API, short for Application Programming Interface, acts as a bridge between different software applications. It establishes rules and tools allowing these applications to communicate with each other. In essence, APIs define how software systems can interact without needing to know the internal workings of one another.
Types of APIs
Web APIs (or Web Services): These are accessed over the internet using standard web protocols like HTTP. They facilitate communication between web servers and client applications.
Library APIs: These are sets of functions and procedures that allow developers to create software applications more efficiently by providing pre-written code for common tasks.
OS APIs: Operating System APIs provide functions and procedures for programmers to utilize the capabilities of the underlying operating system.
RESTful APIs and REST Guidelines
REST, or Representational State Transfer, is an architectural style for designing networked applications. RESTful APIs adhere to REST principles, using standard HTTP methods (GET, POST, PUT, DELETE) for communication. They are designed to be stateless, scalable, and easy to understand.
Key Concepts:
Resources: These are entities or concepts that can be identified and manipulated over the web, such as students, employees, or products. Each resource is uniquely identified by a URI.
HTTP Methods: APIs define operations to manipulate resources, including GET (retrieve), POST (create), PUT (update), and DELETE (delete).
JSON: Representing data in JSON format (key-value pairs) is common in RESTful APIs for data exchange.
Stateless: Each client-server request contains all necessary information, and the server does not store client state between requests.
Designing Action-Centric APIs
While traditional REST APIs focus on resources, it's possible to design APIs centered around actions or operations. Here are some tips:
Identify Operations: Clearly define the actions you want to expose through your API.
Use Nouns for Actions: Represent actions with nouns in your URI paths (e.g., /calculations instead of /calculate).
Choose HTTP Methods: Decide on appropriate HTTP methods for your actions, considering POST for most operations.
Document Clearly: Provide comprehensive documentation specifying available actions, parameters, and response formats.
Consider Security: Implement proper authentication and authorization mechanisms for your API, depending on the nature of actions.
Annotations for Working with APIs
@Controller: Marks a class as a controller component in Spring MVC.
@ResponseBody: Indicates that the return value of a method should be serialized directly to the HTTP response body.
@RestController: Combines @Controller and @ResponseBody, simplifying RESTful API development.
@RequestParam: Binds parameters from the request to method parameters in Spring MVC.
@RequestBody: Binds the body of a web request to method parameters in Spring MVC.
@GetMapping, @PostMapping: Maps HTTP GET and POST requests to handler methods.
@RequestMapping: Maps HTTP requests to handler methods, providing more flexibility in URI mapping.
@PathVariable: Extracts values from the URI path in Spring MVC.
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