Difference between jakarta.validation-api & spring-boot-starter-validation

 

🔹 1. jakarta.validation-api

This provides the standard interface (API) for bean validation.
It includes annotations like:

@NotNull
@Size(min = 3, max = 10)
@Email
@Min(1)
@Max(100)

Dependency:

<dependency>
  <groupId>jakarta.validation</groupId>
  <artifactId>jakarta.validation-api</artifactId>
</dependency>

🔸 But: this is only the API, not the implementation.
You still need something to run these validations (see below).

---

🔹 2. spring-boot-starter-validation

This is a Spring Boot starter that:

• Automatically includes the jakarta.validation-api

• Adds the actual implementation (Hibernate Validator)

• Integrates validation into Spring Boot (like @Valid in controllers)

Dependency:

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

---

✅ So Which One Should You Use?

You should only use:

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

Because:

• It already includes jakarta.validation-api

• It also brings in Hibernate Validator

• Works perfectly with Spring Boot MVC / REST with @Valid

---

✨ Example in Spring Boot:

public class UserDTO {
    @NotNull
    @Size(min = 3, max = 20)
    private String name;

    @Email
    private String email;
}

In controller:

@PostMapping("/user")
public ResponseEntity<String> createUser
(@Valid @RequestBody UserDTO userDto) {
    return ResponseEntity.ok("Valid user!");
}


-----------------Difference----------


🎯 Use in Real Projects
In Spring Boot apps, always use:

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

It brings:
Jakarta API (@NotNull, etc.)
Hibernate Validator engine
Spring integration (works with @Valid in controllers)



🧠 Tricky Interview Q&A
1. Q: If I only add jakarta.validation-api to my pom.xml, will validation work?
👉 A: No, because jakarta.validation-api only provides interfaces and annotations. 
You still need an implementation (like Hibernate Validator).

2. Q: What's the benefit of using spring-boot-starter-validation over directly 
adding jakarta.validation-api and Hibernate Validator?
👉 A: spring-boot-starter-validation bundles everything you need and 
auto-configures it for Spring Boot. Less config, more productivity.

3. Q: Can I use Jakarta Validation in non-Spring Java applications?
👉 A: Yes, but you must manually include both jakarta.validation-api and 
an implementation like Hibernate Validator.

4. Q: What happens behind the scenes when I annotate a DTO with @Valid 
in Spring Boot?
👉 A: Spring uses the Hibernate Validator (from the starter) to validate the 
fields based on annotations. If validation fails, 
a MethodArgumentNotValidException is thrown and handled globally.

5. Q: Which validation provider is included by default in Spring Boot 
Starter Validation?
👉 A: Hibernate Validator.

Happy Learning... :)