详解Spring Controller autowired Request变量


            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";

 }

 }

 





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