REST Architecture with use case and example

REST(Representational State Transfer)
- SHAILESH SINGH

1. Why so REST FUL?
 Life before REST
 Challenges of HTTP ?
 RMI , SOAP , RPC and HTTP different famous technique to develop web services

2. What is REST? Defined in 2000
 Architects are Made, Not Born
 What REST father Roy Fielding says
 An architecture style is a coordinated set of architectural constraints that restricts the
roles and features of architectural elements . E.g. : UI layer and data layer segregation ,
statelessness , cacheability
 Uniform Interface : Overall system architecture is simplified and the visibility of
interactions is improved
Tradeoff : Degrades efficiency since Information is transferred in a standardised form
rather than one which is specific to application's needs

a. Uniform Interface
 Four interface constraints
● Identification of resources
● Manipulation of resources through representations
● Self descriptive messages
● Hypermedia as the engine of application state (HATEOAS)

b. What is resources
Another way to describe REST is ROA : Resource Oriented Architecture
 Any information that can be named is a resource
 A resource is a conceptual mapping to a set of entities not the entity itself. Such a
mapping can change over time.
 A resource can be a collection of entities too.
 Every resource has a name that uniquely identifies it – the URI
 Think of it like a primary key for each row in a database
 REST doesn't dictate URI choice. Leaves it to the application author.

c.What If?
/getAccount
/getAllAccounts
/searchAccounts
/createDirectory
/updateGroup
/updateGroupName
/findGroupsByDirectory
/verifyAccountEmailAddress
As you move from an action oriented design towards resource oriented design,
thinking of everything as nouns is one of the early challenges to overcome

d.The Answer
Fundamentally two types of resources:
Collection Resource
/applications
/books
/orders
Instance Resource
/applications/a1b2c3
/books/1235
/orders/abcdef
Question :
Guess REST equivalent for : Transaction.approve and Account.pay
TransactionApproval and AccountPayment

e.Behavior
POST, GET, PUT, DELETE
≠ 1:1
Create, Read, Update, Delete

f. PUT for Create
Identifier is known by the client:
PUT:
Used to create a resource, or overwrite it. While you specify the resources new URL.
For a new resource:
PUT /questions/<new_question> HTTP/1.1
Host: www.example.com/
To overwrite an existing resource:
PUT /questions/<existing_question> HTTP/1.1
PUT is Idempotent

g.POST as Create
 POST:
Used to modify and update a resource
POST /questions/<existing_question> HTTP/1.1
Note that the following is an error:
POST /questions/<new_question> HTTP/1.1
If the URL is not yet created, you should not be using POST to create it while specifying the name. This should result in a 'resource not found'
error because <new question> does not exist yet. You should PUT the <new question> resource on the server first.
You could though do something like this to create a resources using POST:
POST /applications
{
“name”: “Best App Ever”
}
Response:
201 Created
Location: https://api.singh.com/applications/a1b2c3
POST NOT Idempotent -> x++ vs. x=4

4.a. Example/case Studies
 Fine grained CRUD resources Vs Coarse Grained resources:
Like Operation on blog post (“/posts/{post_id}/likes”)
Comment Operation on blog post (“/posts/{post_id}/comments”)
vs
The single coarse grained resource “Post”(/posts/{post_id}” for “liking” or
“commenting”

4.b. Example/case Studies
 Change the Address:
We can update “Customer” address via “Customers/001/Address/KA001/” or
“Address/KA001/”
VS
Design the API around the resources that are based on the business processes and domain events . To
update an existing bank customer’s address, a POST request can be made to “ChangeOfAddress” resource.
Very important to distinguish between resources in REST API and domain entities in a
domain driven design.

4.c HATEOAS
 HATEOAS=Hypermedia As The Engine Of Application State
Path is the hierarchical and the query is the non-hierarchical part of the URIs.
! Magic awesome sauce to improve REST!
According to the HATEOAS constraint your client has to follow hyperlinks sent by
the service. Those hyperlinks must be annotated with metadata regarding the
semantics of them

HATEOAS constrain
 A REST client enters a REST application through a simple fixed URL. All future actions the client may take are discovered within resource representations
returned from the server.
 E.g:
Request
GET /account/12345
HTTP/1.1 Host: somebank.org
Accept: application/xml
Response:
HTTP/1.1 200 OK
Content-Type: application/xml
Content-Length: ...
<?xml version="1.0"?>
<account>
<account_number>12345</account_number>
<balance currency="usd">100.00</balance>
<link rel="deposit" href="https://somebank.org/account/12345/deposit" />
<link rel="withdraw" href="https://somebank.org/account/12345/withdraw" />
<link rel="transfer" href="https://somebank.org/account/12345/transfer" />
<link rel="close" href="https://somebank.org/account/12345/close" />
</account>
Later Response:
HTTP/1.1 200 OK
Content-Type: application/xml
Content-Length: ...
<?xml version="1.0"?>
<account>
<account_number>12345</account_number>
<balance currency="usd">-25.00</balance>
<link rel="deposit" href="https://somebank.org/account/12345/deposit" />
</account>

Worked examples
How to GET a Cup of Coffee by Jim Webber, Savas
Parastatidis & Ian Robinson Oct 02, 2008
http://www.infoq.com/articles/webber-rest-workflow

Questions
http://petstore.swagger.io/
http://start.spring.io/

REST Architecture with use case and example

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