JSR 303 – Bean Validation – Nested Validation

Following up from my previous post about JSR 303 – Bean Validation, we will see how to apply it to any nested property and how to display validation error on screen using Spring MVC’s JSP tags

1. Bean Validation on Nested Property

Recall that to validate any property, we only need to put a Constraint annotation on top of its declaration. Example of common constraints are @NotEmpty, @Pattern, @Email. One thing in common of these constraints are that the applied property has to be of type String.

But if you have a bean called Person with an Address property and using these provided constraints, how do you validate that houseNumber, streetName are mandatory while country, province is not?

public class Person {
   @NotEmpty
   private String fullName;
 
   @Email
   private String email;
 
   @Pattern (regexp = "[0-9]+")
   private String telNo;
 
   @NotNull
   private Address address;
}
 
class Address {
   private String houseNumber;
 
   private String streetName;
 
   private String province;
 
   private String country;
}

You can create a custom constraint (e.g. @ValidAddress) – we will explore this option in the next post. Or you can use @Valid on the address property in combination of other constraints inside Address class. A valid example would be:

public class Person {
   @NotEmpty
   private String fullName;
 
   @Email
   private String email;
 
   @Pattern (regexp = "[0-9]+")
   private String telNo;
 
   @NotNull
   @Valid
   private Address address;
}
 
class Address {
   @NotEmpty
   private String houseNumber;
 
   @NotEmpty
   private String streetName;
 
   private String province;
 
   private String country;
}

@Valid constraint will instruct the Bean Validator to delve to the type of its applied property and validate all constraints found there. In above example, the validator, when seeing a @Valid constraint on address property, will explore the Address class and validate all JSR 303 Constraints found inside. Because houseNumber and streetName are marked with @NotEmpty constraints, they are mandatory; province and country on the other hand are optional.

2. Display Validation Error Using Spring MVC’s JSP Tags

Spring MVC tag library (<%@ taglib prefix=”form” uri=”[http://www.springframework.org/tags/form&#8221](http://www.springframework.org/tags/form&#8221); %>) offers a consistent way to display and collect input form. For our purpose, the tag used to display validation error is errors

Assume an instance of Person is an backing object of an input form and is displayed using Spring MVC tag.

Validation error on fullName field can be make visible by below code:

<form:errors path="fullName" />

Validation error on nested field such as houseNumber of address property can be make visible by specifying the full path:

<form:errors path="address.houseNumber" />