提交表单时Spring绑定异常

卡住了，不知道为什么 Spring Form 在 get 中预填充时无法成功提交[给出绑定问题]Request call loadForm，但在方法中填充时工作正常setupFormObject with @ModelAttribute注释标签。我可以在 github 中提供一个简单的示例来测试是否需要:)

下面的例子

@ModelAttribute("showForm")
public ShowForm setupFormObject() {
    //Instantiate showForm with data
    return showForm;
}

@RequestMapping(method = RequestMethod.GET)
public ModelAndView loadForm(@RequestParam("id") String id, HttpSession session) {    
    ModelAndView modelAndView = new ModelAndView(nextPage);
    //Instantiate showForm with data
    //modelAndView.addObject("showForm", showForm);
    return modelAndView;
}

@RequestMapping(method = RequestMethod.POST)
public String post(@ModelAttribute("showForm") ShowForm showForm, BindingResult result, final RedirectAttributes redirectAttrs) {
     //I see changed data here in showForm when populated using @setupFormObject
     //See an exception in JSP with binding error if populated in loadForm
     return "";
 }

根据要求进行堆栈跟踪。这个异常来自github https://github.com/hth/StatusInvoke例子。

`HTTP Status 500 - Request processing failed; nested exception is org.springframework.beans.InvalidPropertyException: Invalid property 'users[0]' of bean class [com.example.UserForm]: Illegal attempt to get property 'users' threw exception; nested exception is org.springframework.beans.NullValueInNestedPathException: Invalid property 'users' of bean class [com.example.UserForm]: Could not instantiate property type [com.example.UserEntity] to auto-grow nested property path: java.lang.InstantiationException: com.example.UserEntity`

`type Exception report`

`message Request processing failed; nested exception is org.springframework.beans.InvalidPropertyException: Invalid property 'users[0]' of bean class [com.example.UserForm]: Illegal attempt to get property 'users' threw exception; nested exception is org.springframework.beans.NullValueInNestedPathException: Invalid property 'users' of bean class [com.example.UserForm]: Could not instantiate property type [com.example.UserEntity] to auto-grow nested property path: java.lang.InstantiationException: com.example.UserEntity`

`description The server encountered an internal error that prevented it from fulfilling this request.`

`exception`

`org.springframework.web.util.NestedServletException: Request processing failed; nested exception is org.springframework.beans.InvalidPropertyException: Invalid property 'users[0]' of bean class [com.example.UserForm]: Illegal attempt to get property 'users' threw exception; nested exception is org.springframework.beans.NullValueInNestedPathException: Invalid property 'users' of bean class [com.example.UserForm]: Could not instantiate property type [com.example.UserEntity] to auto-grow nested property path: java.lang.InstantiationException: com.example.UserEntity`
    `org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:927)
    org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:822)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
    org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:796)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:728)`

`root cause`

`org.springframework.beans.InvalidPropertyException: Invalid property 'users[0]' of bean class [com.example.UserForm]: Illegal attempt to get property 'users' threw exception; nested exception is org.springframework.beans.NullValueInNestedPathException: Invalid property 'users' of bean class [com.example.UserForm]: Could not instantiate property type [com.example.UserEntity] to auto-grow nested property path: java.lang.InstantiationException: com.example.UserEntity
    org.springframework.beans.BeanWrapperImpl.getPropertyValue(BeanWrapperImpl.java:829)
    org.springframework.beans.BeanWrapperImpl.getNestedBeanWrapper(BeanWrapperImpl.java:556)
    org.springframework.beans.BeanWrapperImpl.getBeanWrapperForPropertyPath(BeanWrapperImpl.java:533)
    org.springframework.beans.BeanWrapperImpl.setPropertyValue(BeanWrapperImpl.java:894)
    org.springframework.beans.AbstractPropertyAccessor.setPropertyValues(AbstractPropertyAccessor.java:75)
    org.springframework.validation.DataBinder.applyPropertyValues(DataBinder.java:699)
    org.springframework.validation.DataBinder.doBind(DataBinder.java:595)
    org.springframework.web.bind.WebDataBinder.doBind(WebDataBinder.java:191)
    org.springframework.web.bind.ServletRequestDataBinder.bind(ServletRequestDataBinder.java:112)
    org.springframework.web.servlet.mvc.method.annotation.ServletModelAttributeMethodProcessor.bindRequestParameters(ServletModelAttributeMethodProcessor.java:153)
    org.springframework.web.method.annotation.ModelAttributeMethodProcessor.resolveArgument(ModelAttributeMethodProcessor.java:106)
    org.springframework.web.method.support.HandlerMethodArgumentResolverComposite.resolveArgument(HandlerMethodArgumentResolverComposite.java:77)
    org.springframework.web.method.support.InvocableHandlerMethod.getMethodArgumentValues(InvocableHandlerMethod.java:162)
    org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:123)
    org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:104)
    org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandleMethod(RequestMappingHandlerAdapter.java:746)
    org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:687)
    org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:80)
    org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:925)
    org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:856)
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:915)
    org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:822)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
    org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:796)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
`

非常感谢您的帮助

Thanks

问题实际上是 UserEntity 没有默认构造函数，如果添加构造函数，它将正常工作：

public UserEntity(){
    //
}