I recently had a look into Spring Validation and discovered new ways it can be used. Here's a simple example that is commonly used in Spring Boot applications.
A simple Person class with validation constraint annotations:
package com.example.spring_validated.lib;
import jakarta.validation.constraints.Min;
import jakarta.validation.constraints.NotBlank;
public class Person {
@NotBlank
private String name;
@Min(18)
private int age;
public Person(String name, int age) {
this.name = name;
this.age = age;
}
}
And a controller that uses the Person class as a dependency:
package com.example.spring_validated;
import com.example.spring_validated.lib.Person;
import jakarta.validation.Valid;
import org.springframework.validation.annotation.Validated;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RestController;
@RestController
@Validated
public class PersonController {
@PostMapping("/person")
public String createPerson(@Valid @RequestBody Person person) {
return "Person created: " + person.getName();
}
}
If we use this endpoint without giving a name in the request body, we will get a 400 Bad Request response since it does not meet the constraints in the Person class.
In my application, the Person class is declared in a separate library, meaning that Spring Validation actually works across different libraries. Additionally, not only will Spring Validation apply constraints from your dependency class, but it also works with sub-dependencies as long as they are annotated with @Valid, like this Address record:
package com.example.spring_validated.anotherlib;
import jakarta.validation.constraints.NotBlank;
public record Address(@NotBlank String street) {}
package com.example.spring_validated.lib;
import com.example.spring_validated.anotherlib.Address;
import jakarta.validation.constraints.Min;
import jakarta.validation.constraints.NotBlank;
public class Person {
@NotBlank
private String name;
@Min(18)
private int age;
@NotNull
@Valid
private Address address;
public Person(String name, int age) {
this.name = name;
this.age = age;
}
}
My investigation was led by a desire to validate outside a controller, and I found that @Validated can also be applied to other beans like Services.
package com.example.spring_validated.app;
import org.springframework.stereotype.Service;
import org.springframework.validation.annotation.Validated;
import com.example.spring_validated.lib.Person;
import jakarta.validation.Valid;
@Service
@Validated
public class PersonService {
public void validate(@Valid Person person) {
System.out.println("Validated person: " + person);
}
}
This is useful in my case where I want to validate data classes that we formed via extensive business logic before it is persisted or sent to another service.
I found some new ways to apply validations in my applications and I hope you can too.
