Basic Spring Boot Controller Class Annotations

Overview of Dispatcher Servlet

When a user hits an API (e.g., a GET call to fetch a user), the Dispatcher Servlet uses Handler Mapping to identify the appropriate controller to handle the request.

Key Annotations for Handler Mapping

@Controller

Indicates that the class is responsible for handling incoming HTTP requests.

@RestController

Similar to @Controller, but it combines @Controller and @ResponseBody.

Difference Between @Controller and @RestController

@Controller requires @ResponseBody on each method, while @RestController automatically applies it to all methods.

Request Mapping

To map APIs to controller methods, we use the @RequestMapping annotation.

Example:

@RequestMapping("/api/v1")
public class SampleController {
    @GetMapping("/fetchUser ")
    public String getUser Details() {
        // Logic to fetch user details
    }
}

Simplified Mapping Annotations

@GetMapping and @PostMapping are shortcuts for @RequestMapping with specific HTTP methods.

Request Parameters

@RequestParam binds request parameters to method parameters.

@GetMapping("/fetchUser ")
public String getUser Details(@RequestParam String firstName, @RequestParam(required = false) String lastName) {
    // Logic to fetch user details
}

Type Conversion

Spring Boot automatically performs type conversion from request parameters to method parameter types.

Path Variables

@PathVariable is used to extract values from the URL path.

@GetMapping("/fetchUser /{id}")
public String getUser ById(@PathVariable String id) {
    // Logic to fetch user by ID
}

Request Body

@RequestBody binds the body of the HTTP request (typically JSON or XML) to a Java object.

@PostMapping("/saveUser ")
public ResponseEntity saveUser (@RequestBody User user) {
    // Logic to save user
}

Response Entity

ResponseEntity represents the entire HTTP response, including status, headers, and body.

@GetMapping("/fetchUser ")
public ResponseEntity getUser Details() {
    return ResponseEntity.ok("User  details fetched successfully");
}

Conclusion

In this session, we covered various annotations used in Spring Boot for handling HTTP requests and responses.