Validation Package

Here's a step-by-step explanation of Java Spring validation using the Bean Validation framework:

Add Dependencies: Ensure that you have the necessary dependencies in your project. Spring Boot projects typically include the spring-boot-starter-validation dependency, which automatically adds the required validation libraries.

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

Annotate Model Classes: Add validation annotations to the fields of your model classes. These annotations are provided by the javax.validation.constraints package. Common annotations include @NotNull, @NotEmpty, @Size, @Min, @Max, etc.

public class User {
    @NotNull
    @Size(min = 5, max = 30, message = "The length of the customer name should be between 5 and 30")  
	private String name;

    @NotEmpty
    @Email
    private String email;

    // other fields and methods...
}

Controller Method with @Valid Annotation: In your controller methods, use the @Valid annotation to indicate that the input should be validated. This annotation can be applied to method parameters or request body objects.

@PostMapping("/users")
public ResponseEntity<String> createUser(@Valid @RequestBody User user) {
    // handle the valid user data
}