Java Spring Thymeleaf 将枚举集合绑定(bind)到复选框时出错

Question

我正在使用 Java8、Spring Boot 1.2.3 和 Thymeleaf 编写应用程序。我想在 Accommodation 类中使用 AccommodationType(枚举)集合，并将它们显示为复选框，以便用户能够选择住宿中可用的 AccommodationType。

不幸的是，当我尝试显示 createAccommodation 页面时出现错误:

2016-03-09 23:07:09.176 ERROR 29740 --- [nio-8080-exec-7] org.thymeleaf.TemplateEngine             : [THYMELEAF][http-nio-8080-exec-7] Exception processing template "createAccommodation": Error during execution of processor 'org.thymeleaf.spring4.processor.attr.SpringInputCheckboxFieldAttrProcessor' (createAccommodation:73)
2016-03-09 23:07:09.183 ERROR 29740 --- [nio-8080-exec-7] o.a.c.c.C.[.[.[/].[dispatcherServlet]    : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is org.thymeleaf.exceptions.TemplateProcessingException: Error during execution of processor 'org.thymeleaf.spring4.processor.attr.SpringInputCheckboxFieldAttrProcessor' (createAccommodation:73)] with root cause

java.lang.IllegalStateException: Neither BindingResult nor plain target object for bean name 'types' available as request attribute
    at org.springframework.web.servlet.support.BindStatus.<init>(BindStatus.java:144)
    at org.thymeleaf.spring4.util.FieldUtils.getBindStatusFromParsedExpression(FieldUtils.java:396)
    at org.thymeleaf.spring4.util.FieldUtils.getBindStatus(FieldUtils.java:323)
    at org.thymeleaf.spring4.util.FieldUtils.getBindStatus(FieldUtils.java:289)
.....

我的模型，简化:

public enum AccommodationType {
    singleRoom,
    doubleRoom,
    moreBeddedRoom,
    apartment;    
}

public class Accommodation {

    @Id
    private String id;

    @NotEmpty
    private String name;

    @NotNull
    private BigDecimal price;

    private List<AccommodationType> types = new ArrayList<AccommodationType>();

    .....

    public List<AccommodationType> getTypes() {
        return new ArrayList<AccommodationType>(types);
    }

    public void setTypes(List<AccommodationType> types) {
        types = new ArrayList<AccommodationType>(types);
    }
}

Controller :

@Controller
public class AccommodationController {

    private final AccommodationRepository accommodationRepository;

    @Autowired
    public AccommodationController(
            AccommodationRepository anAccommodationRepository) {
        this.accommodationRepository = anAccommodationRepository;
    }

    @ModelAttribute("allTypes")
    public List<AccommodationType> populateAccommodationTypes() {
        return Arrays.asList(AccommodationType.values());
    }

    @RequestMapping(value = "/accommodation/create", method = RequestMethod.GET)
    public ModelAndView showCreateAccommodationPage() {
        return new ModelAndView("createAccommodation", "accommodation",
                new Accommodation());
    }

    @RequestMapping(value = "/accommodation/create", method = RequestMethod.POST)
    public String handleAccommodationCreate(
            @Valid @ModelAttribute("accommodation") Accommodation anAccommodation,
            BindingResult aBindingResult) {
        if (aBindingResult.hasErrors()) {
            return "createAccommodation";
        }
        accommodationRepository.save(anAccommodation);
        return "redirect:/accommodation";
    }
}

View 模板:

<form class="form-horizontal" role="accommodation" th:action="@{/accommodation/create}" method="post">
....
<div class="form-group">
    <ul>
      <li th:each="type : ${allTypes}">
        <input type="checkbox" th:field="*{types}" th:value="${type}" />
        <label th:for="${#ids.prev('types')}" th:text="#{${type}}"></label>
      </li>
    </ul>
</div>
....

有人知道我做错了什么吗？

Answer 1

问题是表单标记中缺少 th:object:

<form class="form-horizontal" th:object="${accommodation}"
                        th:action="@{/accommodation/create}" method="post">