了解在Spring MVC中使用@ModelAttribute和@RequestAttribute注释 [英] Understanding the use of @ModelAttribute and @RequestAttribute annotations in Spring MVC

问题描述

我在Spring MVC中很新。目前，我正在研究演示Spring MVC功能的 Spring MVC Showcase web框架。

我有一些问题要了解在这个例子中如何处理Custom Resolable Web Arguments。

在实践中我有以下情况。在我的 home.jsp 视图中，我有以下链接：

 < a id =customArg class =textLinkhref =< c：url value =/ data / custom/>> Custom< / a> 
  

此链接为URL生成HTTP请求：/ data / custom strong>

包含处理此请求的方法的控制器类具有以下代码：

  @Controller 
 public class CustomArgumentController {
 
 @ModelAttribute 
 void beforeInvokingHandlerMethod（HttpServletRequest request）{
 request.setAttribute（foo 酒吧）; 
} 
 
 @RequestMapping（value =/ data / custom，method = RequestMethod.GET）
 public @ResponseBody字符串自定义（@RequestAttribute（foo）String foo ）{
 returnGot'f​​oo'request attribute value'+ foo +'; 
} 
 
} 
  

处理此HTTP请求的方法是 custom（）。所以当上一个链接被点击时，HTTP请求是通过自定义方法来处理的。

我有一些问题要明白什么是@RequestAttribute 注释做。我认为，在这种情况下，它将名为foo的请求属性绑定到一个新的String foo变量。但是这个属性是从哪里取的？这个变量是由Spring采用的吗？

好的，我的想法是这个请求属性取自HttpServletRequest对象。我认为是这样的，因为在这个类中，我还有一个具有说话名称的 beforeInvokingHandlerMethod（）方法，所以看起来这个方法设置一个属性，它们有 name = foo 和 value = bar ，在HttpServletRequest对象中，然后custom（）方法可以使用此值。

其实我的输出是：

获取'foo'请求属性值'bar'

为什么 beforeInvokingHandlerMethod（）在 custom（）方法之前调用？

为什么 beforeInvokingHandlerMethod（）由 @ModelAttribute 注释注释？在这种情况下是什么意思？

解决方案

RequestAttribute 但您在表单提交中传递的参数。让我们了解一个示例

假设我有以下表单

 < form action =...> 
< input type = hidden name = param1 id = param1 value = test /> 
< / form> 
  

现在，如果我有下面的控制器映射与请求url映射与表单提交如下。

  @Controller 
 public class CustomArgumentController {
 
 @ModelAttribute 
 void beforeInvokingHandlerMethod（HttpServletRequest request）{
 request.setAttribute（foo，bar）; 
} 
 
 
 @RequestMapping（value =/ data / custom，method = RequestMethod.GET）
 public @ResponseBody字符串custom（@RequestAttribute（param1 ）String param1）{
 //这里，我将在String对象中具有param1的值作为测试，它将映射我的Spring本身
} 
  

I am pretty new in Spring MVC. Currently I am studying the Spring MVC Showcase, that demonstrates the features of the Spring MVC web framework.

I have some problem to understand how Custom Resolvable Web Arguments are handled in this example.

In practice I have the following situation. In my home.jsp view I have the following link:

<a id="customArg" class="textLink" href="<c:url value="/data/custom" />">Custom</a> 

This link generate an HTTP Request towards the URL: "/data/custom"

The controller class that contain the method that handles this request have the following code:

@Controller
public class CustomArgumentController {

    @ModelAttribute
    void beforeInvokingHandlerMethod(HttpServletRequest request) {
        request.setAttribute("foo", "bar");
    }

    @RequestMapping(value="/data/custom", method=RequestMethod.GET)
    public @ResponseBody String custom(@RequestAttribute("foo") String foo) {
        return "Got 'foo' request attribute value '" + foo + "'";
    }

}

The method that handles this HTTP Request is custom(). So when the previous link is clicked, the HTTP Request is handled by the custom method.

I have some problem to understand what exactly does the @RequestAttribute annotation do. I think that, in this case, it binds the request attribute named foo to a new String foo variable. But where this attribute is taken from? Is this variable taken by Spring?

OK, my idea is that this request attribute is taken from a HttpServletRequest object. I think so because, in this class, I also have the beforeInvokingHandlerMethod() method that have a speaking name, so it seems that this method sets an attribute, that have name=foo and value=bar, inside an HttpServletRequest object, and then so the custom() method can use this value.

In fact my output is:

Got 'foo' request attribute value 'bar'

Why the beforeInvokingHandlerMethod() is called before the custom() method?

And why the beforeInvokingHandlerMethod() is annotated by @ModelAttribute annotation? What does it mean in this case?

解决方案

The RequestAttribute is nothing but the parameters which you have passed in the form submission. Lets understand with a sample example

Suppose I have the below form

<form action="...">
<input type=hidden name=param1 id=param1 value=test/>
</form>

Now, if I have the below controller which is mapped with the request url which is mapped with the form submission as below.

@Controller
public class CustomArgumentController {

@ModelAttribute
void beforeInvokingHandlerMethod(HttpServletRequest request) {
    request.setAttribute("foo", "bar");
}


@RequestMapping(value="/data/custom", method=RequestMethod.GET)
public @ResponseBody String custom(@RequestAttribute("param1") String param1 ) {
    // Here, I will have value of param1 as test in String object which will be mapped my Spring itself
}

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