笔记：pringMVC执行流程解析

图片来源于网络

1、DispatcherServlet 中央调度器（主要职责就是任务调度，在servlet容器）

<!--使用Spring MVC,配置DispatcherServlet是第一步。DispatcherServlet是一个Servlet,所以可以配置多个DispatcherServlet-->
<!--DispatcherServlet是前置控制器，配置在web.xml文件中的。拦截匹配的请求，Servlet拦截匹配规则要自已定义，把拦截下来的请求，依据某某规则分发到目标Controller(我们写的Action)来处理。-->
<servlet>
<!--在DispatcherServlet的初始化过程中，框架会在web应用的 WEB-INF文件夹下寻找名为[servlet-name]-servlet.xml 的配置文件，生成文件中定义的bean。-->
<servlet-name>springmvc</servlet-name>
<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
<!--指明了配置文件的文件名，不使用默认配置文件名，而使用dispatcher-servlet.xml配置文件。-->
<init-param>
<param-name>contextConfigLocation</param-name>
<!--其中<param-value>**.xml</param-value> 这里可以使用多种写法-->
<!--1、不写,使用默认值:/WEB-INF/<servlet-name>-servlet.xml-->
<!--2、<param-value>/WEB-INF/classes/dispatcher-servlet.xml</param-value>-->
<!--3、<param-value>classpath*:dispatcher-servlet.xml</param-value>-->
<!--4、多个值用逗号分隔-->
<param-value>classpath:springmvc/spring-mvc.xml</param-value>
</init-param>
<!--是启动顺序，让这个Servlet随Servletp容器一起启动。-->
<load-on-startup>1</load-on-startup>
</servlet>

2、HandlerMapping 处理器映射器

请求和负责处理请求方法之间的对应关系的一个映射关系

3、HandlerAdaptor 处理器适配器

HandlerAdapter【HttpRequestHandlerAdapter，SimpleControllerHandlerAdapter，SimpleServletHandlerAdapter，AnnotationMethodHandlerAdapter 】

实际调用处理函数，获得一个ModelAndView。

4、Controller 处理器

处理请求

5、ViewResolver 视图解析器

视图解析

6、View 视图

返回的数据

DispatchServlet中核心代码：

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
HttpServletRequest processedRequest = request;
HandlerExecutionChain mappedHandler = null;
boolean multipartRequestParsed = false;
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
try {
ModelAndView mv = null;
Exception dispatchException = null;
try {
processedRequest = checkMultipart(request);
multipartRequestParsed = (processedRequest != request);
/****
* 1、 HandleMapping 返回一个处理器执行链
*/
mappedHandler = getHandler(processedRequest);
if (mappedHandler == null || mappedHandler.getHandler() == null) {
noHandlerFound(processedRequest, response);
return;
}
/****
* 2、获取HandleAdapter 处理器适配器
*/
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

// Process last-modified header, if supported by the handler.
String method = request.getMethod();
boolean isGet = "GET".equals(method);
if (isGet || "HEAD".equals(method)) {
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;
}
/****
* 3、HandleAdapter 调用具体处理器方法，返回一个ModelAndView
*/
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
applyDefaultViewName(processedRequest, mv);
mappedHandler.applyPostHandle(processedRequest, response, mv);
}
catch (Exception ex) {
dispatchException = ex;
}
catch (Throwable err) {
dispatchException = new NestedServletException("Handler dispatch failed", err);
}
/****
* 4、解析渲染视图
*/
processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
}
catch (Exception ex) {
triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
}
catch (Throwable err) {
triggerAfterCompletion(processedRequest, response, mappedHandler,
new NestedServletException("Handler processing failed", err));
}
finally {
if (asyncManager.isConcurrentHandlingStarted()) {
if (mappedHandler != null) {
mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
}
}
else {
if (multipartRequestParsed) {
cleanupMultipart(processedRequest);
}
}
}
}