Spring Boot 4 Microservices & REST APIs · Lesson

Bean Validation with @Valid

Validate request bodies with annotations.

Bean Validation with @Valid is a free Spring Boot 4 Microservices & REST APIs lesson on CoddyKit — lesson 1 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Spring Boot 4 Microservices & REST APIs learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Bean Validation Overview

Bean Validation (JSR-380, Jakarta Validation) lets you declare constraints with annotations on your DTO fields, then validate objects against them. Spring Boot integrates it so incoming request bodies are checked automatically.

Adding the Dependency

The validation API plus an implementation (Hibernate Validator) come via the validation starter. Adding it activates annotation-driven validation in controllers.

<!-- pom.xml -->
<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-validation</artifactId>
</dependency>

Constraints on a DTO

Annotate fields with constraints. Each describes a rule the value must satisfy, plus an optional message shown when it fails.

public class CreateUserRequest {
    @NotBlank
    private String name;
    @Email @NotNull
    private String email;
    @Size(min = 8, max = 64)
    private String password;
    @Min(18)
    private int age;
    // getters/setters
}

Common Constraints

The standard annotations cover most needs:

@NotNull — value must not be null
@NotBlank — string must contain non-whitespace
@NotEmpty — collection/string not empty
@Size, @Min, @Max, @Email, @Pattern

Triggering Validation with @Valid

In a controller, annotate the request body parameter with @Valid. Spring validates it before your method body runs; on failure it short-circuits with an error.

@PostMapping("/users")
public ResponseEntity<Void> create(@Valid @RequestBody CreateUserRequest req) {
    userService.create(req);
    return ResponseEntity.status(HttpStatus.CREATED).build();
}

What Happens on Failure

If validation fails, Spring throws MethodArgumentNotValidException for a @RequestBody. By default this yields a 400 Bad Request, so invalid input never reaches your service layer.

Custom Messages

Override the default message per constraint with the message attribute, or externalize messages for i18n via a resource bundle.

@Size(min = 8, message = "Password must be at least 8 characters")
private String password;

Validating Path and Query Params

To validate individual method parameters (not a DTO), put constraints directly on them and add @Validated at the class level so method-level validation is active.

@Validated
@RestController
public class ProductController {
    @GetMapping("/products")
    public List<Product> list(@RequestParam @Min(1) int page) {
        return service.page(page);
    }
}

Nested Validation

Validation does not automatically descend into nested objects. Mark the nested field with @Valid so its constraints are also checked.

public class OrderRequest {
    @NotNull
    @Valid
    private AddressDto shippingAddress;
    // ...
}

Validating Collections

To validate each element of a collection, place @Valid on the collection field; each item’s constraints are then evaluated.

public class CartRequest {
    @NotEmpty
    private List<@Valid LineItem> items;
    // ...
}

Validation Groups

Validation groups let the same DTO enforce different rules in different contexts (for example create vs update). Annotate constraints with a group interface and validate against that group.

public interface OnCreate {}

public class UserDto {
    @Null(groups = OnCreate.class)
    private Long id; // must be null when creating
}

Quick Check

Test your understanding of @Valid.

Recap

Bean Validation guards your input.

Add spring-boot-starter-validation
Declare constraints like @NotBlank, @Size, @Email on DTOs
Trigger with @Valid on request bodies; failures yield 400
Use @Validated for param-level validation
Nested objects and collections need their own @Valid

Frequently asked questions

Is the “Bean Validation with @Valid” lesson free?

Yes — the full text of “Bean Validation with @Valid” is free to read here on the web, and the Spring Boot 4 Microservices & REST APIs course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Spring Boot 4 Microservices & REST APIs course, upgrade to CoddyKit PRO.

What will I learn in “Bean Validation with @Valid”?

Validate request bodies with annotations. You practise Spring Boot 4 Microservices & REST APIs with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Spring Boot 4 Microservices & REST APIs?

No prior experience is required. Spring Boot 4 Microservices & REST APIs on CoddyKit is structured for beginners through advanced learners; this is — lesson 1 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Bean Validation with @Valid” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Spring Boot 4 Microservices & REST APIs lesson?

Yes. Every Spring Boot 4 Microservices & REST APIs lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

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