@ModelAttribute 和 org.springframework.ui.ModelMap.get() 之间的区别？
我正在尝试使用对象作为 <%@ taglib uri="http://www.springframework.org/tags/form" prefix="form"%> 的命令对象>元素。
在控制器的 GET 方法中，我添加如下对象：
@RequestMapping(method = RequestMethod.GET)
public String renderForm(ModelMap model, HttpServletRequest request) {
[...]
model.addAttribute("voting", voting);
[...]
}
渲染的表单在定义如下时正确显示命令对象：
<form:form action="vote" method="PUT" commandName="voting" name="oform">
现在，当尝试在控制器中重新访问表单的命令对象时，在 POST 方法上，我有两种方法。首先，我在签名中声明 @ModelAttribute：
@RequestMapping(method = RequestMethod.PUT)
public String newVoting(@ModelAttribute("voting") Voting voting, HttpServletRequest request) { [...]}
或者我访问 ModelMap 并从底层映射中获取值：
@RequestMapping(method = RequestMethod.PUT)
public String newVoting(ModelMap model, HttpServletRequest request) {
Voting voting = (Voting) model.get("voting");
[...]
}
执行第一个操作时，我获取表单提交的对象。执行后者时，我得到了对象在被表单处理之前的样子。
为什么表单的提交不会更改 ModelMap 中的对象以及为什么 @ModelAttribute 与实际模型中的不同？我觉得名称“ModelAttribute”应该产生与直接从模型获取对象相同的对象。
也许 @ModelAttribute 有点误导？
编辑 忘记提及该对象是 @SessionAttributes
@SessionAttributes({"voting", "state"})
I'm trying to use an Object as the command object of a <%@ taglib uri="http://www.springframework.org/tags/form" prefix="form"%>element.
In the controller's GET method, I add the Object like this:
@RequestMapping(method = RequestMethod.GET)
public String renderForm(ModelMap model, HttpServletRequest request) {
[...]
model.addAttribute("voting", voting);
[...]
}
The rendered form does show the command object correctly when defined like this:
<form:form action="vote" method="PUT" commandName="voting" name="oform">
Now when trying to access the form's command object back in the controller, on the POST method, I have two approaches. First, I declare the @ModelAttribute in the signature:
@RequestMapping(method = RequestMethod.PUT)
public String newVoting(@ModelAttribute("voting") Voting voting, HttpServletRequest request) { [...]}
Or I access the ModelMap and get the value from the underlying map:
@RequestMapping(method = RequestMethod.PUT)
public String newVoting(ModelMap model, HttpServletRequest request) {
Voting voting = (Voting) model.get("voting");
[...]
}
When doing the first, I get the object as it was submitted by the form. Doing the latter, I get the object as it was BEFORE being handled by the form.
Why does the form's submit not change the object in the ModelMap and why does the @ModelAttribute differ from whats in the actual model? I feel like the name 'ModelAttribute' should result in the same object like getting the object directly from the model.
Maybe @ModelAttribute is kind of misleading?
EDIT
Forgot to mention that the object is a @SessionAttributes
@SessionAttributes({"voting", "state"})
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您的第一种方法，使用 @ModelAttribute 注释做两件事：
您的第二种方法仅使用 ModelMap，因此它仅获取模型属性（从请求或在您的情况下从会话获取，具体取决于 @SessionAttributes 注释）。此方法不使用提交表单中的数据。
Your first approach, using the @ModelAttribute annotation does two things:
Your second approach uses just the ModelMap, so it's getting only model attributes (from the request or, in your case, the session, depending on the @SessionAttributes annotation). This approach does not use the data from the submitted form.