RESTful API, which stands for Representational State Transfer, is an architectural
style for designing networked applications. It was introduced by Roy Fielding in
his doctoral dissertation in 2000. REST is not a standard but rather a set of
principles and constraints that, when followed, guide the design of scalable and
maintainable web services.
Key principles and characteristics of a RESTful API include:
1. **Statelessness:** Each request from a client to a server must contain all the
information needed to understand and fulfill the request. The server should not
store any information about the client's state between requests. This enhances
scalability and simplifies the design.
2. **Client-Server Architecture:** Separation of concerns between the client and
the server. The client is responsible for the user interface and user experience,
while the server is responsible for processing requests, managing resources, and
handling business logic.
3. **Uniform Interface:** A uniform and consistent way of interacting with
resources (entities or services) is provided. This includes:
- **Resource Identification:** Resources are uniquely identified by URIs
(Uniform Resource Identifiers).
- **Resource Manipulation through Representations:** Resources can be
manipulated using representations (such as JSON or XML) that the client
understands.
- **Self-Descriptive Messages:** Each message from the server to the client
includes enough information for the client to understand and process the response.
- **Hypermedia as the Engine of Application State (HATEOAS):** The server
includes hypermedia links in the response, allowing the client to navigate the
application's state dynamically.
4. **Stateless Communication:** Communication between the client and server is
stateless, meaning that each request from the client to the server must contain all
the information necessary for the server to understand and fulfill the request. The
server does not store any client state between requests.
5. **Resource-Based:** Resources are the key abstractions in REST, representing
entities or services. Resources are identified by URIs, and interactions are
performed using standard HTTP methods (GET, POST, PUT, DELETE) to manipulate the
resources.
6. **Stateless Server:** The server does not store any information about the state
of the client. Each request from the client must contain all the information needed
for the server to fulfill the request.
7. **Cacheability:** Responses from the server can be explicitly marked as
cacheable or non-cacheable to improve performance and reduce the load on the
server.
RESTful APIs are widely used in web development because of their simplicity,
scalability, and compatibility with the HTTP protocol. They are commonly used to
build web services that can be consumed by various clients, including web browsers,
mobile devices, and other applications. The adoption of RESTful principles has led
to the development of RESTful web services that are widely used in modern software
architecture.