java 27 lines · 6 steps

Binding collection query params in Spring

A Spring REST endpoint maps repeated and comma-separated query parameters into typed collections and folds them into a filter.

Explained by highlit
Spring Intermediate rest-api query-parameters dependency-injection builder-pattern collections
1@RestController
2@RequestMapping("/api/products")
3public class ProductSearchController {
4 
5 private final ProductQueryService productQueryService;
6 
7 public ProductSearchController(ProductQueryService productQueryService) {
8 this.productQueryService = productQueryService;
9 }
10 
11 @GetMapping
12 public List<ProductView> search(
13 @RequestParam(name = "tags", required = false) List<String> tags,
14 @RequestParam(name = "ids", defaultValue = "") Set<Long> ids,
15 @RequestParam(name = "status", required = false) EnumSet<ProductStatus> statuses) {
16 
17 ProductFilter filter = ProductFilter.builder()
18 .tags(tags == null ? List.of() : tags)
19 .ids(ids)
20 .statuses(statuses == null ? EnumSet.allOf(ProductStatus.class) : statuses)
21 .build();
22 
23 return productQueryService.findMatching(filter).stream()
24 .map(ProductView::from)
25 .toList();
26 }
27}
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1Spring can bind a query parameter straight into a List, Set, or EnumSet, converting each element to the target type automatically.
  2. 2Defaulting absent optional parameters at the controller boundary keeps downstream services free of null checks.
  3. 3Mapping entities to view objects before returning keeps the API contract decoupled from the persistence model.

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