为什么不使用@RequestParam而不是@ModelAttribute

问题描述

限时删除！！

在Spring MVC控制器的POST请求处理方法(用 @RequestMapping 注释)中，您可以通过两种方式(正确吗?)从表单中访问POST-ed的表单值.

In a a POST request handling method (annotated with @RequestMapping) of a Spring MVC controller, you can access the form values POST-ed from the form in two ways (correct?).

您可以使用将所有表单值捆绑在一起的模型对象(命令)类，并使用带注释的参数 @Valid @ModelAttribute 传递表单值.这似乎是处理表格的常用方法.

You can use a model object (command) class that bundles all the form values together and use an argument annotated @Valid @ModelAttributeto pass in the form values. This seems to be the common way of processing forms.

 @RequestMapping(value = { "thing/{thing}/part/" }, method = RequestMethod.POST)
 public String processForm(
    @PathVariable("thing") final String thing,
    @ModelAttribute(value = "command") @Valid final Command command,
    final BindingResult bindingResult) {
    if (!bindingResult.hasErrors()) {
       final String name = command.getName();
       final long time = command.getTime().getTime();

       // Process the form

       return "redirect:" + location;
    } else {
       return "form";
    }
 }

使用 @RequestParam .

您可以使用 @RequestParam 注释单个方法参数.

 @RequestMapping(value = { "thing/{thing}/part/" }, method = RequestMethod.POST)
 public String processForm(
       @PathVariable("thing") final String thing,
       @RequestParam(value = "name", required=true) final String name,
       @RequestParam(value = "time", required=true) final Date time,
      final HttpServletResponse response) {
    // Process the form

    return "redirect:" + location;
 }

为什么使用 @ModelAttribute

既然给创建辅助命令类带来了不便，那为什么还要麻烦使用 @ModelAttribute 呢?使用 @RequestParam 的局限性是什么.

Why Use @ModelAttribute

So why bother using @ModelAttribute, given that it has the inconvenience of having to create an auxiliary command class? What are the limitations of using a @RequestParam.

推荐答案

实际上，至少有四种方式(@ RequestParam，@ ModelAttribute，未注释的Pojo参数和直接来自请求对象)

Actually, there are at least four ways (@RequestParam, @ModelAttribute, an un-annotated Pojo parameter, and straight from the Request object)

使用单个结构化参数的主要原因是，如果结构化数据具有多个字段.比使用多个@RequestParam参数更方便，并且您可以同时验证所有参数.使用@ModelAttributes，您可以轻松地从会话，数据库或flashAttributes中检索单个对象.

The main reason to use a single structured parameter is if you have structured data with several fields. It's more convenient than using several @RequestParam params, and you can validate all at the same time. With @ModelAttributes you can retrieve a single object from session, database, or flashAttributes easily.

您可以将现有实体或Pojo与@ModelAttribute一起使用，而不必创建自定义的表单支持对象.

You can use existing Entities or Pojos with @ModelAttribute, you don't need to create a custom Form Backing Object necessarily.

但是，如果您只有一个或两个参数，则@RequestParam可以.

But ya, if you just have one or two params, then @RequestParam is fine.

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