在spring mvc表单中保留post中的对象

我正在使用SpringMVC。我有一个预构建的对象，作为ModelAttribute传递给视图。此对象用于显示窗体内的某些信息。然后，在填充表单后，通过表单中的path属性设置前一个对象的属性：select标记。当我检索这个对象时，我只看到用post更新的属性，并且该对象之前设置的所有属性现在都具有null值。我想知道我必须做什么才能不丢失对象的这些属性，这样我才能访问它们

这就是目标：

public class VocabularyRegisterDto {

    private  List<String> availableVocabularies;
    private String vocabularyToRegister; 
    
    ... constructors setters and getters ...

表单视图

<form:form action="vocabulary/register" method="post" modelAttribute="vocabularyRegister">
            <form:select path="vocabularyToRegister" id="register-vocabulary-dropdown">
                <c:forEach items="${vocabularyRegister.availableVocabularies}" var="vocabulary">
                        <form:option value="${vocabulary}"/>
                </c:forEach>
            </form:select>
            <input id="register-vocabulary-button" type="submit" value="Submit"/>
</form:form>

在post控制器之后执行的方法

@RequestMapping(value = "/vocabulary/register", method = RequestMethod.POST)
    public String registerVocabulary(@ModelAttribute VocabularyRegisterDto vocabularyRegisterDto,
                                     HttpServletRequest request) {
        String vocabularyRegister = vocabularyRegisterDto.getVocabularyToRegister(); // Here I do get the option selected in the form
        List<String> vocabularyRegister = vocabularyRegisterDto.availableVocabularies(); // But here I get null even though this list was already used in the view to display all the options

        return "redirect:/profile";
    }

@RequestMapping（value=“/词汇表/register”，method=RequestMethod.POST）
公共字符串注册表可撤销性（@ModelAttribute VocabularyRegisterTo VocabularyRegisterTo，
HttpServletRequest（请求）{
String-vocabularyRegister=vocabularyRegisterDto.getVocabularyToRegister（）；//这里我得到了表单中选择的选项
List-vocabularyRegister=vocabularyRegisterDto.availableVocabularies（）；//但是这里我得到了null，即使该列表已经在视图中用于显示所有选项
返回“重定向：/profile”；
}

@RequestMapping(value = "/vocabulary/register", method = RequestMethod.POST)
    public String registerVocabulary(@ModelAttribute VocabularyRegisterDto vocabularyRegisterDto,
                                     HttpServletRequest request) {
        String vocabularyRegister = vocabularyRegisterDto.getVocabularyToRegister(); // Here I do get the option selected in the form
        List<String> vocabularyRegister = vocabularyRegisterDto.availableVocabularies(); // But here I get null even though this list was already used in the view to display all the options

        return "redirect:/profile";
    }