在此Spring MVC展示示例中，如何使用@RequestAttribute和@ModelAttribute批注? [英] How is used @RequestAttribute and @ModelAttribute annotation in this Spring MVC showcase example?
问题描述
我在Spring MVC中还很陌生.
I am pretty new in Spring MVC.
在此期间，我正在研究可从STS下载的 Spring MVC展示示例仪表板.
In this period I am studying the Spring MVC showcase example downlodable from STS dashboard.
在理解此示例中如何处理自定义可解析Web参数时，我遇到了一些问题.
I am having some problems understanding how Custom Resolvable Web Arguments are handled in this example.
实际上，我有以下情况:
In practice I have the following situation:
在home.jsp视图中，我具有以下链接:
In my home.jsp view I have the following link:
<a id="customArg" class="textLink" href="<c:url value="/data/custom" />">Custom</a>
此链接针对URL生成HTTP请求:"/数据/自定义"
This link generate an HTTP Request towards the URL: "/data/custom"
包含处理该请求的方法的控制器类具有以下代码:
The controller class that contains the method that handles this request has 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 + "'";
}
}
处理此HTTP请求的方法为 custom()
The method that handles this HTTP Request is custom()
因此，当单击上一个链接时，HTTP请求由自定义方法处理...
So when the previous link is clicked the HTTP Request is handled by the custom method...
我在理解@RequestAttribute注释的内容方面遇到问题.
I am having problems understanding what the @RequestAttribute annotation.
我认为在这种情况下，它将名为foo的请求属性绑定到新的String foo变量.
I think that, in this case, it binds the request attribute named foo to a new String foo variable.
但是...此属性从何处获取?这个变量是Spring采取的吗?
But... where is this attribute taken from? Is this variable taken by Spring?
好吧...我的想法是该请求属性取自HttpServletRequest对象...
Ok...my idea is that this request attribute is taken from a HttpServletRequest object...
我认为这是因为，在该类中，我还具有beforeInvokingHandlerMethod()方法，该方法具有特定的名称...因此，看来该方法设置了一个属性，该属性内部具有name=foo和value=bar HttpServletRequest对象...然后custom()方法可以使用此值...
I think this because, in this class, I have also have the beforeInvokingHandlerMethod() method that have a speacking name...so it seems that this method seta an attribute, that have name=foo and value=bar, inside an HttpServletRequest object...and then so the custom() method can use this value...
实际上我的输出是:
Got 'foo' request attribute value 'bar'
为什么在custom()方法之前调用beforeInvokingHandlerMethod()?
Why is the beforeInvokingHandlerMethod() called before the custom() method?
为什么beforeInvokingHandlerMethod()用@ModelAttribute注释进行注释?这种情况是什么意思?
And why is the beforeInvokingHandlerMethod() annoted by @ModelAttribute annotation? What does this case mean?
推荐答案
您假设@RequestAttribute是正确的，无需在beforeInvokingHandlerMethod中进行设置.假设您有一个映射到/data/init的方法，该方法将请求转发到/data/custom.在这种情况下，也可以在init方法中设置请求属性.
You are correct in assumption of @RequestAttribute, it need not be set in beforeInvokingHandlerMethod. Assume you have a method mapped to /data/init which forwards request to /data/custom. In this case request attribute can be set in init method also.
为什么在custom()方法之前调用beforeInvokingHandlerMethod()?
Why the beforeInvokingHandlerMethod() is called before the custom() method?
为什么@ModelAttribute批注会注释beforeInvokingHandlerMethod()?在这种情况下是什么意思?
And why the beforeInvokingHandlerMethod() is annoted by @ModelAttribute annotation? what means in this case?
you will get the reason here http://static.springsource.org/spring/docs/3.1.x/spring-framework-reference/html/mvc.html#mvc-ann-modelattrib-methods
方法上的@ModelAttribute指示该方法的目的是添加一个或多个模型属性.此类方法支持与@RequestMapping方法相同的参数类型，但不能直接映射到请求.而是在同一控制器内的@RequestMapping方法之前调用控制器中的@ModelAttribute方法.
An @ModelAttribute on a method indicates the purpose of that method is to add one or more model attributes. Such methods support the same argument types as @RequestMapping methods but cannot be mapped directly to requests. Instead @ModelAttribute methods in a controller are invoked before @RequestMapping methods, within the same controller.
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