spring中如何做到将状态域进行分离出来

在SpringMVC中我们无需显示的获取Request，Session等对象而可以进行直接获取使用

重要的接口和类：

public interface RequestAttributes {

     int SCOPE_REQUEST = 0;

     int SCOPE_SESSION = 1;

     int SCOPE_GLOBAL_SESSION = 2;

    String REFERENCE_REQUEST = "request";

   String REFERENCE_SESSION = "session";

   Object getAttribute(String name, int scope);

    void setAttribute(String name, Object value, int scope);

   void removeAttribute(String name, int scope);

   String[] getAttributeNames(int scope);

   String getSessionId();

   ......

   }

public abstract class RequestContextHolder  {

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

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

public static void resetRequestAttributes() {
requestAttributesHolder.remove();
inheritableRequestAttributesHolder.remove();
}

public static void setRequestAttributes(RequestAttributes attributes) {
setRequestAttributes(attributes, false);
}

public static RequestAttributes getRequestAttributes() {
RequestAttributes attributes = requestAttributesHolder.get();
if (attributes == null) {
attributes = inheritableRequestAttributesHolder.get();
}
return attributes;
}

.....

}

上面的类主要是把状态域对象用ThreadLocal来保存。在以前我们service层要想使用域对象必须先从Controller层中获取再传递过去。现在SpringMVC框架已经在procesRequest做了封装。它会将当前的request对象和session对象封装到框架中。RequestAttributes previousRequestAttributes = RequestContextHolder.getRequestAttributes();和if (previousRequestAttributes == null || previousRequestAttributes.getClass().equals(ServletRequestAttributes.class)) {

requestAttributes = new ServletRequestAttributes(request);

RequestContextHolder.setRequestAttributes(requestAttributes, this.threadContextInheritable);

}就是对其进行设计。而我们的servic层实在processRequest之后调用的所以我们可以直接获取

主要流程及调用类：

FrameworkServlet中的processRequest

LocaleContext previousLocaleContext = LocaleContextHolder.getLocaleContext();
LocaleContextHolder.setLocaleContext(buildLocaleContext(request), this.threadContextInheritable);


RequestAttributes previousRequestAttributes = RequestContextHolder.getRequestAttributes();
ServletRequestAttributes requestAttributes = null;
if (previousRequestAttributes == null || previousRequestAttributes.getClass().equals(ServletRequestAttributes.class)) {
requestAttributes = new ServletRequestAttributes(request);
RequestContextHolder.setRequestAttributes(requestAttributes, this.threadContextInheritable);
}

doService(request, response);

LocaleContextHolder.setLocaleContext(previousLocaleContext, this.threadContextInheritable);
if (requestAttributes != null) {
RequestContextHolder.setRequestAttributes(previousRequestAttributes, this.threadContextInheritable);
requestAttributes.requestCompleted();
}

DispatchServlet中的doService

request.setAttribute(WEB_APPLICATION_CONTEXT_ATTRIBUTE, getWebApplicationContext());
request.setAttribute(LOCALE_RESOLVER_ATTRIBUTE, this.localeResolver);
request.setAttribute(THEME_RESOLVER_ATTRIBUTE, this.themeResolver);
request.setAttribute(THEME_SOURCE_ATTRIBUTE, getThemeSource());

request.setAttribute(OUTPUT_FLASH_MAP_ATTRIBUTE, new FlashMap());

request.setAttribute(FLASH_MAP_MANAGER_ATTRIBUTE, this.flashMapManager);

doDispatch(request, response);

DispatchServlet中的doDispatch方法

ModelAndView mv;

HandlerExecutionChain mappedHandler = null;

processedRequest = checkMultipart(request);
mappedHandler = getHandler(processedRequest, false);

HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

String method = request.getMethod();

HandlerInterceptor[] interceptors = mappedHandler.getInterceptors();
if (interceptors != null) {
for (int i = 0; i < interceptors.length; i++) {
HandlerInterceptor interceptor = interceptors[i];
if (!interceptor.preHandle(processedRequest, response, mappedHandler.getHandler())) {
triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, null);
return;
}
interceptorIndex = i;
}
}

mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

mv.setViewName(getDefaultViewName(request));

if (interceptors != null) {
for (int i = interceptors.length - 1; i >= 0; i--) {
HandlerInterceptor interceptor = interceptors[i];
 interceptor.postHandle(processedRequest, response, mappedHandler.getHandler(), mv);
}
}

render(mv, processedRequest, response);

triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, null);