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我通读了类似的问题，不幸的是没有找到解决方案。
我正在向@ModelAttribute我的 JSP 发送一个 Student 实体，允许用户对其进行编辑。当 Student 被 POST 回控制器 ( StudentController) 时，字段rates和id为空。空值rates是可以的，我将学生的费率作为单独的@RequestParam. 其他字段正常。但是id意外地为空。
我正在使用 Java 8、Spring 4.1、Tomcat 7.0.55、JSTL 1.2。

这是我的相关部分StudentController：

@Controller
@RequestMapping(value = "/student")
public class StudentController {

    @Autowired
    private StudentService studentService;
    @Autowired
    private FacultyService facultyService;

    @RequestMapping(value = "/edit/{id:.+}", method = RequestMethod.GET)
    public ModelAndView editStudentPage(@PathVariable Long id) {
        ModelAndView mav = new ModelAndView("student-edit");

        Student student = (id > 0)? studentService.findById(id) : new Student();
        mav.addObject("student", student);
        // or
        //mav.getModelMap().addAttribute(student);

        /* other objects omitted */

        return mav;
    }

    @RequestMapping(value = "/edit/{id:.+}", method = RequestMethod.POST)
    public ModelAndView editStudent(
            @ModelAttribute Student student,
            @RequestParam(value="rates", required = false) String ratesString,
            @PathVariable Long id,
            final RedirectAttributes redirectAttributes) throws StudentNotFoundException {
        ModelAndView mav = new ModelAndView("redirect:/student/list");

        student = studentService.update(student);
        student.updateRates(ratesString);

        String msg = "Student was successfully updated";
        redirectAttributes.addFlashAttribute("message", msg);
        return mav;
    }

    /* ... */
}

这是一个学生编辑的 JSP 文件：

<jsp:useBean id="student" scope="request" class="by.naxa.demo.model.Student" />
<!-- I've tried to comment out the above line in order to avoid collision with `modelAttribute` (in hope that this was a culprit) -->
<%@page contentType="text/html;charset=UTF-8" language="java" %>
<%@taglib prefix="c"    uri="http://java.sun.com/jsp/jstl/core" %>
<%@taglib prefix="form" uri="http://www.springframework.org/tags/form" %>

<c:url var="formAction" value="/student/edit/${student.id}" /> <!-- simplified -->

<!-- <head> omitted -->
<body>
<form:form action="${formAction}" method="POST" modelAttribute="student" >
    <form:hidden path="id" /> <!-- I've tried to specify `value="${student.id}"` here -->

    <div>
        <form:label path="name">Student's name:</form:label>
        <form:input path="name" required="true"/><br />
        <!-- other fields omitted -->

        <input type="submit" value="Save" />
        <!-- `Cancel` omitted -->
    </div>
</form:form>
</body>

我看到生成页面上的输入填充了正确的值：

<input id="id" name="id" value="1" type="hidden" />
<input id="name" name="name" required="true" type="text" value="John Snow"/>

网页.xml：

<!-- Creates the Spring Container shared by all Servlets and Filters -->
<listener>
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>

<!-- Processes application requests -->
<servlet>
    <servlet-name>appServlet</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <init-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>/WEB-INF/spring/app/servlet-context.xml</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
</servlet>

<servlet>
    <servlet-name>jsp</servlet-name>
    <servlet-class>org.apache.jasper.servlet.JspServlet</servlet-class>
    <load-on-startup>2</load-on-startup>
</servlet>

<servlet-mapping>
    <servlet-name>appServlet</servlet-name>
    <url-pattern>/*</url-pattern>
</servlet-mapping>

<servlet-mapping>
    <servlet-name>jsp</servlet-name>
    <url-pattern>/WEB-INF/views/*</url-pattern>
</servlet-mapping>

<welcome-file-list>
    <welcome-file />
</welcome-file-list>

Spring servlet-context.xml 中的 ViewResolver：

<!-- Resolves views selected for rendering by @Controllers to .jsp resources in the /WEB-INF/views directory -->
<bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
    <property name="viewClass" value="org.springframework.web.servlet.view.JstlView" />
    <property name="prefix" value="/WEB-INF/views/" />
    <property name="suffix" value=".jsp" />
</bean>

学生类扩展了 AbstractNamedPersistable。它们在这里（用 Lombok 和 JPA 注释）：

@Entity
@NoArgsConstructor
@EqualsAndHashCode(callSuper = true)
@ToString(callSuper = true, includeFieldNames = false)
@NamedQuery(name = "Student.findByTheStudentsName", query = "select s from Student s where s.name = ?1")
public @Data class Student extends AbstractNamedPersistable<Long> {
    /* all fields and `updateRates(String)` omitted */
}

@MappedSuperclass
@EqualsAndHashCode(callSuper = false)
@NoArgsConstructor
@AllArgsConstructor
public abstract @Data class AbstractNamedPersistable<PK extends Serializable> extends AbstractPersistable<PK> {

    @Column(name = "Name", nullable = false, unique = true)
    private String name;

    @Override
    public String toString() {
        return getName();
    }
}

可能是什么问题呢？

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