What is REST? What are RESTful Web Services?

What is REST? What are RESTful Web Services?

This tutorial provides an introduction to RESTful web services and goes over what REST is as well as HTTP.

REST stands for REpresentational State Transfer. It is a popular architectural approach to create your API's in today's world.

You Will Learn
  • What is REST?
  • What are the fundamentals of REST APIs?
  • How do you make use of HTTP when building REST API?
  • What is a Resource?
  • How do you identify REST API Resources?
  • What are some of the best practices in designing REST API?
What Is REST?

The acronym REST stands for REpresentational State Transfer. It was term originally coined by Roy Fielding, who was also the inventor of the HTTP protocol. The striking feature of REST services is that they want to make the best use of HTTP. Let's now have a quick overview of HTTP.

A Relook at HTTP

Let's open up the browser and visit a web page first:

And then click on one of the result pages:

Next, we can click on the link on the page we end up in:

And land upon another page:

This is how we typically browse the web.

When we browse the internet, there are a lot of things that happen behind the scenes. The following is a simplified view of what happens between the browser, and the servers running on the visited websites:

The HTTP Protocol

When you enter a URL such as https://www.google.com in the browser, a request is sent to the server on the website identified by the URL. That server then responds with a response. The important thing is the formats of these requests and responses. These formats are defined by a protocol called HTTPHyper Text Transfer Protocol.

When you type in a URL at the browser, it sends out a GET request to the identified server. The server then replies with an HTTP response that contains data in HTMLHyper Text Markup Language. The browser then takes this HTML and displays it on your screen.

Let's say you are filling in a form present on a web page with a list of details. In such a scenario when you click the Submit button, an HTTP POST request gets sent out to the server.

HTTP and RESTful Web Services

HTTP provides the base layer for building web services. Therefore, it is important to understand HTTP. Here are a few key abstractions.

Resource

A resource is a key abstraction that HTTP centers round. A resource is anything you want to expose to the outside world through your application. For instance, if we write a todo management application, instances of resources are:

  • A specific user
  • A specific todo
  • A list of todos

Resource URIs

When you develop RESTful services, you need to focus your thinking on the resources in the application. The way we identify a resource to expose, is to assign a URIUniform Resource Identifier — to it. For example:

  • The URI for the user Ranga is /user/ranga
  • The URI for all the todos belonging to Ranga is /user/Ranga/todos
  • The URI for the first todo that Ranga has is /user/Ranga/todos/1

Resource Representation

REST does not worry about how you represent your resource. It could be XML, HTML, JSON, or something entirely different! The only important thing is you clearly define your resource and perform whatever actions that are supported on it by making use of features already provided by HTTP. Examples are:

  • Create a user: POST /users
  • Delete a user: DELETE /users/1
  • Get all users: GET /users
  • Get a single user: GET /users/1
REST and Resources

A significant point to note is that with REST, you need to think about your application in terms of resources:

  • Identify what resources you want to expose to the outside world
  • Make use of the verbs already specified by HTTP to perform operations on these resources

Here is how a REST service is generally implemented:

  • Data Exchange Format: No restriction is imposed over here. JSON is a highly popular format, although other such as XML can be used as well
  • Transport: Always HTTP. REST is completely built on top of HTTP.
  • Service Definition: There is no standard to specify this, and REST is flexible. This could be a drawback in some scenarios, as it might be necessary for the consuming application to understand the request and response formats. There are widely used ones however, such as WADL (Web Application Definition Language) and Swagger.

REST focuses on resources and how effectively you perform operations on them using HTTP.

The Components of HTTP

HTTP defines the following for a request:

For the response, HTTP defines the:

HTTP Request Methods

The method used in a HTTP request indicates what action you want to perform with that request. Important examples are:

  • GET: Retrieve details of a resource
  • POST : Create a new resource
  • PUT: Update an existing resource
  • DELETE: Delete a resource

HTTP Response Status Code

A status code is always present in a HTTP response. Common examples are:

  • 200: Success
  • 404: Page not found
Summary

In this article, we had a high-level look at REST. We stressed the fact that HTTP is the building block of REST services. HTTP is a protocol that is used to define the structure of browser requests and responses. We saw that HTTP deals mainly with resources that are exposed on web servers. Resources are identified using URIs, and operations on these resources are performed using verbs defined by HTTP.

Finally, we looked at how REST services make the best use of features offered by HTTP to expose resources to the outside world. REST does not put any restrictions on the resource representation formats or on the service definition.

What is REST API? | Restful Web Service

What is REST API? | Restful Web Service

In this post "Restful Web Service", you'll learn: What is Web services, what is API, What is REST API, How REST works and Implementation of REST API

What is REST API? | Restful Web Service

A REST API defines a set of functions to process requests and responses via HTTP protocol.

REST is used in mobile application as well as in web applications.


What the difference between REST API and RESTful API?

What the difference between REST API and RESTful API?

Representational state transfer (REST) is a style of software architecture. As described in a dissertation by Roy Fielding, REST is an "architectural style" that basically exploits the existing technology and protocols of the Web. RESTful is typically used to refer to web services implementing such an architecture.

The short answer is that REST stands for Representational State Transfer. It’s an architectural pattern for creating web services. A RESTful service is one that implements that pattern.

The long answer starts with “sort of” and “it depends” and continues with more complete definitions.

Defining REST

Let’s start by defining what REST is and is not. For some, REST means a server that exchanges JSON documents with a client over HTTP. Not only is that not a complete definition, but it’s also not always true. The REST specification doesn’t require HTTP or JSON. (The spec doesn’t mention JSON or XML at all.)

The Origins of REST

Roy Fielding introduced the REST architectural pattern in a dissertation he wrote in 2000. The paper defines a means for clients and servers to exchange application data. A key feature is that the client doesn’t need to know anything about the application in advance. The link is to chapter five of his paper. While the entire dissertation describes the hows and whys of REST, that chapter defines the architectural pattern.

Fielding doesn’t mandate specific requirements. Instead, he defines REST regarding constraints and architectural elements.

REST’s Architectural Constraints

Here is a summary of the constraints.

  • Client-server – REST applications have a server that manages application data and state. The server communicates with a client that handles the user interactions. A clear separation of concerns divides the two components. This means you can update and improve them in independent tracks.
  • Stateless – servers don’t maintain any client state. Clients manage their application state. Their requests to servers contain all the information required to process them.
  • Cacheable – servers must mark their responses as cacheable or not. So, infrastructures and clients can cache them when possible to improve performance. They can dispose of non-cacheable Information, so no client uses stale data.
  • Uniform interface – this constraint is REST’s most well known feature or rule, depending on who you ask. Fielding says “The central feature that distinguishes the REST architectural style from other network-based styles is its emphasis on a uniform interface between components.” REST services provide data as resources, with a consistent namespace. We’ll cover this in detail below.
  • Layered system – components in the system cannot “see” beyond their layer. So, you can easily add load-balancers and proxies to improve security or performance.

A RESTful service is more than a web server that exchanges JSON, or any other, documents. These constraints work together to create a very specific type of application.

Applying the Constraints

First, the client-server, layered systems and stateless constraints combine to form an application with solid boundaries and clear separations between concerns. Data moves from the server to the client upon request. The client displays or manipulates it. If the state changes, the client sends it back to the server for storage. Fielding specifically contrasts REST with architectures that use distributed objects to hide data from other components. In REST, the client and server share knowledge about data and state. The architecture doesn’t conceal data, it only hides implementations.

The cacheable and uniform state constraints go one step further. Application data is available to clients in a clear and consistent interface and cached when possible.

So, that’s the technical definition of REST. What does it look like in the real world?

RPC Over HTTP vs. RESTful

Often when someone says that a service “isn’t REST,” they’re looking at the URIs or how the service uses HTTP verbs. They’re referring to REST’s presentation of data as a uniform set of resources.

This distinction is sometimes framed as a difference between remote procedures calls (RPC) and REST. Imagine a web service for listing, adding, and removing, items from an e-commerce inventory.

In one version, there’s a single URL that we query with HTTP GETs or POSTs.  You interact with the service by POSTing a document, setting the contents to reflect what you want to do.

Add new items with a POST with a NewItem:

POST /inventory HTTP/1.1
 
{
    "NewItem": {
          "name": "new item",
          "price": "9.99",
          "id": "1001"
      }
}    

Query for items with a POST and an ItemRequest:

POST /inventory HTTP/1.1
 
{
    "ItemRequest": {
          "id": "1001"
      }
}

Some implementations accept a request for a new item with a get, too.

POST /inventory?id=1001 HTTP/1.1

We also change or delete items with a POST and an ItemDelete or ItemUpdate.

POST /inventory HTTP/1.1
 
{
    "ItemDelete": {
          "id": "1001"
      }
}

This isn’t REST. We’re not exchanging the state of resources. We’re calling a function with arguments that happen to be in a JSON document or URL arguments.

A RESTful service has a URI for each item in the inventory.

So, adding a new item would look like the example above.

POST /item HTTP/1.1
 
{
    "Item": {
          "name": "new item",
          "price": "9.99",
          "id": "1001"
      }
}    

But the similarities end there. Retrieving an item is always a GET:

GET /item/1001 HTTP/1.1   

Deleting is a DELETE:

DELETE /item/1001 HTTP/1.1  

Modifying an item is a PUT:

POST /inventory HTTP/1.1
 
{
    "Item": {
          "name": "new item",
          "price": "7.99",
          "id": "1001"
      }
}    

The difference is important. In REST, operations that use distinct HTTP actions. These verbs correspond directly to the activity on the data. GET, POST, PUT, DELETE and PATCH all have specific contracts. Most well-designed REST APIs also return specific HTTP codes, depending on the result of the request.

The critical point is that the URIs operate on the data, not on remote methods.

But there’s another reason why the resource model is essential.

REST vs RESTful and the Richardson Maturity Model

When you model your URIs after resources and use HTTP verbs you make your API predictable. Once developers know how you defined your resources, they can almost predict what the API looks like. Here again, the emphasis is on understanding the data, not the operations.

But even if you can’t make the API entirely predictable, you can document any REST service with hypertext. So, each item returned in the inventory app would contain links for deleting, modifying, or setting the inventory level of the resource. Fielding says that before a service is RESTful, it must provide hypertext media as part of the API.

Many sites don’t meet this requirement but are still called REST. Fact is, many sites break the rules in one way or another. So many that Leonard Richardson created a model breaks down REST into levels of compliance

We’ve already covered the source levels:

  • 0 – exporting an API over HTTP with methods called with arguments
  • 1 – Exporting resources instead of methods
  • 2 – Proper use of HTTP verbs
  • 3 – Exporting hypertext with objects that make all or part of the API discoverable.

Richardson’s model is his own, and it doesn’t map directly into Fielding’s spec. Since Fielding requires level three, he would say that most apps aren’t REST anyway.

The point is many services that we colloquially refer to as REST, technically aren’t.

REST vs RESTful: Does It Matter?

So, does the REST vs. RESTful comparison matter? Probably not. How well your architecture complies with an arbitrary standard isn’t as important with how well it suits your needs and can grow with your business.

The REST architectural pattern has many advantages. Fielding designed it for the web and, 18 years later, most of the constraints he had in mind are still with us. In 2000 we didn’t have Android or the iPhone. IE5 had 50% of the browser market share. It’s biggest rival was Firefox. But Fielding recognized what online applications needed and how web clients would evolve from HTML display engines into complete applications. The tools we use today have grown to suit REST, not the other way around.

Thank you for reading. Hope this tutorial will help you!

What the difference between REST API and RESTful API?

What the difference between REST API and RESTful API?

Representational state transfer (REST) is a style of software architecture. As described in a dissertation by Roy Fielding, REST is an "architectural style" that basically exploits the existing technology and protocols of the Web. RESTful is typically used to refer to web services implementing such an architecture.

The short answer is that REST stands for Representational State Transfer. It’s an architectural pattern for creating web services. A RESTful service is one that implements that pattern.

The long answer starts with “sort of” and “it depends” and continues with more complete definitions.

Defining REST

Let’s start by defining what REST is and is not. For some, REST means a server that exchanges JSON documents with a client over HTTP. Not only is that not a complete definition, but it’s also not always true. The REST specification doesn’t require HTTP or JSON. (The spec doesn’t mention JSON or XML at all.)

The Origins of REST

Roy Fielding introduced the REST architectural pattern in a dissertation he wrote in 2000. The paper defines a means for clients and servers to exchange application data. A key feature is that the client doesn’t need to know anything about the application in advance. The link is to chapter five of his paper. While the entire dissertation describes the hows and whys of REST, that chapter defines the architectural pattern.

Fielding doesn’t mandate specific requirements. Instead, he defines REST regarding constraints and architectural elements.

REST’s Architectural Constraints

Here is a summary of the constraints.

  • Client-server – REST applications have a server that manages application data and state. The server communicates with a client that handles the user interactions. A clear separation of concerns divides the two components. This means you can update and improve them in independent tracks.
  • Stateless – servers don’t maintain any client state. Clients manage their application state. Their requests to servers contain all the information required to process them.
  • Cacheable – servers must mark their responses as cacheable or not. So, infrastructures and clients can cache them when possible to improve performance. They can dispose of non-cacheable Information, so no client uses stale data.
  • Uniform interface – this constraint is REST’s most well known feature or rule, depending on who you ask. Fielding says “The central feature that distinguishes the REST architectural style from other network-based styles is its emphasis on a uniform interface between components.” REST services provide data as resources, with a consistent namespace. We’ll cover this in detail below.
  • Layered system – components in the system cannot “see” beyond their layer. So, you can easily add load-balancers and proxies to improve security or performance.

A RESTful service is more than a web server that exchanges JSON, or any other, documents. These constraints work together to create a very specific type of application.

Applying the Constraints

First, the client-server, layered systems and stateless constraints combine to form an application with solid boundaries and clear separations between concerns. Data moves from the server to the client upon request. The client displays or manipulates it. If the state changes, the client sends it back to the server for storage. Fielding specifically contrasts REST with architectures that use distributed objects to hide data from other components. In REST, the client and server share knowledge about data and state. The architecture doesn’t conceal data, it only hides implementations.

The cacheable and uniform state constraints go one step further. Application data is available to clients in a clear and consistent interface and cached when possible.

So, that’s the technical definition of REST. What does it look like in the real world?

RPC Over HTTP vs. RESTful

Often when someone says that a service “isn’t REST,” they’re looking at the URIs or how the service uses HTTP verbs. They’re referring to REST’s presentation of data as a uniform set of resources.

This distinction is sometimes framed as a difference between remote procedures calls (RPC) and REST. Imagine a web service for listing, adding, and removing, items from an e-commerce inventory.

In one version, there’s a single URL that we query with HTTP GETs or POSTs.  You interact with the service by POSTing a document, setting the contents to reflect what you want to do.

Add new items with a POST with a NewItem:

POST /inventory HTTP/1.1
 
{
    "NewItem": {
          "name": "new item",
          "price": "9.99",
          "id": "1001"
      }
}    

Query for items with a POST and an ItemRequest:

POST /inventory HTTP/1.1
 
{
    "ItemRequest": {
          "id": "1001"
      }
}

Some implementations accept a request for a new item with a get, too.

POST /inventory?id=1001 HTTP/1.1

We also change or delete items with a POST and an ItemDelete or ItemUpdate.

POST /inventory HTTP/1.1
 
{
    "ItemDelete": {
          "id": "1001"
      }
}

This isn’t REST. We’re not exchanging the state of resources. We’re calling a function with arguments that happen to be in a JSON document or URL arguments.

A RESTful service has a URI for each item in the inventory.

So, adding a new item would look like the example above.

POST /item HTTP/1.1
 
{
    "Item": {
          "name": "new item",
          "price": "9.99",
          "id": "1001"
      }
}    

But the similarities end there. Retrieving an item is always a GET:

GET /item/1001 HTTP/1.1   

Deleting is a DELETE:

DELETE /item/1001 HTTP/1.1  

Modifying an item is a PUT:

POST /inventory HTTP/1.1
 
{
    "Item": {
          "name": "new item",
          "price": "7.99",
          "id": "1001"
      }
}    

The difference is important. In REST, operations that use distinct HTTP actions. These verbs correspond directly to the activity on the data. GET, POST, PUT, DELETE and PATCH all have specific contracts. Most well-designed REST APIs also return specific HTTP codes, depending on the result of the request.

The critical point is that the URIs operate on the data, not on remote methods.

But there’s another reason why the resource model is essential.

REST vs RESTful and the Richardson Maturity Model

When you model your URIs after resources and use HTTP verbs you make your API predictable. Once developers know how you defined your resources, they can almost predict what the API looks like. Here again, the emphasis is on understanding the data, not the operations.

But even if you can’t make the API entirely predictable, you can document any REST service with hypertext. So, each item returned in the inventory app would contain links for deleting, modifying, or setting the inventory level of the resource. Fielding says that before a service is RESTful, it must provide hypertext media as part of the API.

Many sites don’t meet this requirement but are still called REST. Fact is, many sites break the rules in one way or another. So many that Leonard Richardson created a model breaks down REST into levels of compliance

We’ve already covered the source levels:

  • 0 – exporting an API over HTTP with methods called with arguments
  • 1 – Exporting resources instead of methods
  • 2 – Proper use of HTTP verbs
  • 3 – Exporting hypertext with objects that make all or part of the API discoverable.

Richardson’s model is his own, and it doesn’t map directly into Fielding’s spec. Since Fielding requires level three, he would say that most apps aren’t REST anyway.

The point is many services that we colloquially refer to as REST, technically aren’t.

REST vs RESTful: Does It Matter?

So, does the REST vs. RESTful comparison matter? Probably not. How well your architecture complies with an arbitrary standard isn’t as important with how well it suits your needs and can grow with your business.

The REST architectural pattern has many advantages. Fielding designed it for the web and, 18 years later, most of the constraints he had in mind are still with us. In 2000 we didn’t have Android or the iPhone. IE5 had 50% of the browser market share. It’s biggest rival was Firefox. But Fielding recognized what online applications needed and how web clients would evolve from HTML display engines into complete applications. The tools we use today have grown to suit REST, not the other way around.

Thank you for reading. Hope this tutorial will help you!