java - BindingResult 和 bean 名称 'student' 的普通目标对象都不能作为请求属性 - Spring MVC

Question

首先，我想说，我已经在 SO(和其他地方)上阅读了许多有关此错误的问题和答案，但对这个特定案例没有帮助。

我的简单 Spring MVC Web 应用程序的场景是这样的:用户根据 String 属性 indexNumber 搜索学生 (searchStudent.jsp)。 indexNumber 由用户输入的其他 3 个属性组成:programId、rollNumber、rollYear。例如，如果programId =“M5”，rollNumber =“10”和rollYear =“2013”​​，则indexNumber将为“M5 10/13”。这是在 View 中完成的。 indexNumber是每个学生的唯一标识符，但不是PK。重要提示:搜索学生并加载适当的页面本身就可以正常工作。

如果学生不存在，addAfterSearchStudent.jsp 页面应该加载用户在 searchStudent.jsp 中输入的预填充值(programId、rollNumber、indexNumber) - 我不想让用户输入此数据两次。我编写了下面的代码，我认为它会完全按照我在此处描述的方式进行操作，但我收到了上述错误。当我对这些属性进行硬编码并尝试保存数据时，这也可以正常工作。我相信问题在于将参​​数从一个jsp传递到另一个jsp。

这些是我的 Controller 的处理程序方法:

    /**
     * Handles and retrieves the search student page
     */
    @RequestMapping(value="/search", method = RequestMethod.GET)
    public String getSearchStudent(Model model) {

        logger.debug("Received request to show search student page");

        model.addAttribute("index", new Student());
        model.addAttribute("programList", programService.getAll());

        return "searchStudent";
    }

    /**
     * Searches for a student by delegating the processing to StudentService.
     */
    @RequestMapping(value="/search", method = RequestMethod.POST)
    public String postSearchStudent(@RequestParam(value = "program.programId") String programId,
                                    @RequestParam(value = "rollNumber") String rollNumber,
                                    @RequestParam(value = "rollYear") String rollYear,
                                    @RequestParam(value = "indexNumber") String indexNumber,
                                    Model model) {

        logger.debug("Received request to search for a student");

        model.addAttribute("program.programId", programId);
        model.addAttribute("rollNumber", rollNumber);
        model.addAttribute("rollYear", rollYear);
        model.addAttribute("indexNumber", indexNumber);

        // Call StudentService to do the actual searching
        Student student = studentService.search(indexNumber);

        // if student isn't in the db load addAfterSearchStudent.jsp, else load student.jsp
        if (student == null)
            return "addAfterSearchStudent";
        else
            return "student";
    }

    /**
     * Handles and retrieves the add (after search) student page
     */
    @RequestMapping(value="/addSearch", method = RequestMethod.GET)
    public String getAddSearchStudent(@RequestParam(value = "program.programId") String programId,
                                    @RequestParam(value = "rollNumber") String rollNumber,
                                    @RequestParam(value = "rollYear") String rollYear,
                                    @RequestParam(value = "indexNumber") String indexNumber,
                                    Model model) {

        logger.debug("Received request to show add (after search) student page");

        Student student = new Student();
        student.setRollNumber(rollNumber);
        student.setRollYear(rollYear);
        student.setIndexNumber(indexNumber);
        Program program = programService.get(programId);
        student.setProgram(program);
        model.addAttribute("student", student);

        return "addAfterSearchStudent";
    }

    /**
     * Adds a new student after search by delegating the processing to StudentService.
     * Displays a confirmation JSP page
     */
    @RequestMapping(value="/addSearch", method = RequestMethod.POST)
    public String postAddSearchStudent(@ModelAttribute("student") Student student) {

        logger.debug("Received request to add new student after search");

        // Call StudentService to do the actual adding
        studentService.addAfterSearch(student);

        // resolves to /WEB-INF/jsp/success/addStudentSuccess.jsp
        return "/success/addStudentSuccess";
    }

这是 searchStudent.jsp:

<c:url var="searchUrl" value="/essays/main/student/search" />
<form:form modelAttribute="index" method="POST" action="${searchUrl}">
...

这是 addAfterSearchStudent.jsp:

<c:url var="saveUrl" value="/essays/main/student/addSearch" />
<form:form commandName="student" method="POST" action="${saveUrl}">
...

我知道这很长，但我想呈现所有相关信息。有人知道我在哪里犯了错误吗？

Answer 1

<form:form commandName="student" ...>

您的 addAfterSearchStudent.jsp 需要一个名为“student”的对象。在您的 postSearchStudent() 方法中，您不会向模型中添加一个。

if (student == null)
  return "addAfterSearchStudent";

您需要创建一个 Student 对象并添加它，就像在 getAddSearchStudent() 方法中执行的操作一样。

    Student student = new Student();
    student.setRollNumber(rollNumber);
    student.setRollYear(rollYear);
    student.setIndexNumber(indexNumber);
    Program program = programService.get(programId);
    student.setProgram(program);
    model.addAttribute("student", student);