在SpringMVC Controller中注入Request成员域

主题

　　在工作中遇到1个问题....我们定义了一个Controller基类,所有Springmvc自定义的controller都继承它....在它内部定义一个@Autowired HttpServletRequest request;可不可以? 能不能从这个对象里取requestParamters和attributes? 多线程之间会不会影响?

思考

初次思考,我想这应该是不行的.为什么呢?

注入bean是在spring容器启动的时候...request的实现类是在tomcat里(我使用的servlet容器是tomcat)....我又没在spring的容器里配置这个bean.注入应该是失败的...

退一步说,就算是成功了....那注入的也就是1个对象而已.每次servlet接受到请求都会重新生成1个request...这明显和之前启动的那个对象不同吧....怎么想都不可能成功...

如果确实是这样的....那就没有这篇文章了....后来实践了一下..发现这个注入是可以的.使用起来取数据也没任何问题....

其实我那个时候debug看了一下,基本就知道为什么可以取到数据了..但是我并不知道原理和Spring(Springmvc)的处理流程...所以现在研究了一下并记录下来...

原理

首先给大家看一下在方法中注入request作为参数和在成员域中注入request的 注入的request对象之间的区别....

成员域注入的时候注入的是1个代理对象.是 AutowireUtils.ObjectFactoryDelegatingInvocationHandler的实例.

方法注入的就是一般tomcat原生的requestFacade对象.

所以这是不同的...

     /**
      * Reflective InvocationHandler for lazy access to the current target object.
      */
     @SuppressWarnings("serial")
     private static class ObjectFactoryDelegatingInvocationHandler implements InvocationHandler, Serializable {

         private final ObjectFactory<?> objectFactory;

         public ObjectFactoryDelegatingInvocationHandler(ObjectFactory<?> objectFactory) {
             this.objectFactory = objectFactory;
         }

         @Override
         public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
             String methodName = method.getName();
             if (methodName.equals("equals")) {
                 // Only consider equal when proxies are identical.
                 return (proxy == args[0]);
             }
             else if (methodName.equals("hashCode")) {
                 // Use hashCode of proxy.
                 return System.identityHashCode(proxy);
             }
             else if (methodName.equals("toString")) {
                 return this.objectFactory.toString();
             }
             try {
                 return method.invoke(this.objectFactory.getObject(), args);
             }
             catch (InvocationTargetException ex) {
                 throw ex.getTargetException();
             }
         }
     }

当代理对象(就是成员域request)的大部分方法被调用的时候,ObjectFactoryDelegatingInvocationHandler会使用objectFactory获取对象(原生request),再调用对象上的方法.

然后我们来看下XmlWebApplicationContext初始化到请求到进入controller里几个对注入request成员域有影响的步骤.

refresh方法和postProcessBeanFactory方法

ApplicationContext的抽象实现类AbstractApplicationContext(基本是所有ac的父类)里定义了ac的refresh方法(包含了使用BeanFactory注入bean)的流程..

 @Override
     public void refresh() throws BeansException, IllegalStateException {
         synchronized (this.startupShutdownMonitor) {
             // Prepare this context for refreshing.
             // 记录开始wac开始初始化的时间,设置激活标记,servlet的相关param设置到env(之前做过1次),校验env中必须的props
             prepareRefresh();

             // Tell the subclass to refresh the internal bean factory.
             // 将旧的BF里的bean删掉,新建1个BF,设置部分属性,加载XML配置文件
             ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

             // Prepare the bean factory for use in this context.
             // 1.设置BF解析bean配置需要用到的一些对象比如env. 2.注册一些BeanPostProcessor比如ApplicationContextAwareProcessor去设置Aware需要的对象
             // 3.忽略一些特定class注入的对象,设置一些特定class注入的对象为指定值
             // 4.将一些env中的properties map当做bean注册到BF中
             prepareBeanFactory(beanFactory);

             try {
                 // Allows post-processing of the bean factory in context subclasses.
                 // 1.设置一个BeanPostProcess为ServletContextAware的实现类注入servlet相关对象
                 // 2.在BF中增加requetsScope等Scope
                 // 3.把servletContext,Config,ServletInitParams,ServletAttribute当做Bean注册到BF中
                 postProcessBeanFactory(beanFactory);

                 // Invoke factory processors registered as beans in the context.
                 // 初始化并调用BeanFactoryPostProcessor
                 invokeBeanFactoryPostProcessors(beanFactory);

                 // Register bean processors that intercept bean creation.
                 // 注册BeanPostProcessors并注册到BF中去
                 registerBeanPostProcessors(beanFactory);

                 // Initialize message source for this context.
                 initMessageSource();

                 // Initialize event multicaster for this context.
                 initApplicationEventMulticaster();

                 // Initialize other special beans in specific context subclasses.
                 onRefresh();

                 // Check for listener beans and register them.
                 registerListeners();

                 // Instantiate all remaining (non-lazy-init) singletons.
                 finishBeanFactoryInitialization(beanFactory);

                 // Last step: publish corresponding event.
                 finishRefresh();
             } catch (BeansException ex) {
                 logger.warn("Exception encountered during context initialization - cancelling refresh attempt", ex);

                 // Destroy already created singletons to avoid dangling resources.
                 destroyBeans();

                 // Reset 'active' flag.
                 cancelRefresh(ex);

                 // Propagate exception to caller.
                 throw ex;
             }
         }
     }

其中有1个模板方法

postProcessBeanFactory(beanFactory);

这个方法允许AbstractApplicationContext的子类覆盖它并实现对BF的定制(这个时候bean的defination路径已经指定了,但是bean还没加载).

AbstractRefreshableWebApplicationContext覆盖了这个方法

     /**
      * Register request/session scopes, a {@link ServletContextAwareProcessor}, etc.
      * 1.设置一个BeanPostProcess为ServletContextAware的实现类注入servlet相关对象
      * 2.在BF中增加requetsScope等Scope
      * 3.把servletContext,Config,ServletInitParams,ServletAttribute当做Bean注册到BF中
      *
      */
     @Override
     protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
         // 设置一个BeanPostProcess为ServletContextAware的实现类注入servlet相关对象
         beanFactory.addBeanPostProcessor(new ServletContextAwareProcessor(this.servletContext, this.servletConfig));
         beanFactory.ignoreDependencyInterface(ServletContextAware.class);
         beanFactory.ignoreDependencyInterface(ServletConfigAware.class);

         // 在BF中增加requetsScope等Scope
         WebApplicationContextUtils.registerWebApplicationScopes(beanFactory, this.servletContext);
         // 把servletContext,Config,ServletInitParams,ServletAttribute当做Bean注册到BF中
         WebApplicationContextUtils.registerEnvironmentBeans(beanFactory, this.servletContext, this.servletConfig);
     }

其中有一步

WebApplicationContextUtils.registerWebApplicationScopes(beanFactory, this.servletContext);

这里设置了一些特殊的bean的scope,比如request,session,globalSession,application.(当然这个不是我这篇文章的主题.)

同时设置了一些特殊的autowired bean

beanFactory.registerResolvableDependency(ServletRequest.class, new RequestObjectFactory());
beanFactory.registerResolvableDependency(ServletResponse.class, new ResponseObjectFactory());
beanFactory.registerResolvableDependency(HttpSession.class, new SessionObjectFactory());
beanFactory.registerResolvableDependency(WebRequest.class, new WebRequestObjectFactory());

ServletRequest的实现类(比如HttpServletRequest)被指定使用RequestObjectFactory注入.

RequestObjectFactory

RequestObjectFactory就是1个ObjectFactory就是前面ObjectFactoryDelegatingInvocationHandler里的ObjectFactory.所以在成员域request对象上调用方法其实就是通过RequestObjectFactory获取对象再调用方法.

     /**
      * Factory that exposes the current request object on demand.
      */
     @SuppressWarnings("serial")
     private static class RequestObjectFactory implements ObjectFactory<ServletRequest>, Serializable {

         @Override
         public ServletRequest getObject() {
             return currentRequestAttributes().getRequest();
         }

         @Override
         public String toString() {
             return "Current HttpServletRequest";
         }
     }

     /**
      * Return the current RequestAttributes instance as ServletRequestAttributes.
      *
      * @see RequestContextHolder#currentRequestAttributes()
      */
     private static ServletRequestAttributes currentRequestAttributes() {
         RequestAttributes requestAttr = RequestContextHolder.currentRequestAttributes();
         if (!(requestAttr instanceof ServletRequestAttributes)) {
             throw new IllegalStateException("Current request is not a servlet request");
         }
         return (ServletRequestAttributes) requestAttr;
     }

RequestObjectFactory的getObject方法很简单,就是调用静态方法

RequestContextHolder.currentRequestAttributes().getRequest()

RequestContextHolder

     public static RequestAttributes currentRequestAttributes() throws IllegalStateException {
         RequestAttributes attributes = getRequestAttributes();
         if (attributes == null) {
             if (jsfPresent) {
                 attributes = FacesRequestAttributesFactory.getFacesRequestAttributes();
             }
             if (attributes == null) {
                 throw new IllegalStateException("No thread-bound request found: " +
                         "Are you referring to request attributes outside of an actual web request, " +
                         "or processing a request outside of the originally receiving thread? " +
                         "If you are actually operating within a web request and still receive this message, " +
                         "your code is probably running outside of DispatcherServlet/DispatcherPortlet: " +
                         "In this case, use RequestContextListener or RequestContextFilter to expose the current request.");
             }
         }
         return attributes;
     }

     /**
      * Return the RequestAttributes currently bound to the thread.
      * @return the RequestAttributes currently bound to the thread,
      * or {@code null} if none bound
      */
     public static RequestAttributes getRequestAttributes() {
         RequestAttributes attributes = requestAttributesHolder.get();
         if (attributes == null) {
             attributes = inheritableRequestAttributesHolder.get();
         }
         return attributes;
     }

     private static final ThreadLocal<RequestAttributes> requestAttributesHolder =
             new NamedThreadLocal<RequestAttributes>("Request attributes");

     private static final ThreadLocal<RequestAttributes> inheritableRequestAttributesHolder =
             new NamedInheritableThreadLocal<RequestAttributes>("Request context");

上面是一些关键方法

所以最终其实request是从threadlocal中取...

FrameworkServlet

那么request是什么时候设置到threadlocal中去的呢?

是在Springmvc的dispatcherServlet的父类FrameworkServlet里操作的.

     /**
      * Delegate GET requests to processRequest/doService.
      * <p>Will also be invoked by HttpServlet's default implementation of {@code doHead},
      * with a {@code NoBodyResponse} that just captures the content length.
      * @see #doService
      * @see #doHead
      */
     @Override
     protected final void doGet(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {

         processRequest(request, response);
     }

     /**
      * Delegate POST requests to {@link #processRequest}.
      * @see #doService
      */
     @Override
     protected final void doPost(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {

         processRequest(request, response);
     }

不管你是doGet还是doPost还是doXXX方法都是委托processRequest方法去做的.

 /**
      * Process this request, publishing an event regardless of the outcome.
      * <p>The actual event handling is performed by the abstract
      * {@link #doService} template method.
      */
     protected final void processRequest(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {

         long startTime = System.currentTimeMillis();
         Throwable failureCause = null;

         LocaleContext previousLocaleContext = LocaleContextHolder.getLocaleContext();
         LocaleContext localeContext = buildLocaleContext(request);

         RequestAttributes previousAttributes = RequestContextHolder.getRequestAttributes();
         ServletRequestAttributes requestAttributes = buildRequestAttributes(request, response, previousAttributes);

         WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
         asyncManager.registerCallableInterceptor(FrameworkServlet.class.getName(), new RequestBindingInterceptor());

         initContextHolders(request, localeContext, requestAttributes);

         try {
             doService(request, response);
         }
         catch (ServletException ex) {
             failureCause = ex;
             throw ex;
         }
         catch (IOException ex) {
             failureCause = ex;
             throw ex;
         }
         catch (Throwable ex) {
             failureCause = ex;
             throw new NestedServletException("Request processing failed", ex);
         }

         finally {
             resetContextHolders(request, previousLocaleContext, previousAttributes);
             if (requestAttributes != null) {
                 requestAttributes.requestCompleted();
             }

             if (logger.isDebugEnabled()) {
                 if (failureCause != null) {
                     this.logger.debug("Could not complete request", failureCause);
                 }
                 else {
                     if (asyncManager.isConcurrentHandlingStarted()) {
                         logger.debug("Leaving response open for concurrent processing");
                     }
                     else {
                         this.logger.debug("Successfully completed request");
                     }
                 }
             }

             publishRequestHandledEvent(request, response, startTime, failureCause);
         }
     }

其中调用了

initContextHolders(request, localeContext, requestAttributes);

     private void initContextHolders(
             HttpServletRequest request, LocaleContext localeContext, RequestAttributes requestAttributes) {

         if (localeContext != null) {
             LocaleContextHolder.setLocaleContext(localeContext, this.threadContextInheritable);
         }
         if (requestAttributes != null) {
             RequestContextHolder.setRequestAttributes(requestAttributes, this.threadContextInheritable);
         }
         if (logger.isTraceEnabled()) {
             logger.trace("Bound request context to thread: " + request);
         }
     }

就是在这里设置到RequestContextHolder的threadlocal中去的...

小结

1.在controller中注入的request是jdk动态代理对象,ObjectFactoryDelegatingInvocationHandler的实例.当我们调用成员域request的方法的时候其实是调用了objectFactory的getObject()对象的相关方法.这里的objectFactory是RequestObjectFactory.

2.RequestObjectFactory的getObject其实是从RequestContextHolder的threadlocal中去取值的.

3.请求刚进入springmvc的dispatcherServlet的时候会把request相关对象设置到RequestContextHolder的threadlocal中去.