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/verifyAccountEmailAddressAs you move from an action oriented design towards resource oriented design, thinking of everything as nouns is one of the early challenges to overcome

Identification of Resources

Identification of Resources

d.The AnswerFundamentally 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

≠ 1:1Create, 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

Host: www.example.com/

 PUT is Idempotent

g.POST as Create POST:Used to modify and update a resource

POST /questions/<existing_question> HTTP/1.1

Host: www.example.com/

Note that the following is an error:POST /questions/<new_question> HTTP/1.1Host: www.example.com/

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:

RequestGET /account/12345HTTP/1.1 Host: somebank.orgAccept: application/xml

Response:HTTP/1.1 200 OKContent-Type: application/xmlContent-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>

Book Flight Ticket

Get Flight Search Result

Confirm a Flight

Payment still Pending

Payment

Fetch E-Ticket

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/