Spring mvc 如何将集合元素分配给Thymeleaf中的form字段

我可以看到列表在Thymeleaf表单中的成功使用

更新2

把一些代码

第一次调用create时，表单显示为空行

当我单击“保存”或“添加新行”时，在调用controller save（）之前会出现该错误

若我注释掉th：字段行，那个么错误就消失了

控制器

@GetMapping({"/create"})
public String create(ModelMap model){
    CatDescr catDescr = new CatDescr();         
    //add 1 empty row for catDescrDt
    int noOfCatDescrDts = 1;
    catDescr.setCatDescrDts(getNewCatDescrDts(noOfCatDescrDts, catDescr));  
    model.addAttribute("catDescr", catDescr);   
    return "catDescr/create";
}

@PostMapping(value="/create", params={"save"})
public String save(final CatDescr catDescr
        , final BindingResult bindingResult, final ModelMap model){     
    ...
    CatDescr updatedCatDescr = catDescrService.save(catDescr);  
    model.clear();
    return "redirect:/catDescr/create";

}

@RequestMapping(value="/create", params={"addCatDescrDtRow"})
public String addCatDescrDtRow(ModelMap model, final CatDescr catDescr, final BindingResult bindingResult) {
    catDescr.getCatDescrDts().add(new CatDescrDt());
    ...
    return "catDescr/create";
}

看法

---

必须在实体中使用自定义getter/setter返回Set as List，而是在Thymeleaf中绑定该列表，以便通过索引访问它

在中，控制器必须将列表成员与集合成员同步

---

所有这些都归功于@Dark，精彩的解释以及有用的链接。

是的，它应该可以很好地与Set一起工作，事实上，任何Iterable或数组都应该很好。虽然您可能无法保证集合元素的顺序。如果尝试，则无效。错误似乎出现在像数组一样访问集合的行上。已发布堆栈跟踪。。谢谢。异常似乎表明您正试图从集合中访问第一个元素，但集合是空的。@Janar是的，您是对的。除了代码中的任何地方，我都尝试直接访问集合的元素，例如[0]。检查我的控制器，设置不为空。视图最初显示表单，当我发布（保存或添加新行）时，我收到此错误。堆栈跟踪似乎指示发布时出错，而不是到达控制器。将把代码片段放在更新2中。对不起，我想我误解了你的问题。也许我应该澄清一下，您可以在Thymeleaf中使用Set fine的计数器和索引，但不能将控制器中的Set直接绑定到对象。Spring使用getter和setter来绑定它不能通过使用集合的索引来绑定的对象。尝试自定义getter/setter，如

Caused by: org.springframework.beans.InvalidPropertyException: Invalid property 'catDescrDts[0]' of bean class [ae.tbits.atn.aiwacore.common.model.CatDescr]: Cannot get element with index 0 from Set of size 0, accessed using property path 'catDescrDts[0]'
at org.springframework.beans.AbstractNestablePropertyAccessor.getPropertyValue(AbstractNestablePropertyAccessor.java:661)
... 51 more
2017-07-13 16:23:57 ERROR ErrorController:19 - Exception during execution of SpringSecurity application
org.springframework.beans.InvalidPropertyException: Invalid property 'catDescrDts[0]' of bean class [ae.tbits.atn.aiwacore.common.model.CatDescr]: Illegal attempt to get property 'catDescrDts' threw exception; nested exception is org.springframework.beans.InvalidPropertyException: Invalid property 'catDescrDts[0]' of bean class [ae.tbits.atn.aiwacore.common.model.CatDescr]: Cannot get element with index 0 from Set of size 0, accessed using property path 'catDescrDts[0]'
at org.springframework.beans.AbstractNestablePropertyAccessor.getPropertyValue(AbstractNestablePropertyAccessor.java:708)
at org.springframework.beans.AbstractNestablePropertyAccessor.getNestedPropertyAccessor(AbstractNestablePropertyAccessor.java:836)
at org.springframework.beans.AbstractNestablePropertyAccessor.getPropertyAccessorForPropertyPath(AbstractNestablePropertyAccessor.java:813)
at org.springframework.beans.AbstractNestablePropertyAccessor.setPropertyValue(AbstractNestablePropertyAccessor.java:270)
at org.springframework.beans.AbstractPropertyAccessor.setPropertyValues(AbstractPropertyAccessor.java:95)
at org.springframework.validation.DataBinder.applyPropertyValues(DataBinder.java:834)
at org.springframework.validation.DataBinder.doBind(DataBinder.java:730)
at org.springframework.web.bind.WebDataBinder.doBind(WebDataBinder.java:192)
at org.springframework.web.bind.ServletRequestDataBinder.bind(ServletRequestDataBinder.java:106)
at org.springframework.web.servlet.mvc.method.annotation.ServletModelAttributeMethodProcessor.bindRequestParameters(ServletModelAttributeMethodProcessor.java:150)
at org.springframework.web.method.annotation.ModelAttributeMethodProcessor.resolveArgument(ModelAttributeMethodProcessor.java:114)
at org.springframework.web.method.support.HandlerMethodArgumentResolverComposite.resolveArgument(HandlerMethodArgumentResolverComposite.java:121)
at org.springframework.web.method.support.InvocableHandlerMethod.getMethodArgumentValues(InvocableHandlerMethod.java:161)
at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:128)
at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:114)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:827)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:738)
at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:963)
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:897)
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:872)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:707)
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
at io.undertow.servlet.handlers.ServletHandler.handleRequest(ServletHandler.java:85)
at io.undertow.servlet.handlers.security.ServletSecurityRoleHandler.handleRequest(ServletSecurityRoleHandler.java:62)
at io.undertow.servlet.handlers.ServletDispatchingHandler.handleRequest(ServletDispatchingHandler.java:36)
at org.wildfly.extension.undertow.security.SecurityContextAssociationHandler.handleRequest(SecurityContextAssociationHandler.java:78)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at io.undertow.servlet.handlers.security.SSLInformationAssociationHandler.handleRequest(SSLInformationAssociationHandler.java:131)
at io.undertow.servlet.handlers.security.ServletAuthenticationCallHandler.handleRequest(ServletAuthenticationCallHandler.java:57)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at io.undertow.security.handlers.AbstractConfidentialityHandler.handleRequest(AbstractConfidentialityHandler.java:46)
at io.undertow.servlet.handlers.security.ServletConfidentialityConstraintHandler.handleRequest(ServletConfidentialityConstraintHandler.java:64)
at io.undertow.security.handlers.AuthenticationMechanismsHandler.handleRequest(AuthenticationMechanismsHandler.java:60)
at io.undertow.servlet.handlers.security.CachedAuthenticatedSessionHandler.handleRequest(CachedAuthenticatedSessionHandler.java:77)
at io.undertow.security.handlers.NotificationReceiverHandler.handleRequest(NotificationReceiverHandler.java:50)
at io.undertow.security.handlers.AbstractSecurityContextAssociationHandler.handleRequest(AbstractSecurityContextAssociationHandler.java:43)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at org.wildfly.extension.undertow.security.jacc.JACCContextIdHandler.handleRequest(JACCContextIdHandler.java:61)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at io.undertow.servlet.handlers.ServletInitialHandler.handleFirstRequest(ServletInitialHandler.java:284)
at io.undertow.servlet.handlers.ServletInitialHandler.dispatchRequest(ServletInitialHandler.java:263)
at io.undertow.servlet.handlers.ServletInitialHandler.access$000(ServletInitialHandler.java:81)
at io.undertow.servlet.handlers.ServletInitialHandler$1.handleRequest(ServletInitialHandler.java:174)
at io.undertow.server.Connectors.executeRootHandler(Connectors.java:202)
at io.undertow.server.HttpServerExchange$1.run(HttpServerExchange.java:793)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)

Caused by: org.springframework.beans.InvalidPropertyException: Invalid property 'catDescrDts[0]' of bean class [ae.tbits.atn.aiwacore.common.model.CatDescr]: Cannot get element with index 0 from Set of size 0, accessed using property path 'catDescrDts[0]'
at org.springframework.beans.AbstractNestablePropertyAccessor.getPropertyValue(AbstractNestablePropertyAccessor.java:661)
... 51 more

@GetMapping({"/create"})
public String create(ModelMap model){
    CatDescr catDescr = new CatDescr();         
    //add 1 empty row for catDescrDt
    int noOfCatDescrDts = 1;
    catDescr.setCatDescrDts(getNewCatDescrDts(noOfCatDescrDts, catDescr));  
    model.addAttribute("catDescr", catDescr);   
    return "catDescr/create";
}

@PostMapping(value="/create", params={"save"})
public String save(final CatDescr catDescr
        , final BindingResult bindingResult, final ModelMap model){     
    ...
    CatDescr updatedCatDescr = catDescrService.save(catDescr);  
    model.clear();
    return "redirect:/catDescr/create";

}

@RequestMapping(value="/create", params={"addCatDescrDtRow"})
public String addCatDescrDtRow(ModelMap model, final CatDescr catDescr, final BindingResult bindingResult) {
    catDescr.getCatDescrDts().add(new CatDescrDt());
    ...
    return "catDescr/create";
}

<ul th:each="item, stat: *{catDescrDts}">
<li>
    <input type="text" th:field="*{catDescrDts[__${stat.index}__].name}" th:id="${'catDescrDts'+stat.index+'.name'}">
</li>