1. GregLTurnquist.com/springone2020
Building Flexible APIs
with Spring HATEOAS
September 2–3, 2020
springone.io
1

2. GregLTurnquist.com/springone2020
Who am I?

3. GregLTurnquist.com/springone2020
Who am I?

4. GregLTurnquist.com/springone2020
Who am I?
bit.ly/hacking-with-spring-boot

5. GregLTurnquist.com/springone2020
Who am I?
bit.ly/hacking-with-spring-boot
● Principal developer on
the Spring team
● Nashville JUG co-founder
● Committer & Project
Lead for several Spring
projects
● YouTube/GregTurnquist

6. GregLTurnquist.com/springone2020
Let’s talk about…APIs!

7. GregLTurnquist.com/springone2020
What is an API?

8. GregLTurnquist.com/springone2020
What is an API?
● Place to get a little JSON/XML/whatever?

9. GregLTurnquist.com/springone2020
What is an API?
● Place to get a little JSON/XML/whatever?
● Way to interact with the app?

10. GregLTurnquist.com/springone2020
What is an API?
● Place to get a little JSON/XML/whatever?
● Way to interact with the app?
● Means to extract value from another app to help your own app?

11. GregLTurnquist.com/springone2020
What is an API?
● Place to get a little JSON/XML/whatever?
● Way to interact with the app?
● Means to extract value from another app to help your own app?
Let’s dig in and discover what it means to have a flexible API!

12. GregLTurnquist.com/springone2020
Simple API
6
● Spring MVC
● Simple
● Clear separation between layers

13. GregLTurnquist.com/springone2020
Simple API
6
● Spring MVC
● Simple
● Clear separation between layers

14. GregLTurnquist.com/springone2020
Simple API
6
● Spring MVC
● Simple
● Clear separation between layers

15. GregLTurnquist.com/springone2020
Simple API
6
● Spring MVC
● Simple
● Clear separation between layers

16. GregLTurnquist.com/springone2020
Simple API
6
● Spring MVC
● Simple
● Clear separation between layers

17. GregLTurnquist.com/springone2020
Simple API
{
"id": 0,
"name": "Frodo",
"role": "ring bearer"
}
6

18. GregLTurnquist.com/springone2020
Simple API
{
"id": 0,
"name": "Frodo",
"role": "ring bearer"
}
6
● Data and…

19. GregLTurnquist.com/springone2020
Simple API
{
"id": 0,
"name": "Frodo",
"role": "ring bearer"
}
6
● Data and…
● …nothing else!

20. GregLTurnquist.com/springone2020
Simple API
{
"id": 0,
"name": "Frodo",
"role": "ring bearer"
}
6
● Data and…
● …nothing else!
● Some value, but what about…

21. GregLTurnquist.com/springone2020
Simple API
{
"id": 0,
"name": "Frodo",
"role": "ring bearer"
}
6
● Data and…
● …nothing else!
● Some value, but what about…
● …updates?

22. GregLTurnquist.com/springone2020
Simple API
{
"id": 0,
"name": "Frodo",
"role": "ring bearer"
}
6
● Data and…
● …nothing else!
● Some value, but what about…
● …updates?
● …breaking changes?

23. GregLTurnquist.com/springone2020
Simple API
{
"id": 0,
"name": "Frodo",
"role": "ring bearer"
}
6
● Data and…
● …nothing else!
● Some value, but what about…
● …updates?
● …breaking changes?
● …backwards compatibility?

24. GregLTurnquist.com/springone2020
What happens when…
6

25. GregLTurnquist.com/springone2020
What happens when…
6

26. GregLTurnquist.com/springone2020
What happens when you serve this…
{
"id": 0,
"firstName": "Frodo",
"lastName": "Baggins",
"role": "ring bearer"
}
6

27. GregLTurnquist.com/springone2020
…but older clients try this?
6

28. GregLTurnquist.com/springone2020
…but older clients try this?
6
● What now?

29. GregLTurnquist.com/springone2020
…but older clients try this?
6
● What now?
● Tell users to just use your new API?

30. GregLTurnquist.com/springone2020
…but older clients try this?
6
● What now?
● Tell users to just use your new API?
● Roll out another version?

31. GregLTurnquist.com/springone2020
…but older clients try this?
6
● What now?
● Tell users to just use your new API?
● Roll out another version?
● Handle this AND the new format?

32. GregLTurnquist.com/springone2020
What about versioning?
6
https://www.infoq.com/news/2013/12/api-versioning/
● Knot = Single version of API
● P2P = Multiple versions
● Compatible = One API supports
multiple versions

33. GregLTurnquist.com/springone2020
What about versioning?
6
It is always possible for some unexpected reason to come along that requires a completely
different API, especially when the semantics of the interface change or security issues require the
abandonment of previously deployed software. My point was that there is no need to anticipate
such world-breaking changes with a version ID. We have the hostname for that. What you are
creating is not a new version of the API, but a new system with a new brand.
On the Web, we call that a new website. Websites don’t come with version numbers attached
because they never need to. Neither should a RESTful API. A RESTful API (done right) is just a
website for clients with a limited vocabulary.
—Dr. Roy Fielding
“

34. GregLTurnquist.com/springone2020
How rough can deprecating APIs be?
6
http://bit.ly/deprecating-apis

35. GregLTurnquist.com/springone2020
Just do this…
6

36. GregLTurnquist.com/springone2020
Just do this…
6
● “Never delete a
column”

37. GregLTurnquist.com/springone2020
Just do this…
6
● “Never delete a
column”
● Handle new
clients

38. GregLTurnquist.com/springone2020
Just do this…
6
● “Never delete a
column”
● Handle new
clients
● Support old
clients

39. GregLTurnquist.com/springone2020
Just do this…
6
● “Never delete a
column”
● Handle new
clients
● Support old
clients
● Everyone wins!

40. GregLTurnquist.com/springone2020
What else do you need?

41. GregLTurnquist.com/springone2020
What else do you need?
● Hypermedia controls

42. GregLTurnquist.com/springone2020
What else do you need?
● Hypermedia controls
● Instead of telling someone how to use your API on a portal…

43. GregLTurnquist.com/springone2020
What else do you need?
● Hypermedia controls
● Instead of telling someone how to use your API on a portal…
● …give them the controls right in the API

44. GregLTurnquist.com/springone2020
What else do you need?
● Hypermedia controls
● Instead of telling someone how to use your API on a portal…
● …give them the controls right in the API
● …using standard media types

45. GregLTurnquist.com/springone2020
What else do you need?
● Hypermedia controls
● Instead of telling someone how to use your API on a portal…
● …give them the controls right in the API
● …using standard media types
● It’s how the web functions

46. GregLTurnquist.com/springone2020
What else do you need?
● Hypermedia controls
● Instead of telling someone how to use your API on a portal…
● …give them the controls right in the API
● …using standard media types
● It’s how the web functions
● It’s the reason the web succeeded

47. GregLTurnquist.com/springone2020
What else do you need?
● Hypermedia controls
● Instead of telling someone how to use your API on a portal…
● …give them the controls right in the API
● …using standard media types
● It’s how the web functions
● It’s the reason the web succeeded
● The reason everyone today builds web apps

48. GregLTurnquist.com/springone2020
Just migrate from this…
6

49. GregLTurnquist.com/springone2020
…to this!
6

50. GregLTurnquist.com/springone2020
…to this!
6

51. GregLTurnquist.com/springone2020
…to this!
6

52. GregLTurnquist.com/springone2020
…to this!
6

53. GregLTurnquist.com/springone2020
…to this!
6

54. GregLTurnquist.com/springone2020
…to this!
6

55. GregLTurnquist.com/springone2020
…to this!
6

56. GregLTurnquist.com/springone2020
…to this!
6

57. GregLTurnquist.com/springone2020
…to this!
6

58. GregLTurnquist.com/springone2020
{
"id": 0,
"firstName": "Frodo",
"lastName": "Baggins",
"role": "ring bearer",
"name": "Frodo Baggins",
"_links": {
"self": {
"href": "http://localhost:8080/rest/employees/0"
},
"employees": {
"href": "http://localhost:8080/rest/employees"
}
},
…
So you can do this!
6
● New clients

59. GregLTurnquist.com/springone2020
{
"id": 0,
"firstName": "Frodo",
"lastName": "Baggins",
"role": "ring bearer",
"name": "Frodo Baggins",
"_links": {
"self": {
"href": "http://localhost:8080/rest/employees/0"
},
"employees": {
"href": "http://localhost:8080/rest/employees"
}
},
…
So you can do this!
6
● New clients
● Old clients

60. GregLTurnquist.com/springone2020
{
"id": 0,
"firstName": "Frodo",
"lastName": "Baggins",
"role": "ring bearer",
"name": "Frodo Baggins",
"_links": {
"self": {
"href": "http://localhost:8080/rest/employees/0"
},
"employees": {
"href": "http://localhost:8080/rest/employees"
}
},
…
So you can do this!
6
● New clients
● Old clients
● Navigate between related
components

61. GregLTurnquist.com/springone2020
…and this
6
…
"_templates": {
"default": {
"method": "put",
"properties": [
{
"name": "firstName"
},
{
"name": "id",
"readOnly": true
},
{
"name": "lastName"
},
{
"name": "name"
},
{
"name": "role"
}
]}}}
● New clients
● Old clients
● Navigate between related
components
● Effect change

62. GregLTurnquist.com/springone2020
…
"_templates": {
"default": {
"method": "put",
"properties": [
{
"name": "firstName"
},
{
"name": "id",
"readOnly": true
},
{
"name": "lastName"
},
{
"name": "name"
},
{
"name": "role"
}
]}}}
…and this
6
● New clients
● Old clients
● Navigate between related
components
● Effect change

63. GregLTurnquist.com/springone2020
…
"_templates": {
"default": {
"method": "put",
"properties": [
{
"name": "firstName"
},
{
"name": "id",
"readOnly": true
},
{
"name": "lastName"
},
{
"name": "name"
},
{
"name": "role"
}
]}}}
…and this
6
● New clients
● Old clients
● Navigate between related
components
● Effect change (even for
old clients!)

64. GregLTurnquist.com/springone2020
Consuming Hypermedia

65. GregLTurnquist.com/springone2020
What if…

66. GregLTurnquist.com/springone2020
What if…
● You wanted your client to consume hypermedia?

67. GregLTurnquist.com/springone2020
What if…
● You wanted your client to consume hypermedia?
● Ready to register all those messy message converters?

68. GregLTurnquist.com/springone2020
What if…
● You wanted your client to consume hypermedia?
● Ready to register all those messy message converters?
● Do you really want to look up how to customize RestTemplate (or
WebClient) to handle HAL, HAL-FORMS, etc., etc., etc.?

69. GregLTurnquist.com/springone2020
What if…
● You wanted your client to consume hypermedia?
● Ready to register all those messy message converters?
● Do you really want to look up how to customize RestTemplate (or
WebClient) to handle HAL, HAL-FORMS, etc., etc., etc.?

70. GregLTurnquist.com/springone2020
What if…
● You wanted your client to consume hypermedia?
● Ready to register all those messy message converters?
● Do you really want to look up how to customize RestTemplate (or
WebClient) to handle HAL, HAL-FORMS, etc., etc., etc.?
Spring HATEOAS has you covered!

71. GregLTurnquist.com/springone2020
RestTemplate support

72. GregLTurnquist.com/springone2020
RestTemplate support

73. GregLTurnquist.com/springone2020
RestTemplate support

74. GregLTurnquist.com/springone2020
RestTemplate support

75. GregLTurnquist.com/springone2020
RestTemplate support

76. GregLTurnquist.com/springone2020
We also support WebClient
● Inject WebClient.Builder into your app
● …and .build()!

77. GregLTurnquist.com/springone2020
We also support WebClient
● Inject WebClient.Builder into your app
● …and .build()!

78. GregLTurnquist.com/springone2020
We also support WebClient

79. GregLTurnquist.com/springone2020
We also support WebClient

80. GregLTurnquist.com/springone2020
We also support WebClient

81. GregLTurnquist.com/springone2020
We also support WebClient
😳Not in production!

82. GregLTurnquist.com/springone2020
Additional Features

83. GregLTurnquist.com/springone2020
Additional Features
● Spring WebFlux support

84. GregLTurnquist.com/springone2020
Additional Features
● Spring WebFlux support
● More media types (UBER+JSON, Collection+JSON, Your Own ™)

85. GregLTurnquist.com/springone2020
Additional Features
● Spring WebFlux support
● More media types (UBER+JSON, Collection+JSON, Your Own ™)
● Standardized errors with Problem+JSON (RFC-7807)

86. GregLTurnquist.com/springone2020
Additional Features
● Spring WebFlux support
● More media types (UBER+JSON, Collection+JSON, Your Own ™)
● Standardized errors with Problem+JSON (RFC-7807)
● Lots of performance improvements

87. GregLTurnquist.com/springone2020
Additional Features
● Spring WebFlux support
● More media types (UBER+JSON, Collection+JSON, Your Own ™)
● Standardized errors with Problem+JSON (RFC-7807)
● Lots of performance improvements
● Increasing community involvement
● JSON:API, Siren media types
● Document updates
● New ideas!

88. GregLTurnquist.com/springone2020
Additional Features
● Spring WebFlux support
● More media types (UBER+JSON, Collection+JSON, Your Own ™)
● Standardized errors with Problem+JSON (RFC-7807)
● Lots of performance improvements
● Increasing community involvement
● JSON:API, Siren media types
● Document updates
● New ideas!

89. GregLTurnquist.com/springone2020
Additional Features
● Spring WebFlux support
● More media types (UBER+JSON, Collection+JSON, Your Own ™)
● Standardized errors with Problem+JSON (RFC-7807)
● Lots of performance improvements
● Increasing community involvement
● JSON:API, Siren media types
● Document updates
● New ideas!

90. GregLTurnquist.com/springone2020
Additional Features
● Spring WebFlux support
● More media types (UBER+JSON, Collection+JSON, Your Own ™)
● Standardized errors with Problem+JSON (RFC-7807)
● Lots of performance improvements
● Increasing community involvement
● JSON:API, Siren media types
● Document updates
● New ideas!
Check it out!

91. GregLTurnquist.com/springone2020
Thank you SpringOne 2020!
Join me on #session-building-flexible-apis-with-spring-hateoas
for Q&A
Follow us on twitter @SpringHATEOAS
Visit GregLTurnquist.com/springone2020 to WIN a
paperback+ebook copy of Hacking with Spring Boot 2.3