Validating Composite Objects

Overview

A composite object refers to a structure where an object contains other objects as fields or includes collections (such as List, Set, Map) of objects.

• When validation is needed, it’s often necessary to validate not only individual fields but also such nested structures.
• Use @Valid

• @valid
  • Since @Valid propagates validation recursively, deeper nested structures can impact performance. It’s best to apply it only when necessary.
  • @Valid vs @Validated: For nested object validation itself, @Valid is sufficient; however, if you need additional features like group validation, use @Validated.

Example 1: User and Address

// Address.java
public class Address {
    @NotBlank(message = "City must not be blank")
    private String city;
 
    @Pattern(regexp = "\\d{5}", message = "Zip code must be 5 digits")
    private String zipCode;
 
    // getters and setters omitted
}

// User.java
public class User {
    @NotBlank(message = "Name must not be blank")
    private String name;
 
    @Valid  // Must be added on nested objects to trigger validation of inner fields
    private Address address;
 
    // getters and setters omitted
}

• Applying the @Valid annotation on the nested object field (Address address) triggers validation of the fields inside the Address object.
• Without @Valid, only the presence (e.g., null check) of the address field itself is validated in the User object, and internal fields like city and zipCode are ignored.

Example 2: Order and Product

// Product.java
public class Product {
    @NotBlank(message = "Product name must not be blank")
    private String name;
 
    @Positive(message = "Price must be greater than 0")
    private int price;
 
    // getters and setters omitted
}
 
// Order.java
public class Order {
    @NotBlank(message = "Customer is required")
    private String customer;
 
    @Valid  // Propagate validation to each element
    @Size(min = 1, message = "At least one product must be included")
    private List<Product> productList;
 
    // getters and setters omitted
}

• The @Valid annotation propagates validation to each element in a collection type (List, Set, Map, etc.).
• Constraints that apply to the collection as a whole (e.g., size restrictions) can be enforced using annotations like @Size.
• In this example, if productList is null or its size is 0, a validation error will occur.
• Additionally, each Product inside the list will be validated for its own constraints on name and price.