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@sessionattributes

@Target({ElementType.TYPE})@Retention(RetentionPolicy.RUNTIME)@Inherited@Documentedpublic @interface SessionAttributes {    String[] value() default {};    Class[] types() default {};}

 @sessionattributes注解应用到Controller上面，可以将Model中的属性同步到session当中。

先看一个最基本的方法

@Controller@RequestMapping("/Demo.do")@SessionAttributes(value={"attr1","attr2"})public class Demo {        @RequestMapping(params="method=index")    public ModelAndView index() {        ModelAndView mav = new ModelAndView("index.jsp");        mav.addObject("attr1", "attr1Value");        mav.addObject("attr2", "attr2Value");        return mav;    }        @RequestMapping(params="method=index2")    public ModelAndView index2(@ModelAttribute("attr1")String attr1, @ModelAttribute("attr2")String attr2) {        ModelAndView mav = new ModelAndView("success.jsp");        return mav;    }}

index方法返回一个ModelAndView 其中包括视图index.jsp 和 两个键值放入model当中，在没有加入@sessionattributes注解的时候，放入model当中的键值是request级别的。

现在因为在Controller上面标记了@SessionAttributes(value={"attr1","attr2"}) 那么model中的attr1,attr2会同步到session中，这样当你访问index 然后在去访问index2的时候也会获取这俩个属性的值。

当需要清除session当中的值得时候，我们只需要在controller的方法中传入一个SessionStatus的类型对象 通过调用setComplete方法就可以清除了。

 

@RequestMapping(params="method=index3")　　public ModelAndView index4(SessionStatus status) {　　ModelAndView mav = new ModelAndView("success.jsp");　　status.setComplete();　　return mav;}

 

 

 

 

下面就直接分析代码来看Spring是如可封装的。

首先我们需要看2个类 DefaultSessionAttributeStore和SessionAttributesHandler

DefaultSessionAttributeStore这个类是用来往WebRequest存取数据的工具类，WebRequest是Spring包装的HttpServletRequest，大家理解为普通的HttpServletRequest就行了。

public class DefaultSessionAttributeStore implements SessionAttributeStore {    private String attributeNamePrefix = "";    public void setAttributeNamePrefix(String attributeNamePrefix) {        this.attributeNamePrefix = (attributeNamePrefix != null ? attributeNamePrefix : "");    }    public void storeAttribute(WebRequest request, String attributeName, Object attributeValue) {        Assert.notNull(request, "WebRequest must not be null");        Assert.notNull(attributeName, "Attribute name must not be null");        Assert.notNull(attributeValue, "Attribute value must not be null");        String storeAttributeName = getAttributeNameInSession(request, attributeName);        request.setAttribute(storeAttributeName, attributeValue, WebRequest.SCOPE_SESSION);    }    public Object retrieveAttribute(WebRequest request, String attributeName) {        Assert.notNull(request, "WebRequest must not be null");        Assert.notNull(attributeName, "Attribute name must not be null");        String storeAttributeName = getAttributeNameInSession(request, attributeName);        return request.getAttribute(storeAttributeName, WebRequest.SCOPE_SESSION);    }    public void cleanupAttribute(WebRequest request, String attributeName) {        Assert.notNull(request, "WebRequest must not be null");        Assert.notNull(attributeName, "Attribute name must not be null");        String storeAttributeName = getAttributeNameInSession(request, attributeName);        request.removeAttribute(storeAttributeName, WebRequest.SCOPE_SESSION);    }    protected String getAttributeNameInSession(WebRequest request, String attributeName) {        return this.attributeNamePrefix + attributeName;    }}

 

Spring会为每一个Controller初始化一个SessionAttributesHandler实例,用来记录@SessionAttributes(value={"attr1","attr2"})里面的属性信息，当需要同步model的值时，会先判断是否在SessionAttributes当中定义。

public class SessionAttributesHandler {    private final Set
   
     attributeNames = new HashSet
    
     ();    private final Set
     
      > attributeTypes = new HashSet
      
       >();    private final Set
       
         knownAttributeNames = Collections.synchronizedSet(new HashSet
        
         (4)); private final SessionAttributeStore sessionAttributeStore; public SessionAttributesHandler(Class
          handlerType, SessionAttributeStore sessionAttributeStore) { Assert.notNull(sessionAttributeStore, "SessionAttributeStore may not be null."); this.sessionAttributeStore = sessionAttributeStore; SessionAttributes annotation = AnnotationUtils.findAnnotation(handlerType, SessionAttributes.class); if (annotation != null) { this.attributeNames.addAll(Arrays.asList(annotation.value())); this.attributeTypes.addAll(Arrays.
         
          >asList(annotation.types())); } this.knownAttributeNames.addAll(this.attributeNames); } public boolean hasSessionAttributes() { return ((this.attributeNames.size() > 0) || (this.attributeTypes.size() > 0)); } public boolean isHandlerSessionAttribute(String attributeName, Class
           attributeType) { Assert.notNull(attributeName, "Attribute name must not be null"); if (this.attributeNames.contains(attributeName) || this.attributeTypes.contains(attributeType)) { this.knownAttributeNames.add(attributeName); return true; } else { return false; } } public void storeAttributes(WebRequest request, Map
          
            attributes) { for (String name : attributes.keySet()) { Object value = attributes.get(name); Class
            attrType = (value != null) ? value.getClass() : null; if (isHandlerSessionAttribute(name, attrType)) { this.sessionAttributeStore.storeAttribute(request, name, value); } } } public Map
           
             retrieveAttributes(WebRequest request) { Map
            
              attributes = new HashMap
             
              (); for (String name : this.knownAttributeNames) { Object value = this.sessionAttributeStore.retrieveAttribute(request, name); if (value != null) { attributes.put(name, value); } } return attributes; } public void cleanupAttributes(WebRequest request) { for (String attributeName : this.knownAttributeNames) { this.sessionAttributeStore.cleanupAttribute(request, attributeName); } } Object retrieveAttribute(WebRequest request, String attributeName) { return this.sessionAttributeStore.retrieveAttribute(request, attributeName); }}
             
            
           
          
         
        
       
      
     
    
   

 

 

当我们访问controller中的一个方法时，会调用RequestMappingHandlerAdapter类当中的invokeHandleMethod的方法。

private ModelAndView invokeHandleMethod(HttpServletRequest request,            HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {        ServletWebRequest webRequest = new ServletWebRequest(request, response);        WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);        ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);        ServletInvocableHandlerMethod requestMappingMethod = createRequestMappingMethod(handlerMethod, binderFactory);        ModelAndViewContainer mavContainer = new ModelAndViewContainer();        mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request));        modelFactory.initModel(webRequest, mavContainer, requestMappingMethod);        mavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect);        AsyncWebRequest asyncWebRequest = AsyncWebUtils.createAsyncWebRequest(request, response);        asyncWebRequest.setTimeout(this.asyncRequestTimeout);        final WebAsyncManager asyncManager = AsyncWebUtils.getAsyncManager(request);        asyncManager.setTaskExecutor(this.taskExecutor);        asyncManager.setAsyncWebRequest(asyncWebRequest);        if (asyncManager.hasConcurrentResult()) {            Object result = asyncManager.getConcurrentResult();            mavContainer = (ModelAndViewContainer) asyncManager.getConcurrentResultContext()[0];            asyncManager.clearConcurrentResult();            if (logger.isDebugEnabled()) {                logger.debug("Found concurrent result value [" + result + "]");            }            requestMappingMethod = requestMappingMethod.wrapConcurrentResult(result);        }        requestMappingMethod.invokeAndHandle(webRequest, mavContainer);        if (asyncManager.isConcurrentHandlingStarted()) {            return null;        }        return getModelAndView(mavContainer, modelFactory, webRequest);    }

 

我们看这行代码

modelFactory.initModel(webRequest, mavContainer, requestMappingMethod);

跟进去看源码

public void initModel(NativeWebRequest request, ModelAndViewContainer mavContainer, HandlerMethod handlerMethod)            throws Exception {        Map
   
     attributesInSession = this.sessionAttributesHandler.retrieveAttributes(request);        mavContainer.mergeAttributes(attributesInSession);        invokeModelAttributeMethods(request, mavContainer);        for (String name : findSessionAttributeArguments(handlerMethod)) {            if (!mavContainer.containsAttribute(name)) {                Object value = this.sessionAttributesHandler.retrieveAttribute(request, name);                if (value == null) {                    throw new HttpSessionRequiredException("Expected session attribute '" + name + "'");                }                mavContainer.addAttribute(name, value);            }        }    }
   

 

其中这两句是关键的地方,把session的值取出来全部放入到ModelAndViewContainer当中去，这样我就可以再controller当中的方法中获取了，当然直接从session中拿也是可以的。

Map<String, ?> attributesInSession = this.sessionAttributesHandler.retrieveAttributes(request);

mavContainer.mergeAttributes(attributesInSession);

 

在controller中获取sessionAttributes的只有两种方式。

一、public ModelAndView index2(@ModelAttribute("attr1")String attr1, @ModelAttribute("attr2")String attr2) 

二、public ModelAndView index2(ModelMap map)

这俩种方式的区别是，如果使用@ModelAttribute属性获取值，并且@SessionAttributes注解当中还设置了该属性，当属性为null时会跑出异常，因为这几行代码。

for (String name : findSessionAttributeArguments(handlerMethod)) {            if (!mavContainer.containsAttribute(name)) {                Object value = this.sessionAttributesHandler.retrieveAttribute(request, name);                if (value == null) {                    throw new HttpSessionRequiredException("Expected session attribute '" + name + "'");                }                mavContainer.addAttribute(name, value);            }}

 

 

以上分析的都是取值的过程，那么Spring是如何将Model中的数据同步到session当中的呢。

 

我们看上面invokeHandleMethod方法中最后一句话 return getModelAndView(mavContainer, modelFactory, webRequest); 我们跟进去看源码。

private ModelAndView getModelAndView(ModelAndViewContainer mavContainer,            ModelFactory modelFactory, NativeWebRequest webRequest) throws Exception {        modelFactory.updateModel(webRequest, mavContainer);        if (mavContainer.isRequestHandled()) {            return null;        }        ModelMap model = mavContainer.getModel();        ModelAndView mav = new ModelAndView(mavContainer.getViewName(), model);        if (!mavContainer.isViewReference()) {            mav.setView((View) mavContainer.getView());        }        if (model instanceof RedirectAttributes) {            Map
   
     flashAttributes = ((RedirectAttributes) model).getFlashAttributes();            HttpServletRequest request = webRequest.getNativeRequest(HttpServletRequest.class);            RequestContextUtils.getOutputFlashMap(request).putAll(flashAttributes);        }        return mav;    }
   

 

有一行代码是modelFactory.updateModel(webRequest, mavContainer); 我们在跟进去看源码。

我们看到首先判断一下ModelAndViewContainer中的SessionStatus是否是完成状态，如果是TRUE就清除session中的值，反之将ModelAndViewContainer中的model值设置进去。

public void updateModel(NativeWebRequest request, ModelAndViewContainer mavContainer) throws Exception {                if (mavContainer.getSessionStatus().isComplete()){            this.sessionAttributesHandler.cleanupAttributes(request);        }        else {            this.sessionAttributesHandler.storeAttributes(request, mavContainer.getModel());        }                if (!mavContainer.isRequestHandled()) {            updateBindingResult(request, mavContainer.getModel());        }     }

 

 

看到这里可能还有一个疑问，就是我们的数据时设置到ModelAndView里面的,那么这些数据时如何跑到ModelAndViewContainer当中去的呢，其实是在方法执行完成之后Spring帮我们做的，

具体细节查看 ModelAndViewMethodReturnValueHandler方法中的最后一行代码mavContainer.addAllAttributes(mav.getModel());

public void handleReturnValue(            Object returnValue, MethodParameter returnType,            ModelAndViewContainer mavContainer, NativeWebRequest webRequest)            throws Exception {        if (returnValue == null) {            mavContainer.setRequestHandled(true);            return;        }        ModelAndView mav = (ModelAndView) returnValue;        if (mav.isReference()) {            String viewName = mav.getViewName();            mavContainer.setViewName(viewName);            if (viewName != null && viewName.startsWith("redirect:")) {                mavContainer.setRedirectModelScenario(true);            }        }        else {            View view = mav.getView();            mavContainer.setView(view);            if (view instanceof SmartView) {                if (((SmartView) view).isRedirectView()) {                    mavContainer.setRedirectModelScenario(true);                }            }        }        mavContainer.addAllAttributes(mav.getModel());    }

 

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