Spring:具有和不具有@ModelAttribute的绑定对象 [英] Spring : binding object with and without @ModelAttribute

问题描述

我是Spring的新用户并正在注册用户.我确实是这样.

I am new in Spring and registering a user.I did like this.

@RequestMapping("/register")
    public String register(@ModelAttribute User user,BindingResult result){
       if(!result.hasErrors()){
         userSerive.register(user);
       }
     return "welcome";
}

这很好，但是这里的问题是我在welcome.jsp页面中不需要此user对象，所以为什么要使模型对象变重.所以我尝试了不使用@ModelAttribute的情况，这对我也适用，如下所示

This worked fine,but problem here is I don't need this user object in my welcome.jsp page,so why make model object heavier.So I tried without @ModelAttribute, this also works for me like below.

@RequestMapping("/register")
    public String register(User user,BindingResult result){
       if(!result.hasErrors()){
         userSerive.register(user);
       }
     return "welcome";
}

所以我只想知道什么是优点和优点?和两者都有缺点，如果我真的不需要jsp中的user对象，这是最佳实践.是@ModelAttribute除了将对象添加到模型之外还做其他事情，它隐含了弹簧绑定不是.@ModelAttribute是更安全的绑定方式吗?

So I just want to know what are pros & cons of both and which is the best practice if I really don't need user object in jsp. Is @ModelAttribute does any other thing apart from adding object to Model,which spring implicit binding not does.Is @ModelAttribute safer way of binding or else?

我想将查询分为以下4种类型.@ModelAttribute和没有@ModelAttribute的区别是，如果我不需要在视图中发送数据并且我的请求是任何

I want to categories my query in following 4 type of request.what would be difference with and without @ModelAttribute if I need not to send data in view and my request is any of-

1. 查询字符串，即GET中的表单数据
2. 请求有效载荷或主体，即POST中的表单数据
ajaxized GET requst中的
3. json数据
POST请求中的
4. json数据-我猜这两个都不会绑定. @RequestBody是必需的.

1. query string ie form data in GET
2. request payload or body ie form data in POST
3. json data in ajaxified GET requst
4. json data in POST requst- I guess this would not be bind in any of both. @RequestBody is required.

推荐答案

在这种情况下，两种方法签名之间的行为可能没有差异(见下文...).

There is probably (see below...) no difference in the behaviour between the two method signatures in your case.

两者都将请求参数绑定到user，并将结果对象作为属性user添加到模型中-该属性名称是从方法参数User的大写字母类型名称派生的.

Both will bind the request parameters to user and add the resulting object to the model as the attribute user - this attribute name being derived from the decapitalised type name of the method argument, User.

@ModelAttribute可用于自定义属性名称，例如@ModelAttribute("theUser")，或者向您的代码读者提示在视图中使用此参数.但是正如您所说，这些都不适用于您的用例.

@ModelAttribute can be used to customise the name of the attribute, e.g. @ModelAttribute("theUser"), or to give a hint to the reader of your code that this argument is used in the view. But as you say, neither of these apply in your use case.

无论您是否使用@ModelAttribute批注，Spring中都将使用完全相同的代码填充参数-问题代码为org.springframework.web.servlet.mvc.method.annotation.ServletModelAttributeMethodProcessor.

Exactly the same code in Spring will be used to populate the argument whether you use the @ModelAttribute annotation or not - the code in question is org.springframework.web.servlet.mvc.method.annotation.ServletModelAttributeMethodProcessor.

因此，对于我来说，在代码中使用public String register(User user, BindingResult result)签名对我来说更有意义.在模型中不需要的方法参数上添加@ModelAttribute批注可能会使阅读代码的人感到困惑.

It therefore makes more sense to me for you to use the public String register(User user, BindingResult result) signature in your code. Adding a @ModelAttribute annotation to method arguments that are not required in the model could be confusing to people reading your code.

稍长一点的答案是，在您的情况下指定@ModelAttribute可能是大约的原因-但这相当不可思议，而且不太可能.

The slightly longer answer is that there could just about be a reason for specifying @ModelAttribute in your case - but it's quite arcane and unlikely.

方法参数由HandlerMethodArgumentResolver实例填充.这些是可配置的，并针对每个参数依次尝试.

Method arguments in Spring handler methods are populated by HandlerMethodArgumentResolver instances. These are configurable and are attempted in turn for each parameter.

默认的处理程序方法参数解析器如下所示(请参见RequestMappingHandlerAdapter):

The default handler method argument resolvers look like this (see RequestMappingHandlerAdapter):

resolvers.add(new ServletModelAttributeMethodProcessor(false));

...

resolvers.add(new ServletModelAttributeMethodProcessor(true));

如果要在中间添加自己的内容，例如UserHandlerMethodArgumentResolver，则可以使用@ModelAttribute告诉Spring以默认方式处理特定参数，而不是使用自定义参数解析程序类.

If you were to add your own in the middle, e.g. a UserHandlerMethodArgumentResolver, you could then use @ModelAttribute to tell Spring to process a specific argument in the default way, rather than use your custom argument resolver class.

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