Introduction to REST APIs
➢ Today I am going to talk about the term which you people heard a lot as
Rest APIs. REST states as Representational State Transfer (REST) and is an
architectural style that uses simple HTTP calls for inter-machine
communication instead of more complex options (RPC, SOAP).
➢ REST uses message-based communication and relies on the HTTP standard
to describe these messages. Using HTTP protocol means REST is a simple
Request/Response mechanism and each request returns a subsequent
response. The REST architecture uses 6 – key constraints as guidelines.
Client-Server: This model creates a uniform interface which separates clients
from Servers.
Stateless: protocol where no client context is stored on the server between
requests. Each request from any client contains all the information necessary to
service the request, and session state is held in the client.
Cacheable: Messages are enabled caching within the network path so
intermediate servers can cache the data for re-use.
Layered system: A client cannot tell whether it is connected directly to the end
server. This layered approach improves scalability, load balancing and shared
caching.
Uniform interface: The uniform interface simplifies and decouples the
architecture, which enables each part to evolve independently.
Code on demand: Is an optional constraint which allows permits Servers the
ability to extend.
Java applets and JavaScript as needed.
REST was built on the principles of HTTP and these Services can return types data
such as;
• XML
• JSON - (JavaScript Object Notation)
• HTML
• Plain Text
• Binary/octet (Images, PDF’s…)
What is HATEOAS and why is it important for REST API?
HATEOAS stands for Hypertext as The Engine of Application State. It means that
hypertext should be used to find a way through the API. Note the Server responds
with a "link" tag and URL needed to complete the specified action in the GET
method.
An example:
GET /account/12345 HTTP/1.1
HTTP/1.1 200 OK
<?xml version="1.0"?>
<account>
<account_number>12345</account_number>
<balance currency="usd">-25.00</balance>
<link rel="deposit" href="/account/12345/deposit" /> </account>
Why is REST popular?
➢ RESTful Web services are easily leveraged by most tools, including those
that are free and inexpensive. RESTful Services are less complex, more
efficient (use smaller message format) and provide better performance than
SOAP (Simple Operation Access Protocol).
➢ REST provides a lightweight architecture that promotes scalability and a
very loose coupling as it supports billions of users that are unaware of
network topology. In short REST is the architecture of the Web as it works
today and building Web Applications to use the architecture make a lot of
sense.
Benefits
• Extensibility
• Customizability
• Reusability
• Visibility
• Portability
• Reliability
Typical REST API calls:
HTTP is a Request/Response protocol. A client makes a Request to the Server and
the Server sends back a Response. The client builds a Request consisting of
Headers and Payload and Sends to a URL with an HTTP Method GET, PUT,
POST, HEAD, DELETE.
• GET – Retrieves a resource
• POST – Creates a resource
• PUT – Updates a resource
• DELETE – Deletes a resource
The Server builds a Response with Headers & Payload and sends it back to the
Client along with a status code validating the “response”.