SpringMVC @SessionAttributes 使用

 @SessionAttributes 只能作用在类上,作用是将指定的Model中的键值对添加至session中,方便在下一次请求中使用。

简单示例

  • 目标是通过 @SessionAttributes 注解将Model中attrName为 "user","age","name" 的值添加至 session 中
 1 @Controller
 2 @RequestMapping("/testSessionAttribute")
 3 @SessionAttributes(value = {"user","age","name"})
 4 public class TestSessionAttributeController {
 5 
 6     @ModelAttribute("user")
 7     public User addUser(){
 8         User user = new User();
 9         user.setName("James");
10         user.setAge(29);
11         return user;
12     }
13 
14     @RequestMapping("/testHandler")
15     public String testHandler(Model model, String age, String name){
16         model.addAttribute("age",age);
17         model.addAttribute("name",name);
18         System.out.println(age);
19         System.out.println(name);
20         return "result";
21     }
22 }

对应的jsp代码如下:

1 <body>
2     ${sessionScope.user.age}
3     ${sessionScope.user.name}
4     <br/>
5     ${sessionScope.age}
6     ${sessionScope.name}
7 </body>

 

通过实例可以得出一下结论:

  1. 不论是利用@ModelAttribute添加至model的数据,还是手动添加至model的数据,均遵循 @SessionAttributes 的规则

清除@SessionAttributes向session中添加的值

如果需要清除通过@SessionAttribute添加至 session 中的数据,则需要在controller 的 handler method中添加 SessionStatus参数,在方法体中调用SessionStatus#setComplete。

需要注意的是,此时清除的只是该Controller通过@SessionAttribute添加至session的数据(当然,如果不同controller的@SessionAttribute拥有相同的值,则也会清除)

 

@Controller
@RequestMapping("/testSessionAttribute")
@SessionAttributes(value = {"user","age","name"})
public class TestSessionAttributeController {

  ..........................  

    @RequestMapping("/removeSessionAttributes")
    public String removeSessionAttributes(SessionStatus sessionStatus){
        sessionStatus.setComplete();
        return "result";
    }
}

通过@ModelAttributes和@SessionAttributes共同添加至session中的数据,只会添加一次

在没用使用SessionStatus清除过之前,通过@ModelAttributes和@SessionAttributes共同添加至session中的数据并不会更新,如下例:

 1 @Controller
 2 @RequestMapping("/testSessionAttribute")
 3 @SessionAttributes(value = {"user","age","name"})
 4 public class TestSessionAttributeController {
 5 
 6     public static int age = 29;
 7     @ModelAttribute("user")
 8     public User addUser(){
 9         User user = new User();
10         user.setName("James");
11         user.setAge(age++);
12         return user;
13     }
14 
15     @RequestMapping("/testHandler")
16     public String testHandler(Model model, String age, String name){
17         model.addAttribute("age",age);
18         model.addAttribute("name",name);
19         System.out.println(age);
20         System.out.println(name);
21         return "result";
22     }
23 
24 }

 

 

1 <body>
2     ${sessionScope.user.age}
3     ${sessionScope.user.name}
4     <br/>
5     ${sessionScope.age}
6     ${sessionScope.name}
7 </body>

 

第一次请求:http://localhost:8080/testSessionAttribute/testHandler.action?name=James&age=29

结果:

29 James 
29 James

第二次请求:http://localhost:8080/testSessionAttribute/testHandler.action?name=James&age=30

29 James 
30 James

原因是,在org.springframework.web.bind.annotation.support.HandlerMethodInvoker#invokeHandlerMethod中进行了如下操作:

 1 public final Object invokeHandlerMethod(Method handlerMethod, Object handler,
 2             NativeWebRequest webRequest, ExtendedModelMap implicitModel) throws Exception {
 3 
 4         Method handlerMethodToInvoke = BridgeMethodResolver.findBridgedMethod(handlerMethod);
 5         try {
 6             boolean debug = logger.isDebugEnabled();
 7             for (String attrName : this.methodResolver.getActualSessionAttributeNames()) {
 8                 Object attrValue = this.sessionAttributeStore.retrieveAttribute(webRequest, attrName);
 9                 if (attrValue != null) {
10                     implicitModel.addAttribute(attrName, attrValue);
11                 }
12             }
13             for (Method attributeMethod : this.methodResolver.getModelAttributeMethods()) {
14                 Method attributeMethodToInvoke = BridgeMethodResolver.findBridgedMethod(attributeMethod);
15                 Object[] args = resolveHandlerArguments(attributeMethodToInvoke, handler, webRequest, implicitModel);
16                 if (debug) {
17                     logger.debug("Invoking model attribute method: " + attributeMethodToInvoke);
18                 }
19                 String attrName = AnnotationUtils.findAnnotation(attributeMethod, ModelAttribute.class).value();
20                 if (!"".equals(attrName) && implicitModel.containsAttribute(attrName)) {
21                     continue;
22                 }
23                 ReflectionUtils.makeAccessible(attributeMethodToInvoke);
24                 Object attrValue = attributeMethodToInvoke.invoke(handler, args);
25                 if ("".equals(attrName)) {
26                     Class<?> resolvedType = GenericTypeResolver.resolveReturnType(attributeMethodToInvoke, handler.getClass());
27                     attrName = Conventions.getVariableNameForReturnType(attributeMethodToInvoke, resolvedType, attrValue);
28                 }
29                 if (!implicitModel.containsAttribute(attrName)) {
30                     implicitModel.addAttribute(attrName, attrValue);
31                 }
32             }
33             Object[] args = resolveHandlerArguments(handlerMethodToInvoke, handler, webRequest, implicitModel);
34             if (debug) {
35                 logger.debug("Invoking request handler method: " + handlerMethodToInvoke);
36             }
37             ReflectionUtils.makeAccessible(handlerMethodToInvoke);
38             return handlerMethodToInvoke.invoke(handler, args);
39         }
40         catch (IllegalStateException ex) {
41             // Internal assertion failed (e.g. invalid signature):
42             // throw exception with full handler method context...
43             throw new HandlerMethodInvocationException(handlerMethodToInvoke, ex);
44         }
45         catch (InvocationTargetException ex) {
46             // User-defined @ModelAttribute/@InitBinder/@RequestMapping method threw an exception...
47             ReflectionUtils.rethrowException(ex.getTargetException());
48             return null;
49         }
50     }

 

 如8-11行所示,在执行被@ModelAttributes注解的方法前,会将上一次通过@SessionAttributes添加至session中的数据添加添加至model中;

第20-22行,在执行被@ModelAttributes注解的方法前,springMVC会判断model中是否已经包含了@ModelAttributes给出的attrName,如果包含,则被@ModelAttributes注解的方法则不再执行

 

posted @ 2019-01-21 22:00  canger  阅读(5907)  评论(0编辑  收藏