Spring注解@SessionAttributes如何工作

Question

我是Spring的新手，所以如果我的問題很愚蠢，請原諒我。

我無法在我的Spring控制器中使用@SessionAttributes（以及@ModelAttribute）。 我究竟做錯了什么？ 這是代碼...

@Controller
@SessionAttributes("myAttribute")
public class MyController {

@ModelAttribute("myAttribute")
public String createMySessionAttribute() {
    System.out.println("Inside of createMySessionAttribute");
    return new String("mySessionAttribute");
}

//......

@RequestMapping("/doSomething.do")
public ModelAndView doSomething(HttpSession session, HttpServletRequest request) {

    String sessionAttribute = (String)session.getAttribute("myAttribute");
    String requestAttribute = (String)request.getAttribute("myAttribute");
    String requestSessionAttribute = (String)request.getSession().getAttribute("myAttribute");

    System.out.println(" sessionAttribute = " + sessionAttribute
            + "; requestAttribute = " + requestAttribute
            + "; requestSessionAttribute = " + requestSessionAttribute 
            );


    ModelAndView modelAndView = new ModelAndView("nextPage");

    return modelAndView;
}
}

這是輸出...

Inside of createMySessionAttribute
sessionAttribute = null; requestAttribute = null; requestSessionAttribute = null 

我期望 ...

Inside of createMySessionAttribute
sessionAttribute = mySessionAttribute; requestAttribute = mySessionAttribute; requestSessionAttribute = mySessionAttribute

請注意，我嘗試從請求，會話和請求的引用中檢索屬性（這可能是多余的）

謝謝

Answer 1

直到請求結束，它才會將值放入會話中。

如果要在doSomething方法中使用myAttribute的值，請執行以下操作：

/* It should have been called @WriteModelAttribute when used like this */
@ModelAttribute("myAttribute")
String writeModelAttribute() {
    return "myAttribute value";
}

/* It should have been called @ReadModelAttribute when used like this */
ModelAndView doSomething(@ModelAttribute("myAttribute") String myAttribute) {
   System.out.println(myAttribute);  //=myAttribute value
   ...
}

請參見@ModelAttribute批注，何時使用？