java 47 lines · 7 steps

Polymorphic payment requests in Spring

A Spring REST endpoint deserializes and validates one of several payment types using a sealed interface and Jackson subtype resolution.

Explained by highlit

Spring Advanced polymorphic deserialization sealed interfaces bean validation records rest api

1@RestController
2@RequestMapping("/api/payments")
3public class PaymentController {
4 
  private final PaymentProcessor processor;
6 
  public PaymentController(PaymentProcessor processor) {
      this.processor = processor;
  }
10 
  @PostMapping
  public ResponseEntity<PaymentReceipt> submit(@Valid @RequestBody PaymentRequest request) {
      PaymentReceipt receipt = processor.charge(request);
      return ResponseEntity.status(HttpStatus.CREATED).body(receipt);
  }
16 
  @JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.EXISTING_PROPERTY, property = "method", visible = true)
  @JsonSubTypes({
      @JsonSubTypes.Type(value = CardPayment.class, name = "card"),
      @JsonSubTypes.Type(value = BankTransferPayment.class, name = "bank_transfer"),
      @JsonSubTypes.Type(value = WalletPayment.class, name = "wallet")
  })
  public sealed interface PaymentRequest permits CardPayment, BankTransferPayment, WalletPayment {
      String method();
      long amountCents();
  }
27 
  public record CardPayment(
          @NotNull String method,
          @Positive long amountCents,
          @NotBlank @Pattern(regexp = "\\d{16}") String cardNumber,
          @NotBlank String expiry) implements PaymentRequest {
  }
34 
  public record BankTransferPayment(
          @NotNull String method,
          @Positive long amountCents,
          @NotBlank String iban,
          @NotBlank String accountHolder) implements PaymentRequest {
  }
41 
  public record WalletPayment(
          @NotNull String method,
          @Positive long amountCents,
          @NotBlank String walletId) implements PaymentRequest {
  }
47}

01 / 01

STEP 01

Walkthrough

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Three takeaways

1A sealed interface with Jackson subtypes lets one endpoint accept several concrete shapes while keeping the type set closed and exhaustive.
2Records make immutable DTOs concise, and validation annotations on their components enforce per-type rules automatically.
3Combining @Valid with polymorphic binding means each incoming payment method is validated against only its own constraints.

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