@RequestParam vs @RequestBody — Query String vs JSON Body

Direct Answer

@RequestParam binds request parameters such as query-string or form values. @RequestBody reads the request body through an HttpMessageConverter. The body is not necessarily JSON and query parameters are not limited to GET. Choose from the API contract: filters/options often fit query parameters, while a structured create/update command commonly belongs in the body.

Code Example

@RestController
@RequestMapping("/api/products")
public class ProductController {

    // @RequestParam: extracts from query string
    @GetMapping
    public List<Product> search(
            @RequestParam String category,
            @RequestParam(defaultValue = "0") int page,
            @RequestParam(defaultValue = "20") int size) {
        // Called via: GET /api/products?category=electronics&page=0&size=20
        return productService.findByCategory(category, page, size);
    }

    // @RequestBody: extracts from request body (JSON payload)
    @PostMapping
    public Product create(@RequestBody CreateProductRequest request) {
        // Called via: POST /api/products with JSON body:
        // {"name":"Laptop","price":999.99,"category":"electronics"}
        return productService.create(request);
    }
}

record CreateProductRequest(String name, double price, String category) {}

Common Mistakes & Pitfalls

• Using @RequestParam for complex objects: Freshers sometimes try to pass a whole User object as query params like ?name=John&email=john@example.com&age=25. This works for tiny objects but becomes unmaintainable and hits URL length limits. Complex objects should go in @RequestBody as JSON.
• Forgetting @RequestParam is required by default: If a query param is missing, Spring throws an error unless you add required = false or provide a defaultValue. Freshers often forget this and get confusing 400 Bad Request errors.
• Using @RequestBody with GET requests: HTTP GET requests typically don't have a body (some clients ignore it). If you need to send complex criteria for a search, either use POST for the search endpoint or flatten the params into query strings with multiple @RequestParam annotations.