详解Spring Controller autowired Request变量

技术  /  管理员 发布于 7年前   158

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

1. 首先request和用户请求相关
2. 不同的用户同时访问时是在不同的线程中
3. 保存了用户的请求在threadlocal中
4. 用户获取该请求需要手动调用threadlocal来获取
5. 为了帮助用户减少重复代码，spring可以让用户‘动态'注入request
6. 当controller在实例化时，动态注册一个proxy到当前request变量中
7. 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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