative HTTP client vs an imperative one? Why are they useful and why should I care? We’ll talk about options that are available in the Spring Portfolio and what is coming on the horizon.

In this session, we will look at the history of declarative clients in Spring via Spring Cloud OpenFeign. We will also dive into upcoming options that are coming to Spring and the advantages that these new technologies bring to the developer experience.

Transcript

1. Olga Maciaszek-Sharma Declarative Clients in Spring Copyright © 2020 VMware, Inc. or its affiliates.
2. About Olga Software Engineer in Spring Cloud team Spring Cloud LoadBalancer, Spring Cloud OpenFeign, Spring Cloud Netflix, Spring Cloud Contract, Spring Cloud Square, RSocket HTTP Bridge
3. What is a declarative client?
4. Sample applications Customer Service Verification Service HTTP POST /verify Customer Verification Result
5. Direct use of HTTP client
6. Client interface
7. Implementation
8. Implementation with helper methods
9. Client interface usage
10. What if we could just create an annotated interface and have a library/ framework translate it into actual HTTP client requests?
11. Declarative/ interface client Client interface method calls HTTP calls Proxy
12. Feign
13. OpenFeign/Feign
14. Feign Java to HTTP client binder • Core part of a former Spring Cloud Netflix module, passed over to the community • Supports various HTTP clients, including Apache HTTP, Apache HC5, Ok HTTP • Contracts - support for custom annotations and argument resolution • Support for a broad range of encoders/ decoders, including Jackson and GSON • Metrics, including Micrometer support
15. Spring Cloud OpenFeign
16. Spring Cloud OpenFeign Spring MVC and Spring Cloud support for OpenFeign • Spring MVC annotations support • Auto-configurations for Feign-specific beans • Spring Cloud LoadBalancer support • Spring Cloud CircuitBreaker support • Tracing support
17. A declarative/ interface client
18. A declarative/ interface client use
19. Spring Cloud OpenFeign Demo Applications communicating over HTTP Customer Service SC OpenFeign Client SC LoadBalancer SC Sleuth Verification Service POST /verify Customer Verification Result Eureka Service Registry
20. Spring Cloud OpenFeign - popularity Highly-readable interface clients with robust integrations • 797 GitHub stars • 8670549 Maven downloads in 2021 • Nearly flat learning curve for Spring MVC users
21. Spring Cloud OpenFeign - issues • Issues with reusing client interfaces as controllers ◦ @RequestMapping at class level user issues (GH-547, GH-678) ◦ CVE-2021-22044 • Maintenance issues caused by dependence on third party upstream project • Lack of non-blocking support
22. Spring Cloud Square Spring Boot and Spring Cloud support for Retrofit and OkHttp • WebClient support for Retrofit interface clients • Auto-configurations • Load-balancing • Tracing • Only Retrofit annotations • Incubator project
23. RetroSocket Interface client for RSocket • Incubator project
24. Considerations More third-party integrations or an in-house solution? • HTTP/reactive, RSocket/RetroSocket - converging solutions • Opportunity to create a first-class solution in the Spring Framework ◦ No maintenance dependence on third party projects • Previous Spring Cloud support built around external projects ◦ Possibility of providing integration on top of the Spring Framework interface clients
25. HTTP & RSocket Interface Clients in Spring Framework 6.0
26. Interface clients are not new in the Spring Framework Same mechanism, different protocols
27. Why HTTP and RSocket now? Discussions with Spring Cloud around OpenFeign, Retrofit, and RSocket integrations
28. Spring Framework 6.0 already had plans for RSocket interface client
29. Old request for HTTP, deferred to… Spring Cloud OpenFeign
30. Old request for HTTP, deferred to… Spring Cloud OpenFeign
31. Opportunity to revisit Underlying mechanism is not specific to Spring Cloud Cloud features are extensions on top
32. Some issues can only be addressed in Spring Framework programming model vs reusing @RequestMapping
33. Decided to explore for Spring Framework 6.0
34. HTTP interface client programming model Relationship to server @RequestMapping?
35. Two goals Define a single request (no wildcards of any kind!) Avoid outright server-specific
36. @RequestMapping attributes For mapping of 1..N requests Any HTTP method Any URL path
37. @RequestMapping method parameters ServletRequest HttpMethod @RequestHeader @RequestParam @RequestBody @RequestAttribute @ModelAttribute …
38. @RequestMapping return values ResponseEntity HttpHeaders Body void Model View SseEmitter …
39. New method annotation to declare rather than map requests @RequestMapping @HttpExchange
40. @HttpExchange attributes url method contentType accept
41. @HttpExchange method parameters Subset of those for @RequestMapping i.e. reusing method parameter annotations
42. @HttpExchange method parameters URI HttpMethod @RequestHeader @PathVariable @RequestBody @RequestParam @CookieValue
43. @HttpExchange return values Subset of those for @RequestMapping i.e. also using return value types
45. Blocking
46. Reactive
47. status, headers, body
48. headers
49. execute only
51. Spring Boot can declare this as a bean
52. RSocket interface client planned for Spring Framework 6.0 M5
53. Resources • Demo code • Spring Cloud OpenFeign • Spring Framework documentation for HTTP interface client • Spring Cloud Square • RetroSocket
54. Thank you Twitter: @olga_maciaszek © 2020 Spring. A VMware-backed project.