Java Spring MVC 将属性设置为 request/model/modelMap

Spring MVC set attribute to request/model/modelMap

提问by Oleksandr H

I use Spring MVC. I need to add attribute to request or other object. It should be message that will display on screen. For example, if I use pure Servlets I may just:

我使用 Spring MVC。我需要向请求或其他对象添加属性。它应该是将显示在屏幕上的消息。例如，如果我使用纯 Servlets，我可能只是：

request.setAttribute("message", "User deleted");

and than on JSP page

而不是在 JSP 页面上

<div id="message">${message}</div>

but when I try to do something like this in method:

但是当我尝试在方法中做这样的事情时：

@RequestMapping(value = "/delete", method = RequestMethod.GET)
public String deleteUser(@RequestParam("login") String login,
        ModelMap map, HttpServletRequest request)

Model object -

模型对象 -

model.addAttribute("message", "User deleted");

Map -

地图 -

map.put("message", "User deleted");

ModelMap -

模型图 -

map.put("message", "User deleted");

HttpServletRequest -

HttpServletRequest -

request.setAttribute("message", "User deleted");

nothing displays. But in my browser I see: http:// localhost : 8081 /project/index?message=User+deleted

没有显示。但在我的浏览器中，我看到： http:// localhost : 8081 /project/index?message=User+deleted

How to solve this little problem? Thanks for your answers

这个小问题怎么解决？谢谢你的回答

Updated:

更新：

for clear understanding I try to do this:

为了清楚地理解，我尝试这样做：

 @RequestMapping(value = "/delete", method = RequestMethod.GET)
public String deleteUser(@RequestParam("login") String login,
        Model model) {
    dao.delete(login); // there is NO exeptions
    map.addAttribute("message", "User " + login + " deleted");
    return "redirect:" + "index";
}

in my JSP I also display user login this way:

在我的 JSP 中，我也以这种方式显示用户登录信息：

${user.login}

it takes user from Session and I see it login

它从会话中获取用户，我看到它登录

采纳答案by Sotirios Delimanolis

With your new information, the problem is redirect:. When you do a redirect, you send an HTTP response with a 302 (or 301) response code with a Locationheader pointing to the new url. The browser will make a new HTTP request to that location. As such, your request attributes (and model attributes) are no longer good, they don't exist in the newrequest.

有了你的新信息，问题是redirect:。当您进行重定向时，您会发送一个带有 302（或 301）响应代码的 HTTP 响应，其中包含一个Location指向新 url的标头。浏览器将向该位置发出新的 HTTP 请求。因此，您的请求属性（和模型属性）不再好，它们不存在于新请求中。

Consider use flash attributes. The RedirectAttributesclass is the way to go. The javadoc has a good example.

考虑使用 flash 属性。该RedirectAttributes班是要走的路。javadoc 有一个很好的例子。

---

---

A Modelattribute is added to the request attributes much later during request processing. You therefore won't see it directly doing this

Model稍后在请求处理期间将属性添加到请求属性中。因此，您不会直接看到它这样做

@RequestMapping(value = "/delete", method = RequestMethod.GET)
public String deleteUser(@RequestParam("login") String login,
        ModelMap map, HttpServletRequest request)
    map.put("message", "User deleted");
    String message = (String) request.getAttribute("message"); // will return null
    ...
}

Just trust that it will eventually be in the request attributes and therefore available in your jsp.

只要相信它最终会在请求属性中，因此在您的 jsp 中可用。

回答by Debojit Saikia

As you are redirectingto a new URL, browser is actually sending a new request to the redirect URL. And the request attribute map.addAttribute("message", "User " + login + " deleted");is not present in the new request.

当您redirecting访问一个新 URL 时，浏览器实际上是在向redirect URL. 并且请求属性map.addAttribute("message", "User " + login + " deleted");不存在于新请求中。

You can use RedirectAttributesto show the messageto the user:

您可以使用RedirectAttributes向message用户显示：

@RequestMapping(value = "/delete", method = RequestMethod.GET)
public String deleteUser(@RequestParam("login") String login,
        Model model,RedirectAttributes redirectAttributes) {
    dao.delete(login); // there is NO exeptions
    //map.addAttribute("message", "User " + login + " deleted");
    redirectAttributes.addFlashAttribute("message", "User " + login + " deleted");
    return "redirect:" + "index";
}

redirectAttributes.addAttributeconstructs request parameters out of your attributes and redirects to the desired page with the request parameters. And addFlashAttributestores the attributes in a flashmap (maintained in the users session and removed once the next redirected request gets fulfilled).

redirectAttributes.addAttribute从您的属性中构造请求参数，并使用请求参数重定向到所需的页面。并将addFlashAttribute属性存储在 flashmap 中（在用户会话中维护并在下一个重定向请求得到满足后删除）。

回答by Jimmy

You are redirecting it in a wrong way. instead of return "redirect:"+"index" use return "redirect:/index". redirect it to your get method. as redirectattributes are post/redirect/get attribute. try this and you will get a flash message on your screen. instead of Model use Redirectattributes.

您以错误的方式重定向它。而不是 return "redirect:"+"index" 使用 return "redirect:/index"。将其重定向到您的 get 方法。因为重定向属性是 post/redirect/get 属性。试试这个，你会在屏幕上收到一条闪现信息。而不是模型使用重定向属性。

redirectAttributes.addFlashAttribute("errormsg", "errormessage"); return "redirect:/index.do";

redirectAttributes.addFlashAttribute("errormsg", "errormessage"); 返回“重定向：/index.do”；