@NotNull is not validating and not Producing correct Result in Spring Framework

Question

I have created a simple Application that checks whether the given first name and lastname is null or not . i have used @NotNull annotation to check

The code for the Student.java is

    @NotNull(message = "Name must not be null")
    private String firstName;
    @NotNull(message = "Name must not be null")
    private String lastName;

i have also created StudentController.java

 public String processForm(@Valid @ModelAttribute("student") Student student,BindingResult bindingResult)
{
    //bindingResult is not an annotation
    if(bindingResult.hasErrors())
    {
        return "error";
    }
    else
    {
        return "success";
    }
}

My HTML Form is

<br/>
<form:input path="firstName"/>
<form:input path="lastName"/>
<br/>

i havent given value for firstName and the lastName , and i have submitted the form. The form redirects to "success" page which is incorrect.

My pom.xml file is

<?xml version="1.0" encoding="UTF-8"?>

http://maven.apache.org/xsd/maven-4.0.0.xsd"> 4.0.0

<groupId>org.sample.mvc</groupId>
<artifactId>formspringmvc</artifactId>
<version>1.0-SNAPSHOT</version>
<packaging>war</packaging>

<dependencies>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-webmvc</artifactId>
        <version>4.3.12.RELEASE</version>
    </dependency>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-beans</artifactId>
        <version>4.3.12.RELEASE</version>
    </dependency>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-context</artifactId>
        <version>4.3.12.RELEASE</version>
    </dependency>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-web</artifactId>
        <version>4.3.12.RELEASE</version>
    </dependency>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-core</artifactId>
        <version>4.3.12.RELEASE</version>
    </dependency>
    <dependency>
        <groupId>javax.servlet</groupId>
        <artifactId>javax.servlet-api</artifactId>
        <version>3.1.0</version>
    </dependency>

    <dependency>
        <groupId>javax.servlet.jsp</groupId>
        <artifactId>jsp-api</artifactId>
        <version>2.1</version>
    </dependency>

    <dependency>
        <groupId>javax.validation</groupId>
        <artifactId>validation-api</artifactId>
        <version>1.1.0.Final</version>
    </dependency>

    <dependency>
        <groupId>javax.servlet</groupId>
        <artifactId>jstl</artifactId>
        <version>1.2</version>
    </dependency>
</dependencies>

Answer 1

When you submit the form, String fields are posted as empty but not null. Here are some more constraints you can use:

@NotNull

String cannot be null, however can be empty.

@NotEmpty

String cannot be null and not empty (size > 0).

@NotBlank

String cannot be null and must contain at least one non-whitespace character.

String firstName = null;

// @NotNull: false
// @NotEmpty: false
// @NotBlank: false

---

String firstName = "";

// @NotNull: true
// @NotEmpty: false
// @NotBlank: false

---

String firstName = " ";

// @NotNull: true
// @NotEmpty: true
// @NotBlank: false

---

String firstName = "er-han";

// @NotNull: true
// @NotEmpty: true
// @NotBlank: true