详解Spring Controller autowired Request变量
spring的DI大家比较熟悉了，对于依赖注入的实现也无须赘述。
那么spring的bean的默认scope为singleton，对于controller来说每次方法中均可以获得request还是比较有意思的。
对于方法参数上的request通过构建方法的参数可以获得最新的request
public final Object invokeForRequest(NativeWebRequest request, ModelAndViewContainer mavContainer, Object... providedArgs) throws Exception { Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs); if (logger.isTraceEnabled()) { StringBuilder sb = new StringBuilder("Invoking ["); sb.append(getBeanType().getSimpleName()).append("."); sb.append(getMethod().getName()).append("] method with arguments "); sb.append(Arrays.asList(args)); logger.trace(sb.toString()); } Object returnValue = invoke(args); if (logger.isTraceEnabled()) { logger.trace("Method [" + getMethod().getName() + "] returned [" + returnValue + "]"); } return returnValue; }
2. 对于controller等单实例变量来说如何动态注入变量呢？spring使用了很聪明的办法
首先request和用户请求相关
不同的用户同时访问时是在不同的线程中
保存了用户的请求在threadlocal中
用户获取该请求需要手动调用threadlocal来获取
为了帮助用户减少重复代码，spring可以让用户‘动态'注入request
当controller在实例化时，动态注册一个proxy到当前request变量中
此proxy当被使用是可以将所有方法动态路由到threadlocal中该request变量上执行
/** * Register web-specific scopes ("request", "session", "globalSession", "application") * with the given BeanFactory, as used by the WebApplicationContext. * @param beanFactory the BeanFactory to configure * @param sc the ServletContext that we're running within */ public static void registerWebApplicationScopes(ConfigurableListableBeanFactory beanFactory, ServletContext sc) { beanFactory.registerScope(WebApplicationContext.SCOPE_REQUEST, new RequestScope()); beanFactory.registerScope(WebApplicationContext.SCOPE_SESSION, new SessionScope(false)); beanFactory.registerScope(WebApplicationContext.SCOPE_GLOBAL_SESSION, new SessionScope(true)); if (sc != null) { ServletContextScope appScope = new ServletContextScope(sc); beanFactory.registerScope(WebApplicationContext.SCOPE_APPLICATION, appScope); // Register as ServletContext attribute, for ContextCleanupListener to detect it. sc.setAttribute(ServletContextScope.class.getName(), appScope); } beanFactory.registerResolvableDependency(ServletRequest.class, new RequestObjectFactory()); beanFactory.registerResolvableDependency(HttpSession.class, new SessionObjectFactory()); beanFactory.registerResolvableDependency(WebRequest.class, new WebRequestObjectFactory()); if (jsfPresent) { FacesDependencyRegistrar.registerFacesDependencies(beanFactory); } }
/** * Factory that exposes the current request object on demand. */ @SuppressWarnings("serial") private static class RequestObjectFactory implements ObjectFactory<ServletRequest>, Serializable { public ServletRequest getObject() { return currentRequestAttributes().getRequest(); } @Override public String toString() { return "Current HttpServletRequest"; } }