@ModelAttribute注释,什么时候使用它？

Question

假设我们有一个实体Person,一个控制器PersonController和一个edit.jsp页面(创建一个新的或编辑一个现有的人)

调节器

@RequestMapping(value = "/edit", method = RequestMethod.POST)
public String editPerson(@RequestParam("fname") String fname, Model model) {
    if(fname == null || fname.length() == 0){
        model.addAttribute("personToEditOrCreate", new Person());
    }
    else{
        Person p = personService.getPersonByFirstName(fname);
        model.addAttribute("personToEditOrCreate", p);
    }

    return "persons/edit";
}

@RequestMapping(value = "/save", method = RequestMethod.POST)
public String savePerson(Person person, BindingResult result) {

    personService.savePerson(person);
    return "redirect:/home";
}

文件edit.jsp

<form:form method="post" modelAttribute="personToEditOrCreate" action="save">
    <form:hidden path="id"/> 
    <table>
        <tr>
            <td><form:label path="firstName">First Name</form:label></td>
            <td><form:input path="firstName" /></td>
        </tr>
        <tr>
            <td><form:label path="lastName">Last Name</form:label></td>
            <td><form:input path="lastName" /></td>
        </tr>
        <tr>
            <td><form:label path="money">Money</form:label></td>
            <td><form:input path="money" /></td>
        </tr>
        <tr>
            <td colspan="2">
                <input type="submit" value="Add/Edit Person"/>
            </td>
        </tr>
    </table> 

</form:form>

我尝试上面的代码(不使用savePerson方法中的@ModelAttribute注释,它工作正常.为什么以及何时需要将注释添加到person对象:

@RequestMapping(value = "/save", method = RequestMethod.POST)
public String savePerson(@ModelAttribute("personToEditOrCreate") Person person, BindingResult result) {

    personService.savePerson(person);
    return "redirect:/home";
}

Answer 1

您不需要@ModelAttribute(参数)只使用Bean作为参数

例如,这些处理程序方法适用于这些请求:

@RequestMapping("/a")
void pathA(SomeBean someBean) {
  assertEquals("neil", someBean.getName());
}

GET /a?name=neil

@RequestMapping(value="/a", method=RequestMethod.POST)
void pathAPost(SomeBean someBean) {
  assertEquals("neil", someBean.getName());
}

POST /a
name=neil

使用@ModelAttribute(方法)在每个请求中将默认数据加载到模型中 - 例如从数据库中加载,尤其是在使用时@SessionAttributes.这可以在一个Controller或一个中完成ControllerAdvice:

@Controller
@RequestMapping("/foos")
public class FooController {

  @ModelAttribute("foo")
  String getFoo() {
    return "bar";  // set modelMap["foo"] = "bar" on every request
  }

}

转发到的任何JSP FooController:

${foo} //=bar

要么

@ControllerAdvice
public class MyGlobalData {

  @ModelAttribute("foo")
  String getFoo() {
    return "bar";  // set modelMap["foo"] = "bar" on every request
  }

}

任何JSP:

${foo} //=bar

如果要将(方法)的结果用作默认值,请使用@ModelAttribute(参数):@ModelAttribute

@ModelAttribute("attrib1")
SomeBean getSomeBean() {
  return new SomeBean("neil");  // set modelMap["attrib1"] = SomeBean("neil") on every request
}

@RequestMapping("/a")
void pathA(@ModelAttribute("attrib1") SomeBean someBean) {
  assertEquals("neil", someBean.getName());
}

GET /a

使用@ModelAttribute(参数)获取存储在flash属性中的对象:

@RequestMapping("/a")
String pathA(RedirectAttributes redirectAttributes) {
  redirectAttributes.addFlashAttribute("attrib1", new SomeBean("from flash"));
  return "redirect:/b";
}

@RequestMapping("/b")
void pathB(@ModelAttribute("attrib1") SomeBean someBean) {
  assertEquals("from flash", someBean.getName());
}

GET /a

使用@ModelAttribute(参数)获取存储的对象@SessionAttributes

@Controller
@SessionAttributes("attrib1")
public class Controller1 {

    @RequestMapping("/a")
    void pathA(Model model) {
        model.addAttribute("attrib1", new SomeBean("neil")); //this ends up in session due to @SessionAttributes on controller
    }

    @RequestMapping("/b")
    void pathB(@ModelAttribute("attrib1") SomeBean someBean) {
        assertEquals("neil", someBean.getName());
    }
}

GET /a
GET /b