@PathVariable in Spring MVC — Extracting URL Path Segments

Direct Answer

@PathVariable binds a value captured from a request-mapping URI template. For @GetMapping("/users/{id}"), a request to /users/42 binds id to 42 and Spring converts it to the declared parameter type. Path variables commonly identify resources, but route design—not the annotation—decides their business meaning.

Code Example

@RestController
@RequestMapping("/api/users")
public class UserController {

    private final UserRepository userRepository;

    public UserController(UserRepository userRepository) {
        this.userRepository = userRepository;
    }

    @GetMapping("/{userId}")
    public User getUserById(@PathVariable Long userId) {
        // Spring extracts userId from /api/users/42 -> userId = 42
        return userRepository.findById(userId)
            .orElseThrow(() -> new ResourceNotFoundException("User not found"));
    }

    @GetMapping("/{userId}/orders/{orderId}")
    public Order getUserOrder(@PathVariable Long userId, 
                              @PathVariable Long orderId) {
        // Multiple path variables: /api/users/10/orders/250
        return userRepository.findOrderByUserAndId(userId, orderId)
            .orElseThrow(() -> new ResourceNotFoundException("Order not found"));
    }
}

Common Mistakes & Pitfalls

• Using @RequestParam for resource IDs: Freshers often write @GetMapping("/users") with @RequestParam Long id, resulting in /users?id=42 instead of the RESTful /users/42. This breaks REST conventions and makes URLs harder to read and cache.
• Forgetting type conversion errors: If a client sends /users/abc where abc can't convert to Long, Spring throws MethodArgumentTypeMismatchException. Freshers forget to handle this with @ExceptionHandler and return a proper 400 Bad Request.
• Naming mismatches: When the path variable name differs from the parameter name, you must specify it: @PathVariable("userId") Long id. Freshers forget the annotation parameter and get binding errors.