Category: java
Spring Boot validation
Published on 06 Apr 2026
Explanation
Spring Boot field validation ensures
incoming request
data is correct before processing.
It helps
prevent invalid input such as empty fields,
wrong email format, or short passwords.
Code:
// Add dependency (Maven) <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-validation </artifactId> </dependency>
Explanation
Validation annotations are added inside
DTO classes
to define rules like required fields,
email
format, or minimum length.
Code:
import jakarta.validation.constraints.*;
public class StudentDTO {
@NotBlank(message = "Name is required")
private String name;
@Email(message = "Invalid email format")
private String email;
@Size(min = 6, message = "Password
must be at least 6 characters")
private String password;
}
Explanation
@Valid annotation is used in controller
methods
to trigger validation automatically
when request data
is received.
Code:
import org.springframework.web.
bind.annotation.*;
import jakarta.validation.Valid;
@RestController
@RequestMapping("/students")
public class StudentController {
@PostMapping
public String createStudent(
@Valid @RequestBody StudentDTO studentDTO) {
return "Student created
successfully";
}
}
Explanation
Common validation annotations include
@NotNull, @NotBlank, @Email,
@Size, @Min, and @Max to enforce input
constraints.
Code:
public class UserDTO {
@NotNull(message = "ID cannot be null")
private Long id;
@NotBlank(message = "Username required")
private String username;
@Min(value = 18,
message = "Minimum age is 18")
private int age;
}
Explanation
Validation errors can be captured using
BindingResult
to return custom error messages instead of
default responses.
Code:
import org.springframework.
validation.BindingResult;
@PostMapping("/register")
public Object registerUser(@Valid
@RequestBody
UserDTO userDTO, BindingResult result) {
if(result.hasErrors()) {
return result.getAllErrors();
}
return "User registered successfully";
}
Explanation
Field validation improves API reliability
and security
by preventing invalid or incomplete data
from
entering backend systems such as student
registration
or certificate workflows in training
platforms 🎓.
Code:
@NotBlank(message = "Course name required") private String courseName;