DispatcherServlet类执行流程

1、Dispatcher中的属性：
/** Well-known name for the MultipartResolver object in the bean factory for this namespace. */
public static final String MULTIPART_RESOLVER_BEAN_NAME = "multipartResolver";

/** Well-known name for the LocaleResolver object in the bean factory for this namespace. */
public static final String LOCALE_RESOLVER_BEAN_NAME = "localeResolver";

/** Well-known name for the ThemeResolver object in the bean factory for this namespace. */
public static final String THEME_RESOLVER_BEAN_NAME = "themeResolver";

/**
* Well-known name for the HandlerMapping object in the bean factory for this namespace.
* Only used when "detectAllHandlerMappings" is turned off.
* @see #setDetectAllHandlerMappings
*/
public static final String HANDLER_MAPPING_BEAN_NAME = "handlerMapping";

/**
* Well-known name for the HandlerAdapter object in the bean factory for this namespace.
* Only used when "detectAllHandlerAdapters" is turned off.
* @see #setDetectAllHandlerAdapters
*/
public static final String HANDLER_ADAPTER_BEAN_NAME = "handlerAdapter";

/**
* Well-known name for the HandlerExceptionResolver object in the bean factory for this namespace.
* Only used when "detectAllHandlerExceptionResolvers" is turned off.
* @see #setDetectAllHandlerExceptionResolvers
*/
public static final String HANDLER_EXCEPTION_RESOLVER_BEAN_NAME = "handlerExceptionResolver";

/**
* Well-known name for the RequestToViewNameTranslator object in the bean factory for this namespace.
*/
public static final String REQUEST_TO_VIEW_NAME_TRANSLATOR_BEAN_NAME = "viewNameTranslator";

/**
* Well-known name for the ViewResolver object in the bean factory for this namespace.
* Only used when "detectAllViewResolvers" is turned off.
* @see #setDetectAllViewResolvers
*/
public static final String VIEW_RESOLVER_BEAN_NAME = "viewResolver";

/**
* Well-known name for the FlashMapManager object in the bean factory for this namespace.
*/
public static final String FLASH_MAP_MANAGER_BEAN_NAME = "flashMapManager";

/**
* Request attribute to hold the current web application context.
* Otherwise only the global web app context is obtainable by tags etc.
* @see org.springframework.web.servlet.support.RequestContextUtils#getWebApplicationContext
*/
public static final String WEB_APPLICATION_CONTEXT_ATTRIBUTE = DispatcherServlet.class.getName() + ".CONTEXT";

/**
* Request attribute to hold the current LocaleResolver, retrievable by views.
* @see org.springframework.web.servlet.support.RequestContextUtils#getLocaleResolver
*/
public static final String LOCALE_RESOLVER_ATTRIBUTE = DispatcherServlet.class.getName() + ".LOCALE_RESOLVER";

/**
* Request attribute to hold the current ThemeResolver, retrievable by views.
* @see org.springframework.web.servlet.support.RequestContextUtils#getThemeResolver
*/
public static final String THEME_RESOLVER_ATTRIBUTE = DispatcherServlet.class.getName() + ".THEME_RESOLVER";

/**
* Request attribute to hold the current ThemeSource, retrievable by views.
* @see org.springframework.web.servlet.support.RequestContextUtils#getThemeSource
*/
public static final String THEME_SOURCE_ATTRIBUTE = DispatcherServlet.class.getName() + ".THEME_SOURCE";

/**
* Name of request attribute that holds a read-only {@code Map<String,?>}
* with "input" flash attributes saved by a previous request, if any.
* @see org.springframework.web.servlet.support.RequestContextUtils#getInputFlashMap(HttpServletRequest)
*/
public static final String INPUT_FLASH_MAP_ATTRIBUTE = DispatcherServlet.class.getName() + ".INPUT_FLASH_MAP";

/**
* Name of request attribute that holds the "output" {@link FlashMap} with
* attributes to save for a subsequent request.
* @see org.springframework.web.servlet.support.RequestContextUtils#getOutputFlashMap(HttpServletRequest)
*/
public static final String OUTPUT_FLASH_MAP_ATTRIBUTE = DispatcherServlet.class.getName() + ".OUTPUT_FLASH_MAP";

/**
* Name of request attribute that holds the {@link FlashMapManager}.
* @see org.springframework.web.servlet.support.RequestContextUtils#getFlashMapManager(HttpServletRequest)
*/
public static final String FLASH_MAP_MANAGER_ATTRIBUTE = DispatcherServlet.class.getName() + ".FLASH_MAP_MANAGER";

/** Log category to use when no mapped handler is found for a request. */
public static final String PAGE_NOT_FOUND_LOG_CATEGORY = "org.springframework.web.servlet.PageNotFound";

/**
* Name of the class path resource (relative to the DispatcherServlet class)
* that defines DispatcherServlet's default strategy names.
*/
private static final String DEFAULT_STRATEGIES_PATH = "DispatcherServlet.properties";


/** Additional logger to use when no mapped handler is found for a request. */
protected static final Log pageNotFoundLogger = LogFactory.getLog(PAGE_NOT_FOUND_LOG_CATEGORY);

private static final UrlPathHelper urlPathHelper = new UrlPathHelper();

private static final Properties defaultStrategies;

static {
// Load default strategy implementations from properties file.
// This is currently strictly internal and not meant to be customized
// by application developers.
try {
ClassPathResource resource = new ClassPathResource(DEFAULT_STRATEGIES_PATH, DispatcherServlet.class);
defaultStrategies = PropertiesLoaderUtils.loadProperties(resource);
}
catch (IOException ex) {
throw new IllegalStateException("Could not load 'DispatcherServlet.properties': " + ex.getMessage());
}
}

/** Detect all HandlerMappings or just expect "handlerMapping" bean? */
private boolean detectAllHandlerMappings = true;

/** Detect all HandlerAdapters or just expect "handlerAdapter" bean? */
private boolean detectAllHandlerAdapters = true;

/** Detect all HandlerExceptionResolvers or just expect "handlerExceptionResolver" bean? */
private boolean detectAllHandlerExceptionResolvers = true;

/** Detect all ViewResolvers or just expect "viewResolver" bean? */
private boolean detectAllViewResolvers = true;

/** Perform cleanup of request attributes after include request? */
private boolean cleanupAfterInclude = true;

/** MultipartResolver used by this servlet */
private MultipartResolver multipartResolver;

/** LocaleResolver used by this servlet */
private LocaleResolver localeResolver;

/** ThemeResolver used by this servlet */
private ThemeResolver themeResolver;

/** List of HandlerMappings used by this servlet */
private List<HandlerMapping> handlerMappings;

/** List of HandlerAdapters used by this servlet */
private List<HandlerAdapter> handlerAdapters;

/** List of HandlerExceptionResolvers used by this servlet */
private List<HandlerExceptionResolver> handlerExceptionResolvers;

/** RequestToViewNameTranslator used by this servlet */
private RequestToViewNameTranslator viewNameTranslator;

/** FlashMapManager used by this servlet */
private FlashMapManager flashMapManager;

/** List of ViewResolvers used by this servlet */
private List<ViewResolver> viewResolvers;


2、DispatcherServlet中的方法（get/set方法不列）

（上传图片这么麻烦？不能直接粘贴图片？此处省略）

3、DispatcherServlet中的静态块代码如下
static {
// Load default strategy implementations from properties file.
// This is currently strictly internal and not meant to be customized
// by application developers.
try {
ClassPathResource resource = new ClassPathResource(DEFAULT_STRATEGIES_PATH, DispatcherServlet.class);
defaultStrategies = PropertiesLoaderUtils.loadProperties(resource);
}
catch (IOException ex) {
throw new IllegalStateException("Could not load 'DispatcherServlet.properties': " + ex.getMessage());
}
}
该静态块在DispatcherServlet在初始化或第一次调用时执行，一般用来加载配置文件，DispatcherServlets使用该静态块加载配置文件；
使用上DispatcherServlet中的属性private static final String DEFAULT_STRATEGIES_PATH = "DispatcherServlet.properties";阅读静态块代码可调用了SpringMVC中的抽象类
PropertiesLoaderUtils中的loadProperties方法加载读取配置文件'DispatcherServlet.properties'.

'DispatcherServlet.properties'的配置文件如下：
# Default implementation classes for DispatcherServlet's strategy interfaces.
# Used as fallback when no matching beans are found in the DispatcherServlet context.
# Not meant to be customized by application developers.

org.springframework.web.servlet.LocaleResolver=org.springframework.web.servlet.i18n.AcceptHeaderLocaleResolver

org.springframework.web.servlet.ThemeResolver=org.springframework.web.servlet.theme.FixedThemeResolver

org.springframework.web.servlet.HandlerMapping=org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping,\
org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMapping

org.springframework.web.servlet.HandlerAdapter=org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter,\
org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter,\
org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter

org.springframework.web.servlet.HandlerExceptionResolver=org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerExceptionResolver,\
org.springframework.web.servlet.mvc.annotation.ResponseStatusExceptionResolver,\
org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver

org.springframework.web.servlet.RequestToViewNameTranslator=org.springframework.web.servlet.view.DefaultRequestToViewNameTranslator

org.springframework.web.servlet.ViewResolver=org.springframework.web.servlet.view.InternalResourceViewResolver

org.springframework.web.servlet.FlashMapManager=org.springframework.web.servlet.support.SessionFlashMapManager

1、Controller：处理器/页面控制器，做的是MVC中的C的事情，但控制逻辑转移到前端控制器了，用于对请求进行处理；
2、HandlerMapping：请求到处理器的映射，如果映射成功返回一个HandlerExecutionChain对象（包含一个Handler处理器（页面控制器）对象、多个HandlerInterceptor拦截器）对象；如BeanNameUrlHandlerMapping将URL与Bean名字映射，映射成功的Bean就是此处的处理器；
3、HandlerAdapter：HandlerAdapter将会把处理器包装为适配器，从而支持多种类型的处理器，即适配器设计模式的应用，从而很容易支持很多类型的处理器；如SimpleControllerHandlerAdapter将对实现了Controller接口的Bean进行适配，并且掉处理器的handleRequest方法进行功能处理；
4、ViewResolver：ViewResolver将把逻辑视图名解析为具体的View，通过这种策略模式，很容易更换其他视图技术；如InternalResourceViewResolver将逻辑视图名映射为jsp视图；
5、LocalResover：本地化解析，因为Spring支持国际化，因此LocalResover解析客户端的Locale信息从而方便进行国际化；
6、ThemeResovler：主题解析，通过它来实现一个页面多套风格，即常见的类似于软件皮肤效果；
7、MultipartResolver：文件上传解析，用于支持文件上传；
8、HandlerExceptionResolver：处理器异常解析，可以将异常映射到相应的统一错误界面，从而显示用户友好的界面（而不是给用户看到具体的错误信息）；
9、RequestToViewNameTranslator：当处理器没有返回逻辑视图名等相关信息时，自动将请求URL映射为逻辑视图名；
10、FlashMapManager：用于管理FlashMap的策略接口，FlashMap用于存储一个请求的输出，当进入另一个请求时作为该请求的输入，通常用于重定向场景，后边会细述。

主要是用来设置SpringMVC框架中定义接口的默认实现类


DispatcherServlet类调用的入口方法为doService，代码如下：
/**
* Exposes the DispatcherServlet-specific request attributes and delegates to {@link #doDispatch}
* for the actual dispatching.
*/
@Override
protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
if (logger.isDebugEnabled()) {
String requestUri = urlPathHelper.getRequestUri(request);
String resumed = WebAsyncUtils.getAsyncManager(request).hasConcurrentResult() ? " resumed" : "";
logger.debug("DispatcherServlet with name '" + getServletName() + "'" + resumed +
" processing " + request.getMethod() + " request for [" + requestUri + "]");
}

// Keep a snapshot of the request attributes in case of an include,
// 创建请求属性快照，以便恢复属性
Map<String, Object> attributesSnapshot = null;
if (WebUtils.isIncludeRequest(request)) {
logger.debug("Taking snapshot of request attributes before include");
attributesSnapshot = new HashMap<String, Object>();
Enumeration<?> attrNames = request.getAttributeNames();
while (attrNames.hasMoreElements()) {
String attrName = (String) attrNames.nextElement();
if (this.cleanupAfterInclude || attrName.startsWith("org.springframework.web.servlet")) {
attributesSnapshot.put(attrName, request.getAttribute(attrName));
}
}
}

// Make framework objects available to handlers and view objects.将请求与框架处理对象进行绑定
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());
//SpringMVC3.1引入对象，当post提交数据之后，按F5刷新界面时，会发生重复提交，之后，为了不解决重复提交问题，需要在post提交数据之后
//使用Redirect进行重定向，但是，将会丢失数据，为了解决这一问题，在request中加入一属性，就是FlashMap，FlashMap数据是和request绑定
FlashMap inputFlashMap = this.flashMapManager.retrieveAndUpdate(request, response);
if (inputFlashMap != null) {
request.setAttribute(INPUT_FLASH_MAP_ATTRIBUTE, Collections.unmodifiableMap(inputFlashMap));
}
request.setAttribute(OUTPUT_FLASH_MAP_ATTRIBUTE, new FlashMap());
request.setAttribute(FLASH_MAP_MANAGER_ATTRIBUTE, this.flashMapManager);

try {
//转入doDispatch方法
doDispatch(request, response);
}
finally {
if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
return;
}
//恢复原来的属性
// Restore the original attribute snapshot, in case of an include.
if (attributesSnapshot != null) {
restoreAttributesAfterInclude(request, attributesSnapshot);
}
}
}

DispatcherServlet类核心方法，也是SpringMVC的核心，代码如下
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
HttpServletRequest processedRequest = request;
HandlerExecutionChain mappedHandler = null;
boolean multipartRequestParsed = false;
//获取当前请求的异步处理对象WebAsyncManager，如果不存在，则创建一个异步请求对象关联该请求，异步处理返回结果在一个线程
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);

try {
//定义ModelAndView对象，对象包含属性model/view/cleared（默认属性为flash）
ModelAndView mv = null;
//异常对象
Exception dispatchException = null;

try {
//对请求中的上传文件进行处理
processedRequest = checkMultipart(request);
multipartRequestParsed = processedRequest != request;

// 确定当前请求的处理器/返回值为HandlerExcutionChain（请求执行链）
mappedHandler = getHandler(processedRequest);
if (mappedHandler == null || mappedHandler.getHandler() == null) {
noHandlerFound(processedRequest, response);
return;
}
// 确定当前请求处理程序适配器
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

// 如果处理器支持，在最后修改请求head信息
String method = request.getMethod();
boolean isGet = "GET".equals(method);
if (isGet || "HEAD".equals(method)) {
long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
if (logger.isDebugEnabled()) {
String requestUri = urlPathHelper.getRequestUri(request);
logger.debug("Last-Modified value for [" + requestUri + "] is: " + lastModified);
}
if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
return;
}
}

if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}

try {
//调用处理器处理请求.并将返回处理过程中，创建的ModelAndVIew
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
}
finally {
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
}
//设置返回视图名称
applyDefaultViewName(request, mv);
//执行拦截器中的afterCompletion方法
mappedHandler.applyPostHandle(processedRequest, response, mv);
}
catch (Exception ex) {
dispatchException = ex;
}
//对ModelAndView进行检测处理
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
mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
return;
}
// Clean up any resources used by a multipart request.
if (multipartRequestParsed) {
cleanupMultipart(processedRequest);
}
}
}

总结：DispatcherServlet类的运行流程如下：
doService-doDispatch(
1、检查请求类型，是否包含上传文件，如果存在，则使用上传文件进行处理，并将request进行封装返回
2、获取HandlerExcutionChain执行链，通过调用HandlerMapping实现类，获取HandlerExcutionChain，HandlerExcutionChain包括Handler对象、拦截器组、拦截器集合
3、获取handlerAdapter确定请求处理器，通过getHandler方法获取handlerAdapter对象
4、调用处理器处理请求.并在处理方法中，创建的ModelAndVIew
5、从ModelAndView对象中获取响应界面，设置返回视图名称applyDefaultViewName(request, mv);
6、对返回的ModelAndView进行检测
)