Java@NotBlank

Java @NotBlank is a validation constraint used in Java programming language to check if a given string is not blank or empty. It is a part of the Java Bean Validation API and is commonly used to validate user inputs in web applications.

To use the @NotBlank constraint, you need to add the following import statement to your Java class:

import javax.validation.constraints.NotBlank;

Then, you can annotate your string field or parameter with the @NotBlank constraint as follows:

public class User {
    @NotBlank(message = "Username cannot be blank")
    private String username;
    
    public User(String username) {
        this.username = username;
    }
    
    // ...
}

In this example, the @NotBlank constraint is used to ensure that the username field is not blank or empty. If the username is blank, a validation error message "Username cannot be blank" will be returned.

Note that the @NotBlank constraint only checks for blank or empty strings, not for null values. If you need to check for null values as well, you can use the @NotNull constraint.