What is REST API? A RESTful Tutorial

Since the World Wide access of the internet, we have been using different applications and websites to get data for various resources. However, have you ever thought, where does this data come from? Well, it’s the servers from where we get the data. So in this article on What is REST API, let us look into how a client communicates with the servers to get the required information.

What is REST

REST is acronym for REpresentational State Transfer. It is architectural style for distributed hypermedia systems and was first presented by Roy Fielding in 2000 in his famous dissertation.

REST suggests to create an object of the data requested by the client and send the values of the object in response to the user. For example, if the user is requesting for a movie in Noida at a certain place and time, then you can create an object on the server-side.

So, over here, you have an object and you are sending the state of an object. This is why REST is known as Representational State Transfer.

If I have to define REST, then, Representational State Transfer a.k.a REST is an architectural style as well as an approach for communications purpose that is often used in various web services development.

The architectural style of REST helps in leveraging the lesser use of bandwidth to make an application more suitable for the internet. It is often regarded as the “language of the internet” and is completely based on the resources.

Need of REST API

Consider a scenario where you are using the Movie Ticket Booking app. Now, obviously, this application needs a lot of Input data, as the data present in the application is never static. Either it is movies getting released on a frequent basis, or various cities showing different languages movies at various times of the day. It’s never static which implies the fact that data is always changing in these applications.

Now, where do you think we get this data from?

Well, this data is received from the Server or most commonly known as a Web-server. So, the client requests the server for the required information, via an API, and then, the server sends a response to the client.

The data returned by the server, in response to the request of the client is either in the format of JSON or XML. Both JSON and XML formats have a proper hierarchical structure of data.

But, the only issue which is present in this framework until now is that you have to use a lot of methods to get the required information. To the fact, using these methods to retrieve information, becomes quite cumbersome when you require complex data.

So, this is where REST API comes into the picture. The REST API creates an object, and thereafter sends the values of an object in response to the client. It breaks down a transaction in order to create small modules. Now, each of these modules is used to address a specific part of the transaction. This approach provides more flexibility but requires a lot of effort to be built from the very scratch.

Like any other architectural style, REST also does have it’s own 6 guiding constraints which must be satisfied if an interface needs to be referred as RESTful. These principles are listed below.

Guiding Principles of REST

Client–server – By separating the user interface concerns from the data storage concerns, we improve the portability of the user interface across multiple platforms and improve scalability by simplifying the server components.
Stateless – Each request from client to server must contain all of the information necessary to understand the request, and cannot take advantage of any stored context on the server. Session state is therefore kept entirely on the client.
Cacheable – Cache constraints require that the data within a response to a request be implicitly or explicitly labeled as cacheable or non-cacheable. If a response is cacheable, then a client cache is given the right to reuse that response data for later, equivalent requests.
Uniform interface – By applying the software engineering principle of generality to the component interface, the overall system architecture is simplified and the visibility of interactions is improved. In order to obtain a uniform interface, multiple architectural constraints are needed to guide the behavior of components. REST is defined by four interface constraints: identification of resources; manipulation of resources through representations; self-descriptive messages; and, hypermedia as the engine of application state.
Layered system – The layered system style allows an architecture to be composed of hierarchical layers by constraining component behavior such that each component cannot “see” beyond the immediate layer with which they are interacting.
Code on demand (optional) – REST allows client functionality to be extended by downloading and executing code in the form of applets or scripts. This simplifies clients by reducing the number of features required to be pre-implemented.

Methods of REST API

HTTP Verb	CRUD	Entire Collection (e.g. /customers)	Specific Item (e.g. /customers/{id})
POST	Create	201 (Created), ‘Location’ header with link to /customers/{id} containing new ID	404 (Not Found), 409 (Conflict) if resource already exists.
GET	Read	200 (OK), list of customers. Use pagination, sorting and filtering to navigate big lists.	200 (OK), single customer. 404 (Not Found), if ID not found or invalid
PUT	Update/Replace	405 (Method Not Allowed), unless you want to update/replace every resource in the entire collection	200 (OK) or 204 (No Content). 404 (Not Found), if ID not found or invalid
PATCH	Update/Modify	405 (Method Not Allowed), unless you want to modify the collection itself	200 (OK) or 204 (No Content). 404 (Not Found), if ID not found or invalid
DELETE	Delete	405 (Method Not Allowed), unless you want to delete the whole collection—not often desirable	200 (OK). 404 (Not Found), if ID not found or invalid

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