SpringMVC @SessionAttributes 使用详解以及源码分析

@sessionattributes

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Inherited
@Documented
public @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<String> attributeNames = new HashSet<String>();

    private final Set<Class<?>> attributeTypes = new HashSet<Class<?>>();

    private final Set<String> knownAttributeNames = Collections.synchronizedSet(new HashSet<String>(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.<Class<?>>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<String, ?> 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<String, Object> retrieveAttributes(WebRequest request) {
        Map<String, Object> attributes = new HashMap<String, Object>();
        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);
    }

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