Understanding the @RequestMapping Annotation in Spring MVC

What does @RequestMapping annotation?

The @RequestMapping annotation in Spring Framework is used to map web requests to specific handler methods in a controller. It is a versatile annotation that can be applied at both the class and method levels to define the URL patterns that a particular controller or method should handle.

Key Features of @RequestMapping:

1. Mapping URLs: You can specify the URL patterns that the method or class should respond to. For example:

   @RequestMapping("/hello")
   public String sayHello() {
       return "Hello, World!";
   }
   

2. HTTP Methods: You can specify which HTTP methods (GET, POST, PUT, DELETE, etc.) the mapping should respond to using the method attribute:

   @RequestMapping(value = "/submit", method = RequestMethod.POST)
   public String submitForm() {
       return "Form submitted!";
   }
   

3. Request Parameters: You can also map requests based on specific request parameters using the params attribute:

   @RequestMapping(value = "/greet", params = "name")
   public String greet(@RequestParam String name) {
       return "Hello, " + name + "!";
   }
   

4. Content Types: The consumes and produces attributes allow you to specify the content types that the method can consume or produce:

   @RequestMapping(value = "/json", consumes = "application/json", produces = "application/json")
   public ResponseEntity<MyResponse> handleJson(@RequestBody MyRequest request) {
       // Handle JSON request
   }
   

5. Path Variables: You can use path variables in the URL mapping:

   @RequestMapping("/users/{id}")
   public User getUser(@PathVariable String id) {
       return userService.findById(id);
   }
   

6. Class-Level and Method-Level Annotations: You can use @RequestMapping at the class level to define a base URL for all methods in the controller:

   @RequestMapping("/api")
   public class ApiController {
       @RequestMapping("/users")
       public List<User> getUsers() {
           // Return list of users
       }
   }
   

Example Usage:

Here’s a simple example of a Spring controller using @RequestMapping:

import org.springframework.web.bind.annotation.*;

@RestController
@RequestMapping("/api")
public class MyController {

    @GetMapping("/hello")
    public String hello() {
        return "Hello, World!";
    }

    @PostMapping("/submit")
    public String submit(@RequestBody String data) {
        return "Data submitted: " + data;
    }

    @GetMapping("/users/{id}")
    public User getUser(@PathVariable String id) {
        return userService.findById(id);
    }
}

Conclusion:

The @RequestMapping annotation is a powerful tool in Spring MVC for handling web requests. It provides a flexible way to define how different HTTP requests are routed to specific methods in your controllers, allowing for the creation of RESTful web services and web applications.