为什么方法级验证在Spring中不起作用?

学生班级:

package com.solvegen.education.student.enrollment.core.model;

import com.sun.istack.internal.NotNull;

import java.util.Date;

public class Student {
    private Long id;

    @NotNull
    private String userName;

    @NotNull
    private String firstName;

    @NotNull
    private String lastName;

    @NotNull
    private String password;

    @NotNull
    private String emailAddress;

    @NotNull
    private Date dateOfBirth;

    public Date getDateOfBirth() {
        return dateOfBirth;
    }

    public String getEmailAddress() {
        return emailAddress;
    }

    public String getFirstName() {
        return firstName;
    }

    public Long getId() {
        return id;
    }

    public String getLastName() {
        return lastName;
    }

    public String getPassword() {
        return password;
    }

    public String getUserName() {
        return userName;
    }

    public void setDateOfBirth(Date dateOfBirth) {
        this.dateOfBirth = dateOfBirth;
    }

    public void setEmailAddress(String emailAddress) {
        this.emailAddress = emailAddress;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

}

spring-config.xml的内容

<bean id="validator"
      class="org.springframework.validation.beanvalidation.LocalValidatorFactoryBean">
    <property name="providerClass" value="org.hibernate.validator.HibernateValidator"/>
</bean>
<bean id="validatorPostProcessor"
      class="org.springframework.validation.beanvalidation.MethodValidationPostProcessor">
    <property name="validator" ref="validator"/>
</bean>

弹簧服务的定义:

@Service("studentService")
@Validated
public class StudentService {

    @Autowired
    private StudentMapper studentMapper;

    @Transactional
    public void insertStudent(@Valid Student student) {
        studentMapper.insertStudent(student);
    }
}

pom.xml的内容

<dependency>
    <groupId>org.hibernate</groupId>
    <artifactId>hibernate-validator</artifactId>
    <version>5.2.1.Final</version>
</dependency>
<dependency>
    <groupId>javax.el</groupId>
    <artifactId>javax.el-api</artifactId>
    <version>2.2.4</version>
</dependency>

<dependency>
    <groupId>org.mybatis</groupId>
    <artifactId>mybatis</artifactId>
    <version>3.2.7</version>
</dependency>
<dependency>
    <groupId>org.mybatis</groupId>
    <artifactId>mybatis-spring</artifactId>
    <version>1.2.2</version>
</dependency>

当我使用 @NotNull 而不是 @Valid 在方法声明中,所有工作正常(当我传递null而不是Student类的实例时,Validation Framework抛出异常)。

我做错了什么?或者String中的方法级验证不支持参数的@Valid注释?