详解Spring Controller autowired Request变量

三叶草

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";
 }
 }

如有疑问请留言或者到本站社区交流讨论，感谢阅读，希望能帮助到大家，谢谢大家对本站的支持！