SpringMVC概述

Spring web mvc和Struts2都属于表现层的框架,它是Spring框架的一部分,我们可以从Spring的整体结构中看得出来：

springMVC组件流程

1.DispatcherServlet：中央控制器，把请求给转发到具体的控制类
2.Controller：具体处理请求的控制器
3.handlerMapping：映射处理器，负责映射中央处理器转发给controller时的映射策略
4.ModelAndView：服务层返回的数据和视图层的封装类
5.ViewResolver & View：视图解析器，解析具体的视图

6.Interceptors ：拦截器，负责拦截我们定义的请求然后做处理工作

DispatcherServlet

	protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
		HttpServletRequest processedRequest = request;
		HandlerExecutionChain mappedHandler = null;
		boolean multipartRequestParsed = false;

		//创建当前请求的web异步管理器
		WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);

		try {
			ModelAndView mv = null;
			Exception dispatchException = null;

			try {
				//先检查是否是文件上传的请求，是则转化为MultipartHttpServletRequest
				processedRequest = checkMultipart(request);
				multipartRequestParsed = (processedRequest != request);

				// Determine handler for the current request.
				//判断当前请求该使用哪个处理器来处理
				
				//第一步:由HandlerMapping找到对应的handler
				
				//通过遍历HandlerMapping,以获得handler执行链
				mappedHandler = getHandler(processedRequest, false);
				if (mappedHandler == null || mappedHandler.getHandler() == null) {
					noHandlerFound(processedRequest, response);
					return;
				}

				// Determine handler adapter for the current request.
				//第二步，找到合适的HandlerAdapter，由它来调度执行handler的方法 
				HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

				// Process last-modified header, if supported by the handler.
				String method = request.getMethod();
				boolean isGet = "GET".equals(method);
				//get请求或者head请求
				if (isGet || "HEAD".equals(method)) {
					//获取资源上次被修改的头信息
					long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
					if (logger.isDebugEnabled()) {
						logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified);
					}
					if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
						return;
					}
				}
				
				if (!mappedHandler.applyPreHandle(processedRequest, response)) {
					return;
				}

				// Actually invoke the handler.
				//第三步，执行handler，返回ModelAndView
				mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

				if (asyncManager.isConcurrentHandlingStarted()) {
					return;
				}

				
				applyDefaultViewName(request, mv);
				mappedHandler.applyPostHandle(processedRequest, response, mv);
			}
			catch (Exception ex) {
				dispatchException = ex;
			}
			processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
		}
		catch (Exception ex) {
			triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
		}
		catch (Error err) {
			triggerAfterCompletionWithError(processedRequest, response, mappedHandler, err);
		}
		finally {
			if (asyncManager.isConcurrentHandlingStarted()) {
				// Instead of postHandle and afterCompletion
				if (mappedHandler != null) {
					mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
				}
			}
			else {
				// Clean up any resources used by a multipart request.
				if (multipartRequestParsed) {
					cleanupMultipart(processedRequest);
				}
			}
		}
	}

拦截器

public interface HandlerInterceptor {

	boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception;

	void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception;

	void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception;

}

HandlerAdaptor

public interface HandlerAdapter {

	boolean supports(Object handler);

	ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception;

	long getLastModified(HttpServletRequest request, Object handler);

}

HandlerMapping

public interface HandlerMapping {

	HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception;
}

HandlerExecutionChain(删除了部分代码)

public class HandlerExecutionChain {

	private final Object handler;

	private HandlerInterceptor[] interceptors;

	private List<HandlerInterceptor> interceptorList;

	private int interceptorIndex = -1;

	boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {
		HandlerInterceptor[] interceptors = getInterceptors();
		if (!ObjectUtils.isEmpty(interceptors)) {
			for (int i = 0; i < interceptors.length; i++) {
				HandlerInterceptor interceptor = interceptors[i];
				if (!interceptor.preHandle(request, response, this.handler)) {
					triggerAfterCompletion(request, response, null);
					return false;
				}
				this.interceptorIndex = i;
			}
		}
		return true;
	}

	void applyPostHandle(HttpServletRequest request, HttpServletResponse response, ModelAndView mv) throws Exception {
		HandlerInterceptor[] interceptors = getInterceptors();
		if (!ObjectUtils.isEmpty(interceptors)) {
			for (int i = interceptors.length - 1; i >= 0; i--) {
				HandlerInterceptor interceptor = interceptors[i];
				interceptor.postHandle(request, response, this.handler, mv);
			}
		}
	}

	void triggerAfterCompletion(HttpServletRequest request, HttpServletResponse response, Exception ex)
			throws Exception {

		HandlerInterceptor[] interceptors = getInterceptors();
		if (!ObjectUtils.isEmpty(interceptors)) {
			for (int i = this.interceptorIndex; i >= 0; i--) {
				HandlerInterceptor interceptor = interceptors[i];
				try {
					interceptor.afterCompletion(request, response, this.handler, ex);
				}
				catch (Throwable ex2) {
					logger.error("HandlerInterceptor.afterCompletion threw exception", ex2);
				}
			}
		}
	}

	void applyAfterConcurrentHandlingStarted(HttpServletRequest request, HttpServletResponse response) {
		HandlerInterceptor[] interceptors = getInterceptors();
		if (!ObjectUtils.isEmpty(interceptors)) {
			for (int i = interceptors.length - 1; i >= 0; i--) {
				if (interceptors[i] instanceof AsyncHandlerInterceptor) {
					try {
						AsyncHandlerInterceptor asyncInterceptor = (AsyncHandlerInterceptor) interceptors[i];
						asyncInterceptor.afterConcurrentHandlingStarted(request, response, this.handler);
					}
					catch (Throwable ex) {
						logger.error("Interceptor [" + interceptors[i] + "] failed in afterConcurrentHandlingStarted", ex);
					}
				}
			}
		}
	}

}

HandlerMapping接口的实现（）：
BeanNameUrlHandlerMapping ：通过对比url和bean的name找到对应的对象
SimpleUrlHandlerMapping ：也是直接配置url和对应bean,比BeanNameUrlHandlerMapping功能更多
DefaultAnnotationHandlerMapping :主要是针对注解配置@RequestMapping的(已过时)
RequestMappingHandlerMapping ：取代了上面一个