@RequestParam in Spring MVC — Query String Parameter Binding

Direct Answer

@RequestParam binds request parameters, commonly from the query string, to a handler argument. It is required by default unless a default value, Optional, or required=false changes that contract. Use query parameters for filters, search, sorting, pagination, and other request options; they can also appear in form-encoded requests.

Code Example

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

    private final UserRepository userRepository;

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

    @GetMapping
    public List<User> searchUsers(
            @RequestParam(required = false) String status,
            @RequestParam(required = false) String email,
            @RequestParam(defaultValue = "0") int page,
            @RequestParam(defaultValue = "20") int size) {
        // GET /api/users?status=ACTIVE&page=2&size=10
        // status and email are optional (null if not provided)
        // page defaults to 0, size defaults to 20
        return userRepository.findUsers(status, email, page, size);
    }

    @GetMapping("/search")
    public List<User> searchByName(
            @RequestParam String name,  // required: returns 400 if missing
            @RequestParam(defaultValue = "ASC") String sortOrder) {
        return userRepository.findByNameContaining(name, sortOrder);
    }
}

Common Mistakes & Pitfalls

• Making all params required: Freshers write @RequestParam String status without required=false, so clients must always provide every parameter or get a 400 error. This breaks flexibility — optional filters should be optional. Use required=false or defaultValue to avoid this.
• Forgetting type conversion errors: If a client sends page=abc and your parameter is int, Spring throws MethodArgumentTypeMismatchException. Freshers don't handle this with an exception handler, returning a confusing 500 instead of a clear 400.
• Not using defaultValue for pagination: Writing @RequestParam int page without a default means clients must always specify page numbers. Use defaultValue="0" so GET /users works without query params and still returns the first page.