REST is a stateless protocol. It is designed on grails 3.0.0. Since it is stateless protocol so unable to manage session.

1. •REST Api using Grails

2. Agenda
✔ What is REST service
✔ Guidelines to create REST Api
✔ Domain class as REST resource
✔ Implementing REST Controller
✔ Customizing Response Rendering
✔ Versioning REST Resources

3. What is REST service
✔ Service:- App that is hosted in backend and ready to
serve data
✔ REST is stand for (Representational State Transfer)

4. Guidelines to create REST Api
✔ Use HTTP methods (Client will request data with
http)
✔ Expose directory structure like URIs
✔ Transfer XML or JSON (Javascript Object Notation)
or both
✔ Be stateless. (server does not store any state about
the client session on the server side.)

5. REST is very simple and involves
• XML, JSON as a communication medium
• Combined with URL parameters
• Use HTTP methods GET, POST, PUT, DELETE

6. Each HTTP method maps to an action type
• GET:- retrieving data
• POST:- creating data
• PUT:- updating data
• DELETE:- Delete data

7. Domain classes as REST resources
• Expose a domain class as a REST resource. It can be done by adding grails.rest.Resource @Resource
• Specify a URI@Resource(uri = '/persons')
• Now domain is available as a REST resource either JSON or XML formats. Default type is XML.
• Ex:-
• package com
• import grails.rest.Resource
• @Resource(uri = '/persons')
• class Person {
• static constraints = {
• }
• }

8. Header Information
● Content Type
● Accept

9. • package com
• import
grails.rest.Resource
• @Resource(uri =
'/persons')
• class Person {
• String firstName
• String lastName
• Long age
• static constraints = {
• }
• <person id="1">
• <age>25</age>
• <firstName>Vijay</firstNa
me>
• <lastName>Shukla</lastN
ame>
• </person>

10. • <list>
• <person id="1">
• <age>25</age>
• <firstName>Vijay</firstNa
me>
• <lastName>Shukla</last
Name>
• </person>
• <person id="2">
• <age>30</age>
• [{"class":"com.Person"
,"id":1,"age":25,"firstN
ame":"Vijay","lastNam
e":"Shukla"},{"class":"c
om.Person","id":2,"ag
e":30,"firstName":"Kar
an","lastName":"Aah

11. •If you want to change the defult representation from
XML to JSON then
•add formats option like:-
•@Resource(uri = '/persons', formats = ['json', 'xml'])

12. • [{"class":"com.Person","i
d":1,"age":25,"firstName
":"Vijay","lastName":"Sh
ukla"},{"class":"com.Per
son","id":2,"age":30,"first
Name":"Karan","lastNa
me":"Aahuja"}]
• Instead of using the file
extension in the URI,
you can also obtain a
JSON response using
the ACCEPT header.
• curl -i -H "Accept:
application/json"

13. You can create a new resource by issuing
a POST request:
• curl -i -X POST -H "Content-Type: application/json" -d
'{"firstName":"Testing", "lastName":"REST",
"age":"85"}'
• HTTP/1.1 201 Created
• Server: Apache-Coyote/1.1
• X-Application-Context:
application:development
• Location:
http://localhost:8080/persons/3

14. When any Error Occured then
• curl -i -X POST -H "Content-Type: application/json" -d
'{"firstName":"Testing"}' http://localhost:8080/persons
• HTTP/1.1 422 Unprocessable Entity
• Server: Apache-Coyote/1.1
• X-Application-Context: application:development
• Content-Type: application/json;charset=UTF-8
• Transfer-Encoding: chunked
• Date: Sun, 10 Jan 2016 03:32:48 GMT
• {"errors":[{"object":"com.Person","field":"age","r

15. Updating can be done with a PUT request:
• curl -i -X PUT -H "Content-Type: application/json" -d
'{"firstName":"Testing", "lastName":"Renaming", "age":"05"}'
• Response:-
• HTTP/1.1 200 OK
• Server: Apache-Coyote/1.1
• X-Application-Context: application:development
• Location: http://localhost:8080/persons/1
• Content-Type: application/json;charset=UTF-8
• Transfer-Encoding: chunked
• Date: Sat, 09 Jan 2016 14:06:10 GMT
• {"class":"com.Person","id":1,"age":5,"firstName":"Testing","lastName":"Rena
ming"}
• Now by hitting

16. If you not provide any ID to be update by PUT
• curl -i -X PUT -H "Content-Type: application/json" -d
'{"firstName":"Testing", "lastName":"Renaming", "age":"05"}'
http://localhost:8080/persons
• HTTP/1.1 405 Method Not Allowed
• Server: Apache-Coyote/1.1
• X-Application-Context: application:development
• Allow: GET, HEAD
• Content-Type: application/json;charset=UTF-8
• Transfer-Encoding: chunked
• Date: Sun, 10 Jan 2016 03:35:27 GMT
• {"timestamp":1452396927350,"status":405,"error":"Method Not
Allowed","exception":"org.springframework.web.HttpRequestM
ethodNotSupportedException","message":"Request method

17. a resource can be deleted with DELETE request:
• curl -i -X DELETE -H "Content-Type: application/json"
• Response:- HTTP/1.1 204 No Content
• Server: Apache-Coyote/1.1
• X-Application-Context: application:development
• Date: Sat, 09 Jan 2016 14:08:35 GMT
• Now, by hitting
• [{"class":"com.Person","id":2,"age":30,"firstName":"Karan","lastName
":"Aahuja"},{"class":"com.Person","id":3,"age":85,"firstName":"Testing
","lastName":"REST"}]

18. If the data you want to delete is not available
• curl: (6) Could not resolve host: Content-Type
• HTTP/1.1 404 Not Found
• Server: Apache-Coyote/1.1
• X-Application-Context: application:development
• Content-Length: 0
• Date: Sat, 09 Jan 2016 14:10:07 GMT

19. Update only one field:-
• curl -X PATCH -H "Content-Type: application/json" -d
'{"firstName":"REST API TESTING"}'
http://localhost:8080/persons/2• {"class":"com.Person","id":2,"age":30,"firstName":"REST API
TESTING","lastName":"Aahuja"}
• Now hitting
• [{"class":"com.Person","id":1,"age":25,"firstName":"Vijay","lastN
ame":"Shukla"},{"class":"com.Person","id":2,"age":30,"firstNam
e":"REST API TESTING","lastName":"Aahuja"}]

20. •We can enable read-only capabilities ny setting reaadOnly attribute to
true:-
•@Resource(uri='/books', readOnly=true)
•In this case POST, PUT and DELETE requests will be forbidden.
•package com
•import grails.rest.Resource
•@Resource(uri = '/persons', formats = ['json', 'xml'], readOnly = true)
•class Person {
• String firstName
• String lastName
• Long age
• static constraints = {
• }
•}

21. • curl -i -H "Accept:
application/json"
http://localhost:8080/persons
• HTTP/1.1 200 OK
• Server: Apache-Coyote/1.1
• X-Application-Context:
application:development
• Content-Type:
application/json;charset=UTF
-8
• Transfer-Encoding: chunked
• Date: Sat, 09 Jan 2016
14:15:05 GMT
• [{"class":"com.Person","id":1,"
• curl -i -X POST -H
"Content-Type:
application/json" -d
'{"firstName":"DO NOT",
"lastName":"ENTER",
"age":"85"}'
http://localhost:8080/per
sons
• HTTP/1.1 405 Method
Not Allowed
• Server: Apache-
Coyote/1.1
• X-Application-Context:
application:development
• Content-Length: 0
• Date: Sat, 09 Jan 2016
• If you have done any changes then refresh your application
else you may get this error
• curl -i -H "Accept: application/json"
http://localhost:8080/persons
• curl: (7) Failed to connect to localhost port 8080: Connection

22. •If you prefer to keep all url part in UrlMapping then simply
remove uri part from domain and below line in UrlMapping.groovy
•"/persons"(resources:"person")
•Ex:-
•import grails.rest.Resource
•@Resource(formats = ['json', 'xml'], readOnly = true)
•class Person {
• String firstName
• String lastName
• Long age
• static constraints = {
• }
•}

23. Works Done by Resource Annotation
✔ Automatic Mappings
✔ No Controllers created
✔ UrlMappiings.groovy not updated
✔ HTTP status codes
✔ HTTP methods

24. REST-ful Controller
• Create domain
• Create controller/ Generate Controller
• Add this line to URLMppings.groovy
• "/companies"(controller: "company", action: "index",
method: "GET")
• "/companies"(controller: "company", action: "save",
method: "POST")
• "/companies/$id"(controller: "company", action:
"update", method: "PUT")
• "/companies/$id"(controller: "company", action:
"patch", method: "PATCH")

25. ✔ Controller Class must extends RestfulController
✔ Add static response formats
✔ class CompanyController extends RestfulController {
✔ static responseFormats = ["json", "xml"]
✔ CompanyController() {
✔ super(Company)
✔ }
✔ }

26. URL MAPPING REPORTS
✔ HTTP Methods
✔via mappings
✔“/custom”(controller=”custom”, action=”index”,
method=”GET”)
✔via controllers
✔static allowedMethods = [sav:”POST”,
update:”PUT”]
✔ Either use allowedMethod way or mapping ways

27. Default Media Types
✔ xml if nothing specified
✔ on mappings and controllers
✔formats = [“json”,”xml”]
✔ Extension
✔/countries.xml
✔/countries.json
✔ Requesting a format not included returns 406 Not Acceptable

28. Custom Response Renderer
• Register custom JSON or XML renderers bean in
resources.groovy
• beans = {
• countryJsonRenderer(JsonCollectionRenderer,
Country) {
• excludes = ['abreviation']
• }
• personJsonRenderer(XmlCollectionRenderer,
Person){
• excludes = ["age"]
• }

29. Custom Response Renderer
• Registeriing Custome Renderer in Bootstrap.grroovy
• JSON.registerObjectMarshaller(Country) {
• return [
• id : it.id,
• countryName : it.countryName,
• abbreviation: it.abbreviation,
• continent : it.continent
• ]
• }

30. References