[FIXED] Why Notblank annotation displaying message?

Issue

I am working on spring mvc web application. In application, I put @NotBlank annotation for validation on username field in sign up form. I fill the username field and click on Submit button that time i get validation error message, but I fill username field so why BindingResult produce error behind username field and my @Size annotaion is not worked if insert less than 3 or greater than 12 character.

Here down is code:

Entity:

public class Registration {
    
    @NotBlank(message = "Username can not be empty !")
    @Size(min = 3, max = 12, message = "Username must be in 3 to 12 character") // Not working
    private String username;
    
    private String email;
    private Boolean agree;

    // constructor, getter, setter and toString()
}

Controller:

@GetMapping("/form")
public String formPage(Model mdl)
{
    mdl.addAttribute("registration", new Registration());
    return "form";
}
    
@PostMapping("/register")
public String registerUser(@Valid @ModelAttribute("registration") Registration registration, 
            BindingResult result)
{
    if(result.hasErrors())
    {
        System.out.println(result);
        return "form";
    }
        
    return "success";
}

form.html:

<form class="bg-white p-5" th:action="@{/register}" method="post" th:object="${registration}">
    <h1 class="text-center pt-2 pb-2">Signup Form</h1>
    <div class="mb-3">
        <label for="username" class="form-label">Username</label>
        <input type="text" 
            class="form-control"
            th:value="${registration.username}"
            id="username" />
        <p th:each="error : ${#fields.errors('username')}" th:text="${error}">
                        
        </p>
    </div>
    <div class="mb-3">
        <label for="email" class="form-label">Email address</label>
        <input type="text" 
            class="form-control"
            id="email"
            th:value="${registration.email}"
            aria-describedby="emailHelp" />
    </div>
    <div class="mb-3 form-check">
        <input type="checkbox" 
            class="form-check-input" 
            id="exampleCheck1">
        <label class="form-check-label" for="exampleCheck1">Check me out</label>
    </div>
    <button type="submit" class="btn btn-primary">Submit</button>
</form>

Xml for validation:

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

<dependency>
    <groupId>org.hibernate.validator</groupId>
    <artifactId>hibernate-validator</artifactId>
</dependency>

Snapshot of problem:

Solution

The problem is here

<input type="text" 
       class="form-control" 
       th:value="${registration.username}" 
       id="username"/>

You are missing the name attribute.

<input type="text" 
       class="form-control" 
       th:value="${registration.username}" 
       id="username" 
       name="username"/>

This will fix it.

The form normally is bound to an object - Registration in your case, using the name attributes of input tags. The annotations are working, the problem is that you are receiving null username in Registration due to that missing attribute.

Answered By - Chaosfire
Answer Checked By - David Marino (JavaFixing Volunteer)