《Spring技术内幕》笔记-第四章 Spring MVC与web环境
上下文在web容器中的启动
1，IoC容器的启动过程
IoC的启动过程就是建立上下文的过程。该上下文是与ServletContext相伴。在Spring中存在一个核心控制分发器，DispatcherServlet，这是Spring的核心。在web容器启动Spring应用程序时。首先建立根上下文，然后ContextLoader建立WebApplicationContext。
Web容器中启动Spring步骤例如以下：
在web.xml中。已经配置了ContextLoadListener，该类实现了ServletLoaderListener接口。
ServletLoaderListener是在Servlet API中定义的接口，接口提供Servlet生命周期。而详细的IoC加载过程是ContextLoadListener交由ContextLoader完毕，ContextLoader是ContextLoadListener的父类。三者关系例如以下：
在ContextLoader中。完毕了两个IoC建立的基本过程，一是在Web容器中建立起双亲IoC容器，还有一个是生成对应的WebApplicationContext并将其初始化。
2。Web容器中的上下文设计。
Spring为Web提供了上下文扩展接口WebApplicationContext来满足启动过程的须要。
该接口主要提供getServletContext方法，通过这种方法能够获取容器的Web上下文。
/**
* Return the standard Servlet API ServletContext for this application.
* <p>Also available for a Portlet application, in addition to the PortletContext.
*/
ServletContext getServletContext();
在启动过程中，Spring使用XmlWebApplicationContext作为默认的实现。
XmlWebApplicationContext定义了一系列常量，定义了默认的配置文件，文件位置以及文件类型。
/** Default config location for the root context */
public static final String DEFAULT_CONFIG_LOCATION = "/WEB-INF/applicationContext.xml";
/** Default prefix for building a config location for a namespace */
public static final String DEFAULT_CONFIG_LOCATION_PREFIX = "/WEB-INF/";
/** Default suffix for building a config location for a namespace */
public static final String DEFAULT_CONFIG_LOCATION_SUFFIX = ".xml";
通时。该类的方法中。定义了通过xml启动IoC的过程：
@Override
protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
// Create a new XmlBeanDefinitionReader for the given BeanFactory.
XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
// Configure the bean definition reader with this context's
// resource loading environment.
beanDefinitionReader.setEnvironment(getEnvironment());
beanDefinitionReader.setResourceLoader(this);
beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
// Allow a subclass to provide custom initialization of the reader,
// then proceed with actually loading the bean definitions.
initBeanDefinitionReader(beanDefinitionReader);
loadBeanDefinitions(beanDefinitionReader);
}
完毕对配置文件的读取：
protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws IOException {
String[] configLocations = getConfigLocations();
if (configLocations != null) {
for (String configLocation : configLocations) {
reader.loadBeanDefinitions(configLocation);
}
}
}
获取配置文件位置。
protected String[] getDefaultConfigLocations() {
if (getNamespace() != null) {
return new String[] {DEFAULT_CONFIG_LOCATION_PREFIX + getNamespace() + DEFAULT_CONFIG_LOCATION_SUFFIX};
}
else {
return new String[] {DEFAULT_CONFIG_LOCATION};
}
}
XmlWebApplicationContext类代码中能够看到，该类仅仅是实现了基础的基于XML文件的部分操作。详细的Servlet上下文，则默认取自其父类。
3。ContextLoader的设计与实现
ContextLoaderListener通过ContextLoader完毕IoC的初始化。
ContextLoaderListener的详细实现思路例如以下：ContextLoaderListener监听器启动根IoC容器并把它加载到Web容器的主要功能模块，这也是这个SpringWeb应用加载IoC的第一个地方。
从加载过程能够看到，首先从Servelt事件中得到ServletContext，然后能够读取配置在web.xml中的各个相关属性。记着ContextLoader会实例化WebApplicationContext，并完毕其加载和初始化过程。这个被初始化的第一个上下文作为根上下文存在，这个根上下文加载后。被绑定到Web应用程序的ServletCOntext上。怎样须要訪问根上下文的应用程序代码都能够通过WebApplicationContextUtils类的静态方法中得到。该根上下文存储至：ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE
在ContextLoaderListener中，会监听ServletContext的详细变化，如创建和销毁，并再监听器中定义了对应的回调方法。
public ContextLoaderListener(WebApplicationContext context) {
super(context);
}
/**
* Initialize the root web application context.
*/
@Override
public void contextInitialized(ServletContextEvent event) {
initWebApplicationContext(event.getServletContext());
}
/**
* Close the root web application context.
*/
@Override
public void contextDestroyed(ServletContextEvent event) {
closeWebApplicationContext(event.getServletContext());
ContextCleanupListener.cleanupAttributes(event.getServletContext());
}
详细的调用。交由ContextLoader实现。例如以下。ContextLoader的初始化容器方法：
/**
* Initialize Spring's web application context for the given servlet context,
* using the application context provided at construction time, or creating a new one
* according to the "{@link #CONTEXT_CLASS_PARAM contextClass}" and
* "{@link #CONFIG_LOCATION_PARAM contextConfigLocation}" context-params.
* @param servletContext current servlet context
* @return the new WebApplicationContext
* @see #ContextLoader(WebApplicationContext)
* @see #CONTEXT_CLASS_PARAM
* @see #CONFIG_LOCATION_PARAM
*/
public WebApplicationContext initWebApplicationContext(ServletContext servletContext) {
if (servletContext.getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE) != null) {//是否已存在根上下文
throw new IllegalStateException(
"Cannot initialize context because there is already a root application context present - " +
"check whether you have multiple ContextLoader* definitions in your web.xml!");
}
Log logger = LogFactory.getLog(ContextLoader.class);
servletContext.log("Initializing Spring root WebApplicationContext");
if (logger.isInfoEnabled()) {
logger.info("Root WebApplicationContext: initialization started");
}
long startTime = System.currentTimeMillis();
try {
// Store context in local instance variable, to guarantee that
// it is available on ServletContext shutdown.
if (this.context == null) {//创建上下文
this.context = createWebApplicationContext(servletContext);
}
if (this.context instanceof ConfigurableWebApplicationContext) {
ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) this.context;
if (!cwac.isActive()) {
// The context has not yet been refreshed -> provide services such as
// setting the parent context, setting the application context id, etc
if (cwac.getParent() == null) {
// The context instance was injected without an explicit parent ->
// determine parent for root web application context, if any.加载双亲上下文
ApplicationContext parent = loadParentContext(servletContext);
cwac.setParent(parent);
}
//配置各项參数。以及对应的初始化方法
configureAndRefreshWebApplicationContext(cwac, servletContext);
}
}
servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context);
ClassLoader ccl = Thread.currentThread().getContextClassLoader();
if (ccl == ContextLoader.class.getClassLoader()) {
currentContext = this.context;
}
else if (ccl != null) {
currentContextPerThread.put(ccl, this.context);
}
if (logger.isDebugEnabled()) {
logger.debug("Published root WebApplicationContext as ServletContext attribute with name [" +
WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE + "]");
}
if (logger.isInfoEnabled()) {
long elapsedTime = System.currentTimeMillis() - startTime;
logger.info("Root WebApplicationContext: initialization completed in " + elapsedTime + " ms");
}
return this.context;
}
catch (RuntimeException ex) {
logger.error("Context initialization failed", ex);
servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, ex);
throw ex;
}
catch (Error err) {
logger.error("Context initialization failed", err);
servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, err);
throw err;
}
}
createWebApplicationContext是详细的创建根上下文的方法。
创建好上下文的后。调用了configureAndRefreshWebApplicationContext方法：
protected WebApplicationContext createWebApplicationContext(ServletContext sc) {
Class<?> contextClass = determineContextClass(sc);//Return the WebApplicationContext implementation class to use
if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) {
throw new ApplicationContextException("Custom context class [" + contextClass.getName() +
"] is not of type [" + ConfigurableWebApplicationContext.class.getName() + "]");
}
return (ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
}
protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac, ServletContext sc) {
if (ObjectUtils.identityToString(wac).equals(wac.getId())) {
// The application context id is still set to its original default value
// -> assign a more useful id based on available information
String idParam = sc.getInitParameter(CONTEXT_ID_PARAM);
if (idParam != null) {
wac.setId(idParam);
}
else {
// Generate default id...
wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +
ObjectUtils.getDisplayString(sc.getContextPath()));
}
}
wac.setServletContext(sc);
String configLocationParam = sc.getInitParameter(CONFIG_LOCATION_PARAM);
if (configLocationParam != null) {
wac.setConfigLocation(configLocationParam);
}
// The wac environment's #initPropertySources will be called in any case when the context
// is refreshed; do it eagerly here to ensure servlet property sources are in place for
// use in any post-processing or initialization that occurs below prior to #refresh
ConfigurableEnvironment env = wac.getEnvironment();
if (env instanceof ConfigurableWebEnvironment) {
((ConfigurableWebEnvironment) env).initPropertySources(sc, null);
}
customizeContext(sc, wac);
wac.refresh();
}
determineContextClass方法中。详细了详细实现什么上下文对象。默觉得XmlWebApplicationContext。
protected Class<?> determineContextClass(ServletContext servletContext) {
//配置參数
String contextClassName = servletContext.getInitParameter(CONTEXT_CLASS_PARAM);
if (contextClassName != null) {
try {
return ClassUtils.forName(contextClassName, ClassUtils.getDefaultClassLoader());
}
catch (ClassNotFoundException ex) {
throw new ApplicationContextException(
"Failed to load custom context class [" + contextClassName + "]", ex);
}
}
else {//没有额外配置则採用默认的配置
contextClassName = defaultStrategies.getProperty(WebApplicationContext.class.getName());
try {
return ClassUtils.forName(contextClassName, ContextLoader.class.getClassLoader());
}
catch (ClassNotFoundException ex) {
throw new ApplicationContextException(
"Failed to load default context class [" + contextClassName + "]", ex);
}
}
}
以上就是IoC容器在Web容器中的启动过程，与应用中启动IoC基本同样，唯一不同的是须要考虑web容器特点。设置相应web容器须要的參数。
Spring MVC的设计与实现
Spring MVC出了配置ContextListener之类，还需配置核心分发器DispatcherServlet。DispatcherServlet作为一个前端控制器，全部web请求都要经过他来处理，其对请求进行转发。匹配，数据处理后。再由页面处理。DispatcherServlet是Spring MVC的核心。
1，概览
完毕ContextLoaderListener初始化之后，Web容器開始初始化DispatcherServlet。DispatcherServlet会建立自己的上下文来持有Spring MVC的Bean对象。在建立自己的上下文时，会从ServletContext中得到根上下文作为DispatcherServlet持有的上下文的双亲上下文。有了根上下文。在对自己持有上下文进行初始化，最后把自己的上下文保存到ServletContex，供以后使用。
DispatcherServlet继承自FramworkServlet，FramworkServlet继承HttpServletBean。HttpServletBean继承HttpServlet，通过Servlet API对请求对应。
DispatcherServlet的工作大致分为两个：-1，初始化部分。由initServletBean启动。通过initWebApplicationContext()方法终于抵用DispatcherServlet的initStraegies方法，在这种方法里，DispatcherServlet对MVC的其它模块进行了初始化。比方handlerMapping，ViewResolver。-2，对HTTP请求进行响应。作为一个Servlet，Web容器会调用Servlet的doGet和doPost方法，在经过FraeWorkServlet处理后。会调用DispatcherServlet的doService()方法，这种方法中封装了doDispatch()方法，doDispatch()是DIspatcher实现MVC的主要部分。
2。DispatcherServlet的启动和初始化
DispatcherServlet的初始化方法的開始。是由HttpServletBean的init()方法開始的。该方法负责获取相应的各项配置參数：
/**
* Map config parameters onto bean properties of this servlet, and
* invoke subclass initialization.
* @throws ServletException if bean properties are invalid (or required
* properties are missing), or if subclass initialization fails.
*/
@Override
public final void init() throws ServletException {
if (logger.isDebugEnabled()) {
logger.debug("Initializing servlet '" + getServletName() + "'");
}
// Set bean properties from init parameters.
try {
PropertyValues pvs = new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);
BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
ResourceLoader resourceLoader = new ServletContextResourceLoader(getServletContext());
bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, getEnvironment()));
initBeanWrapper(bw);
bw.setPropertyValues(pvs, true);
}
catch (BeansException ex) {
logger.error("Failed to set bean properties on servlet '" + getServletName() + "'", ex);
throw ex;
}
// Let subclasses do whatever initialization they like.
initServletBean();
if (logger.isDebugEnabled()) {
logger.debug("Servlet '" + getServletName() + "' configured successfully");
}
}
在该方法中。调用了子类的initServletBean()方法，即FrameworkServlet中的initServletBean()方法：
/**
* Overridden method of {@link HttpServletBean}, invoked after any bean properties
* have been set. Creates this servlet's WebApplicationContext.
*/
@Override
protected final void initServletBean() throws ServletException {
getServletContext().log("Initializing Spring FrameworkServlet '" + getServletName() + "'");
if (this.logger.isInfoEnabled()) {
this.logger.info("FrameworkServlet '" + getServletName() + "': initialization started");
}
long startTime = System.currentTimeMillis();
try {//初始化上下文
this.webApplicationContext = initWebApplicationContext();
initFrameworkServlet();
}
catch (ServletException ex) {
this.logger.error("Context initialization failed", ex);
throw ex;
}
catch (RuntimeException ex) {
this.logger.error("Context initialization failed", ex);
throw ex;
}
if (this.logger.isInfoEnabled()) {
long elapsedTime = System.currentTimeMillis() - startTime;
this.logger.info("FrameworkServlet '" + getServletName() + "': initialization completed in " +
elapsedTime + " ms");
}
}
该方法中，通过initWebApplicationContext()完毕初始化上下文操作：
protected WebApplicationContext initWebApplicationContext() {
WebApplicationContext rootContext =
WebApplicationContextUtils.getWebApplicationContext(getServletContext());
WebApplicationContext wac = null;
if (this.webApplicationContext != null) {
// A context instance was injected at construction time -> use it
wac = this.webApplicationContext;
if (wac instanceof ConfigurableWebApplicationContext) {
ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac;
if (!cwac.isActive()) {
// The context has not yet been refreshed -> provide services such as
// setting the parent context, setting the application context id, etc
if (cwac.getParent() == null) {
// The context instance was injected without an explicit parent -> set
// the root application context (if any; may be null) as the parent
cwac.setParent(rootContext);
}
configureAndRefreshWebApplicationContext(cwac);
}
}
}
if (wac == null) {
// No context instance was injected at construction time -> see if one
// has been registered in the servlet context. If one exists, it is assumed
// that the parent context (if any) has already been set and that the
// user has performed any initialization such as setting the context id
wac = findWebApplicationContext();
}
if (wac == null) {
// No context instance is defined for this servlet -> create a local one
wac = createWebApplicationContext(rootContext);
}
if (!this.refreshEventReceived) {
// Either the context is not a ConfigurableApplicationContext with refresh
// support or the context injected at construction time had already been
// refreshed -> trigger initial onRefresh manually here.
onRefresh(wac);
}
if (this.publishContext) {
// Publish the context as a servlet context attribute.
String attrName = getServletContextAttributeName();
getServletContext().setAttribute(attrName, wac);
if (this.logger.isDebugEnabled()) {
this.logger.debug("Published WebApplicationContext of servlet '" + getServletName() +
"' as ServletContext attribute with name [" + attrName + "]");
}
}
return wac;
}
通过WebApplicationContextUtils.getWebApplicationContext获取根上下文。
public static WebApplicationContext getWebApplicationContext(ServletContext sc) {
return getWebApplicationContext(sc, WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE);
}
public static WebApplicationContext getWebApplicationContext(ServletContext sc, String attrName) {
Assert.notNull(sc, "ServletContext must not be null");
Object attr = sc.getAttribute(attrName);
if (attr == null) {
return null;
}
if (attr instanceof RuntimeException) {
throw (RuntimeException) attr;
}
if (attr instanceof Error) {
throw (Error) attr;
}
if (attr instanceof Exception) {
throw new IllegalStateException((Exception) attr);
}
if (!(attr instanceof WebApplicationContext)) {
throw new IllegalStateException("Context attribute is not of type WebApplicationContext: " + attr);
}
return (WebApplicationContext) attr;
}
建立好根上下文后，在通过createWebApplicationContext建立DispatcherServlet的上下文。
protected WebApplicationContext createWebApplicationContext(ApplicationContext parent) {
Class<?> contextClass = getContextClass();
if (this.logger.isDebugEnabled()) {
this.logger.debug("Servlet with name '" + getServletName() +
"' will try to create custom WebApplicationContext context of class '" +
contextClass.getName() + "'" + ", using parent context [" + parent + "]");
}
if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) {
throw new ApplicationContextException(
"Fatal initialization error in servlet with name '" + getServletName() +
"': custom WebApplicationContext class [" + contextClass.getName() +
"] is not of type ConfigurableWebApplicationContext");
}
ConfigurableWebApplicationContext wac =
(ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
wac.setEnvironment(getEnvironment());
wac.setParent(parent);
wac.setConfigLocation(getContextConfigLocation());
configureAndRefreshWebApplicationContext(wac);
return wac;
}
再通过configureAndRefreshWebApplicationContext完毕各项配置以及初始化：
protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac) {
if (ObjectUtils.identityToString(wac).equals(wac.getId())) {
// The application context id is still set to its original default value
// -> assign a more useful id based on available information
if (this.contextId != null) {
wac.setId(this.contextId);
}
else {
// Generate default id...
wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +
ObjectUtils.getDisplayString(getServletContext().getContextPath()) + "/" + getServletName());
}
}
wac.setServletContext(getServletContext());
wac.setServletConfig(getServletConfig());
wac.setNamespace(getNamespace());
wac.addApplicationListener(new SourceFilteringListener(wac, new ContextRefreshListener()));
// The wac environment's #initPropertySources will be called in any case when the context
// is refreshed; do it eagerly here to ensure servlet property sources are in place for
// use in any post-processing or initialization that occurs below prior to #refresh
ConfigurableEnvironment env = wac.getEnvironment();
if (env instanceof ConfigurableWebEnvironment) {
((ConfigurableWebEnvironment) env).initPropertySources(getServletContext(), getServletConfig());
}
postProcessWebApplicationContext(wac);
applyInitializers(wac);
wac.refresh();//初始化
}
以上完毕了DispatcherServlet的IoC容器的建立。
在Spring MVC DispatcherServlet的初始化过程中。以对HandlerMapping的初始化作为開始。该初始化过程。以HttpServletbean的init方法開始，到FrameWorkServlet的initServletBean，再到DispatcherServlet的onRefresh方法。最后到initStrategies()，启动整个MVC的初始化。
/**
* This implementation calls {@link #initStrategies}.
*/
@Override
protected void onRefresh(ApplicationContext context) {
initStrategies(context);
}
/**
* Initialize the strategy objects that this servlet uses.
* <p>May be overridden in subclasses in order to initialize further strategy objects.
*/
protected void initStrategies(ApplicationContext context) {
initMultipartResolver(context);
initLocaleResolver(context);
initThemeResolver(context);
initHandlerMappings(context);
initHandlerAdapters(context);
initHandlerExceptionResolvers(context);
initRequestToViewNameTranslator(context);
initViewResolvers(context);
initFlashMapManager(context);
}
HandlerMappings的初始化例如以下：
private void initHandlerMappings(ApplicationContext context) {
this.handlerMappings = null;
if (this.detectAllHandlerMappings) {
// Find all HandlerMappings in the ApplicationContext, including ancestor contexts.
Map<String, HandlerMapping> matchingBeans =
BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false);
if (!matchingBeans.isEmpty()) {
this.handlerMappings = new ArrayList<HandlerMapping>(matchingBeans.values());
// We keep HandlerMappings in sorted order.
OrderComparator.sort(this.handlerMappings);
}
}
else {
try {
HandlerMapping hm = context.getBean(HANDLER_MAPPING_BEAN_NAME, HandlerMapping.class);
this.handlerMappings = Collections.singletonList(hm);
}
catch (NoSuchBeanDefinitionException ex) {
// Ignore, we'll add a default HandlerMapping later.
}
}
// Ensure we have at least one HandlerMapping, by registering
// a default HandlerMapping if no other mappings are found.
if (this.handlerMappings == null) {
this.handlerMappings = getDefaultStrategies(context, HandlerMapping.class);
if (logger.isDebugEnabled()) {
logger.debug("No HandlerMappings found in servlet '" + getServletName() + "': using default");
}
}
}
以上即为HandlerMappings的读取过程。
MVC处理HTTP分发请求
1。HandlerMapping的配置和设计原理
在初始化完毕时。在上下文环境中已经定义的全部HandlerMapping都已经被载入了，这些HandlerMapping被放入List并排序。存储着HTTP请求的相应映射数据。Spring提供了一系列HandlerMapping实现。SimpleUrlHandlerMapping为例。在SimpleUrlHandlerMapping中定义了一个Map持有一系列的映射关系，这些映射关系使SpringMVC能够相应到Controller中。
这些映射关系通过HandlerMapping接口封装。通过getHandler获取相应的HandlerExcutionChain，在HandlerExcutionChain中封装详细的Controller。
HandlerMapping接口的方法例如以下：
HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception;
此处是典型的命令模式。
HandlerExecutionChain中持有一个Inteceptor链和一个handler对象。该handler实际就是Controller对象。
public class HandlerExecutionChain {
private static final Log logger = LogFactory.getLog(HandlerExecutionChain.class);
private final Object handler;
private HandlerInterceptor[] interceptors;
private List<HandlerInterceptor> interceptorList;
private int interceptorIndex = -1;
构造函数：
/**
* Create a new HandlerExecutionChain.
* @param handler the handler object to execute
* @param interceptors the array of interceptors to apply
* (in the given order) before the handler itself executes
*/
public HandlerExecutionChain(Object handler, HandlerInterceptor[] interceptors) {
if (handler instanceof HandlerExecutionChain) {
HandlerExecutionChain originalChain = (HandlerExecutionChain) handler;
this.handler = originalChain.getHandler();
this.interceptorList = new ArrayList<HandlerInterceptor>();
CollectionUtils.mergeArrayIntoCollection(originalChain.getInterceptors(), this.interceptorList);
CollectionUtils.mergeArrayIntoCollection(interceptors, this.interceptorList);
}
else {
this.handler = handler;
this.interceptors = interceptors;
}
}
HandlerExecutionChain中定义的Handler和Interceptor须要在定义HandlerMapping的时候配置好。
以SimpleUrlHandlerMapping为例。
在初始化时。会调用。
/**
* Calls the {@link #registerHandlers} method in addition to the
* superclass's initialization.
*/
@Override
public void initApplicationContext() throws BeansException {
super.initApplicationContext();
registerHandlers(this.urlMap);
}
/**
* Register all handlers specified in the URL map for the corresponding paths.
* @param urlMap Map with URL paths as keys and handler beans or bean names as values
* @throws BeansException if a handler couldn't be registered
* @throws IllegalStateException if there is a conflicting handler registered
*/
protected void registerHandlers(Map<String, Object> urlMap) throws BeansException {
if (urlMap.isEmpty()) {
logger.warn("Neither 'urlMap' nor 'mappings' set on SimpleUrlHandlerMapping");
}
else {
for (Map.Entry<String, Object> entry : urlMap.entrySet()) {
String url = entry.getKey();
Object handler = entry.getValue();
// Prepend with slash if not already present.
if (!url.startsWith("/")) {
url = "/" + url;
}
// Remove whitespace from handler bean name.
if (handler instanceof String) {
handler = ((String) handler).trim();
}
registerHandler(url, handler);
}
}
}
部分发放基于其父类，AbstractUrlhandlerMapping。
/**
* Register the specified handler for the given URL path.
* @param urlPath the URL the bean should be mapped to
* @param handler the handler instance or handler bean name String
* (a bean name will automatically be resolved into the corresponding handler bean)
* @throws BeansException if the handler couldn't be registered
* @throws IllegalStateException if there is a conflicting handler registered
*/
protected void registerHandler(String urlPath, Object handler) throws BeansException, IllegalStateException {
Assert.notNull(urlPath, "URL path must not be null");
Assert.notNull(handler, "Handler object must not be null");
Object resolvedHandler = handler;
// Eagerly resolve handler if referencing singleton via name.
if (!this.lazyInitHandlers && handler instanceof String) {
String handlerName = (String) handler;
if (getApplicationContext().isSingleton(handlerName)) {
resolvedHandler = getApplicationContext().getBean(handlerName);
}
}
Object mappedHandler = this.handlerMap.get(urlPath);
if (mappedHandler != null) {
if (mappedHandler != resolvedHandler) {
throw new IllegalStateException(
"Cannot map " + getHandlerDescription(handler) + " to URL path [" + urlPath +
"]: There is already " + getHandlerDescription(mappedHandler) + " mapped.");
}
}
else {
if (urlPath.equals("/")) {
if (logger.isInfoEnabled()) {
logger.info("Root mapping to " + getHandlerDescription(handler));
}
setRootHandler(resolvedHandler);
}
else if (urlPath.equals("/*")) {
if (logger.isInfoEnabled()) {
logger.info("Default mapping to " + getHandlerDescription(handler));
}
setDefaultHandler(resolvedHandler);
}
else {
this.handlerMap.put(urlPath, resolvedHandler);
if (logger.isInfoEnabled()) {
logger.info("Mapped URL path [" + urlPath + "] onto " + getHandlerDescription(handler));
}
}
}
}
hadnlerMap保存了URL和controller的映射关系。
private final Map<String, Object> handlerMap = new LinkedHashMap<String, Object>();
2，使用HandlerMapping完毕请求的处理。
在HandlerExecutionChain的启动过程中，调用了getHandler方法，该方法就是完毕请求映射处理的地方。AbstractHadnlerMapping的getHandler方法例如以下：
/**
* Look up a handler for the given request, falling back to the default
* handler if no specific one is found.
* @param request current HTTP request
* @return the corresponding handler instance, or the default handler
* @see #getHandlerInternal
*/
@Override
public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
Object handler = getHandlerInternal(request);
if (handler == null) {
handler = getDefaultHandler();
}
if (handler == null) {
return null;
}
// Bean name or resolved handler?
if (handler instanceof String) {
String handlerName = (String) handler;
handler = getApplicationContext().getBean(handlerName);
}
return getHandlerExecutionChain(handler, request);
}
/**
* Build a {@link HandlerExecutionChain} for the given handler, including
* applicable interceptors.
* <p>The default implementation builds a standard {@link HandlerExecutionChain}
* with the given handler, the handler mapping's common interceptors, and any
* {@link MappedInterceptor}s matching to the current request URL. Subclasses
* may override this in order to extend/rearrange the list of interceptors.
* <p><b>NOTE:</b> The passed-in handler object may be a raw handler or a
* pre-built {@link HandlerExecutionChain}. This method should handle those
* two cases explicitly, either building a new {@link HandlerExecutionChain}
* or extending the existing chain.
* <p>For simply adding an interceptor in a custom subclass, consider calling
* {@code super.getHandlerExecutionChain(handler, request)} and invoking
* {@link HandlerExecutionChain#addInterceptor} on the returned chain object.
* @param handler the resolved handler instance (never {@code null})
* @param request current HTTP request
* @return the HandlerExecutionChain (never {@code null})
* @see #getAdaptedInterceptors()
*/
protected HandlerExecutionChain getHandlerExecutionChain(Object handler, HttpServletRequest request) {
HandlerExecutionChain chain = (handler instanceof HandlerExecutionChain ?
(HandlerExecutionChain) handler : new HandlerExecutionChain(handler));
chain.addInterceptors(getAdaptedInterceptors());
String lookupPath = this.urlPathHelper.getLookupPathForRequest(request);
for (MappedInterceptor mappedInterceptor : this.mappedInterceptors) {
if (mappedInterceptor.matches(lookupPath, this.pathMatcher)) {
chain.addInterceptor(mappedInterceptor.getInterceptor());
}
}
return chain;
}
取得Handler的详细方法在getHandlerInternal()。该方法的详细实如今AbstractUrlHandlerMapping中：
/**
* Look up a handler for the URL path of the given request.
* @param request current HTTP request
* @return the handler instance, or {@code null} if none found
*/
@Override
protected Object getHandlerInternal(HttpServletRequest request) throws Exception {
//从request获取请求路径
String lookupPath = getUrlPathHelper().getLookupPathForRequest(request);
//请求路径与Handler匹配
Object handler = lookupHandler(lookupPath, request);
if (handler == null) {
// We need to care for the default handler directly, since we need to
// expose the PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE for it as well.
Object rawHandler = null;
if ("/".equals(lookupPath)) {
rawHandler = getRootHandler();
}
if (rawHandler == null) {
rawHandler = getDefaultHandler();
}
if (rawHandler != null) {
// Bean name or resolved handler?
if (rawHandler instanceof String) {
String handlerName = (String) rawHandler;
rawHandler = getApplicationContext().getBean(handlerName);
}
validateHandler(rawHandler, request);
handler = buildPathExposingHandler(rawHandler, lookupPath, lookupPath, null);
}
}
if (handler != null && logger.isDebugEnabled()) {
logger.debug("Mapping [" + lookupPath + "] to " + handler);
}
else if (handler == null && logger.isTraceEnabled()) {
logger.trace("No handler mapping found for [" + lookupPath + "]");
}
return handler;
}
/**
* Look up a handler instance for the given URL path.
* <p>Supports direct matches, e.g. a registered "/test" matches "/test",
* and various Ant-style pattern matches, e.g. a registered "/t*" matches
* both "/test" and "/team". For details, see the AntPathMatcher class.
* <p>Looks for the most exact pattern, where most exact is defined as
* the longest path pattern.
* @param urlPath URL the bean is mapped to
* @param request current HTTP request (to expose the path within the mapping to)
* @return the associated handler instance, or {@code null} if not found
* @see #exposePathWithinMapping
* @see org.springframework.util.AntPathMatcher
*/
protected Object lookupHandler(String urlPath, HttpServletRequest request) throws Exception {
// Direct match?
Object handler = this.handlerMap.get(urlPath);
if (handler != null) {
// Bean name or resolved handler?
if (handler instanceof String) {
String handlerName = (String) handler;
handler = getApplicationContext().getBean(handlerName);
}
validateHandler(handler, request);
return buildPathExposingHandler(handler, urlPath, urlPath, null);
}
// Pattern match?
List<String> matchingPatterns = new ArrayList<String>();
for (String registeredPattern : this.handlerMap.keySet()) {
if (getPathMatcher().match(registeredPattern, urlPath)) {
matchingPatterns.add(registeredPattern);
}
}
String bestPatternMatch = null;
Comparator<String> patternComparator = getPathMatcher().getPatternComparator(urlPath);
if (!matchingPatterns.isEmpty()) {
Collections.sort(matchingPatterns, patternComparator);
if (logger.isDebugEnabled()) {
logger.debug("Matching patterns for request [" + urlPath + "] are " + matchingPatterns);
}
bestPatternMatch = matchingPatterns.get(0);
}
if (bestPatternMatch != null) {
handler = this.handlerMap.get(bestPatternMatch);
// Bean name or resolved handler?
if (handler instanceof String) {
String handlerName = (String) handler;
handler = getApplicationContext().getBean(handlerName);
}
validateHandler(handler, request);
String pathWithinMapping = getPathMatcher().extractPathWithinPattern(bestPatternMatch, urlPath);
// There might be multiple 'best patterns', let's make sure we have the correct URI template variables
// for all of them
Map<String, String> uriTemplateVariables = new LinkedHashMap<String, String>();
for (String matchingPattern : matchingPatterns) {
if (patternComparator.compare(bestPatternMatch, matchingPattern) == 0) {
Map<String, String> vars = getPathMatcher().extractUriTemplateVariables(matchingPattern, urlPath);
Map<String, String> decodedVars = getUrlPathHelper().decodePathVariables(request, vars);
uriTemplateVariables.putAll(decodedVars);
}
}
if (logger.isDebugEnabled()) {
logger.debug("URI Template variables for request [" + urlPath + "] are " + uriTemplateVariables);
}
return buildPathExposingHandler(handler, bestPatternMatch, pathWithinMapping, uriTemplateVariables);
}
// No handler found...
return null;
}
经过一系列对HTTP请求进行解析和匹配handler的过程，得到了与请求对一个的handler处理器。在返回的handler中。已经完毕了在HandlerExecutionChain中的封装工作，为handler对HTTP请求的响应做好了准备。
3，Spring对HTTP请求的分发处理。
DispatcherServlet是Servlet的子类，通过doService来响应HTTP请求。
/**
* 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 resumed = WebAsyncUtils.getAsyncManager(request).hasConcurrentResult() ?
" resumed" : "";
logger.debug("DispatcherServlet with name '" + getServletName() + "'" + resumed +
" processing " + request.getMethod() + " request for [" + getRequestUri(request) + "]");
}
// Keep a snapshot of the request attributes in case of an include,
// to be able to restore the original attributes after the include.
Map<String, Object> attributesSnapshot = null;
if (WebUtils.isIncludeRequest(request)) {
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.
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());
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 {
doDispatch(request, response);
}
finally {
if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
return;
}
// Restore the original attribute snapshot, in case of an include.
if (attributesSnapshot != null) {
restoreAttributesAfterInclude(request, attributesSnapshot);
}
}
}
doDispatch方法：
/*** Process the actual dispatching to the handler.* <p>The handler will be obtained by applying the servlet's HandlerMappings in order.* The HandlerAdapter will be obtained by querying the servlet's installed HandlerAdapters* to find the first that supports the handler class.* <p>All HTTP methods are handled by this method. It's up to HandlerAdapters or handlers* themselves to decide which methods are acceptable.* @param request current HTTP request* @param response current HTTP response* @throws Exception in case of any kind of processing failure*/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);// Determine handler for the current request.mappedHandler = getHandler(processedRequest);if (mappedHandler == null || mappedHandler.getHandler() == null) {noHandlerFound(processedRequest, response);return;}// Determine handler adapter for the current request.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;}try {// Actually invoke the handler.mv = ha.handle(processedRequest, response, mappedHandler.getHandler());}finally {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 afterCompletionmappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);return;}// Clean up any resources used by a multipart request.if (multipartRequestParsed) {cleanupMultipart(processedRequest);}}}
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {for (HandlerMapping hm : this.handlerMappings) {if (logger.isTraceEnabled()) {logger.trace("Testing handler map [" + hm + "] in DispatcherServlet with name '" + getServletName() + "'");}HandlerExecutionChain handler = hm.getHandler(request);if (handler != null) {return handler;}}return null;}
protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {for (HandlerAdapter ha : this.handlerAdapters) {if (logger.isTraceEnabled()) {logger.trace("Testing handler adapter [" + ha + "]");}if (ha.supports(handler)) {return ha;}}throw new ServletException("No adapter for handler [" + handler +"]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler");}
HandlerAdapter的基本实现。SimpleControllerHandlerAddapter。
public class SimpleControllerHandlerAdapter implements HandlerAdapter {@Overridepublic boolean supports(Object handler) {return (handler instanceof Controller);}@Overridepublic ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)throws Exception {return ((Controller) handler).handleRequest(request, response);}@Overridepublic long getLastModified(HttpServletRequest request, Object handler) {if (handler instanceof LastModified) {return ((LastModified) handler).getLastModified(request);}return -1L;}}
经过上面的处理。获取到Controller对象，開始调用Handler对象的HTTP响应动作。
运行完获取到视图，并将视图返回。
Spring MVC视图的呈现
1，DispatcherServlet视图呈现设计
在DIspatchServlet的doDispatch()方法中，获取到视图后调用了processDispatchResult()方法处理结果。视图的处理採用render方法。
/*** Render the given ModelAndView.* <p>This is the last stage in handling a request. It may involve resolving the view by name.* @param mv the ModelAndView to render* @param request current HTTP servlet request* @param response current HTTP servlet response* @throws ServletException if view is missing or cannot be resolved* @throws Exception if there's a problem rendering the view*/protected void render(ModelAndView mv, HttpServletRequest request, HttpServletResponse response) throws Exception {// Determine locale for request and apply it to the response.Locale locale = this.localeResolver.resolveLocale(request);response.setLocale(locale);View view;if (mv.isReference()) {// We need to resolve the view name.view = resolveViewName(mv.getViewName(), mv.getModelInternal(), locale, request);if (view == null) {throw new ServletException("Could not resolve view with name '" + mv.getViewName() +"' in servlet with name '" + getServletName() + "'");}}else {// No need to lookup: the ModelAndView object contains the actual View object.view = mv.getView();if (view == null) {throw new ServletException("ModelAndView [" + mv + "] neither contains a view name nor a " +"View object in servlet with name '" + getServletName() + "'");}}// Delegate to the View object for rendering.if (logger.isDebugEnabled()) {logger.debug("Rendering view [" + view + "] in DispatcherServlet with name '" + getServletName() + "'");}try {view.render(mv.getModelInternal(), request, response);}catch (Exception ex) {if (logger.isDebugEnabled()) {logger.debug("Error rendering view [" + view + "] in DispatcherServlet with name '" +getServletName() + "'", ex);}throw ex;}}
resolveViewName通过对视图名称对象解析，获取视图。
protected View resolveViewName(String viewName, Map<String, Object> model, Locale locale,HttpServletRequest request) throws Exception {for (ViewResolver viewResolver : this.viewResolvers) {View view = viewResolver.resolveViewName(viewName, locale);if (view != null) {return view;}}return null;}
ViewResolver的resolveViewName方法，BeanNameViewresolver是其经常使用实现。
@Overridepublic View resolveViewName(String viewName, Locale locale) throws BeansException {ApplicationContext context = getApplicationContext();if (!context.containsBean(viewName)) {// Allow for ViewResolver chaining.return null;}return context.getBean(viewName, View.class);}
Spring为了实现视图的灵活性，方便应用使用各种视图。在View接口下实现了不同View对象。各View对象依据其详细的使用，氛围不同的视图。
2，JSP视图的实现
使用jsp作为视图，Sprinng採用JstlView来作为View对象，而其render方法继承自父类AbstractView。
/*** Prepares the view given the specified model, merging it with static* attributes and a RequestContext attribute, if necessary.* Delegates to renderMergedOutputModel for the actual rendering.* @see #renderMergedOutputModel*/@Overridepublic void render(Map<String, ?> model, HttpServletRequest request, HttpServletResponse response) throws Exception {if (logger.isTraceEnabled()) {logger.trace("Rendering view with name '" + this.beanName + "' with model " + model +" and static attributes " + this.staticAttributes);}Map<String, Object> mergedModel = createMergedOutputModel(model, request, response);prepareResponse(request, response);renderMergedOutputModel(mergedModel, request, response);}
createMergedOutputModel方法：
/*** Creates a combined output Map (never {@code null}) that includes dynamic values and static attributes.* Dynamic values take precedence over static attributes.*/protected Map<String, Object> createMergedOutputModel(Map<String, ?> model, HttpServletRequest request,HttpServletResponse response) {@SuppressWarnings("unchecked")Map<String, Object> pathVars = (this.exposePathVariables ?(Map<String, Object>) request.getAttribute(View.PATH_VARIABLES) : null);// Consolidate static and dynamic model attributes.int size = this.staticAttributes.size();size += (model != null) ? model.size() : 0;size += (pathVars != null) ? pathVars.size() : 0;Map<String, Object> mergedModel = new LinkedHashMap<String, Object>(size);mergedModel.putAll(this.staticAttributes);if (pathVars != null) {mergedModel.putAll(pathVars);}if (model != null) {mergedModel.putAll(model);}// Expose RequestContext?if (this.requestContextAttribute != null) {mergedModel.put(this.requestContextAttribute, createRequestContext(request, response, mergedModel));}return mergedModel;}
renderMergedOutputModel，在InternalResourceView中完毕，InternalResourceView也属于JstlView的基类。
/*** Render the internal resource given the specified model.* This includes setting the model as request attributes.*/@Overrideprotected void renderMergedOutputModel(Map<String, Object> model, HttpServletRequest request, HttpServletResponse response) throws Exception {// Determine which request handle to expose to the RequestDispatcher.HttpServletRequest requestToExpose = getRequestToExpose(request);// Expose the model object as request attributes.exposeModelAsRequestAttributes(model, requestToExpose);// Expose helpers as request attributes, if any.exposeHelpers(requestToExpose);// Determine the path for the request dispatcher.String dispatcherPath = prepareForRendering(requestToExpose, response);// Obtain a RequestDispatcher for the target resource (typically a JSP).RequestDispatcher rd = getRequestDispatcher(requestToExpose, dispatcherPath);if (rd == null) {throw new ServletException("Could not get RequestDispatcher for [" + getUrl() +"]: Check that the corresponding file exists within your web application archive!");}// If already included or response already committed, perform include, else forward.if (useInclude(requestToExpose, response)) {response.setContentType(getContentType());if (logger.isDebugEnabled()) {logger.debug("Including resource [" + getUrl() + "] in InternalResourceView '" + getBeanName() + "'");}rd.include(requestToExpose, response);}else {// Note: The forwarded resource is supposed to determine the content type itself.if (logger.isDebugEnabled()) {logger.debug("Forwarding to resource [" + getUrl() + "] in InternalResourceView '" + getBeanName() + "'");}rd.forward(requestToExpose, response);}}
AbstractView的exposeModelAsRequestAttributes()方法：
/*** Expose the model objects in the given map as request attributes.* Names will be taken from the model Map.* This method is suitable for all resources reachable by {@link javax.servlet.RequestDispatcher}.* @param model Map of model objects to expose* @param request current HTTP request*/protected void exposeModelAsRequestAttributes(Map<String, Object> model, HttpServletRequest request) throws Exception {for (Map.Entry<String, Object> entry : model.entrySet()) {String modelName = entry.getKey();Object modelValue = entry.getValue();if (modelValue != null) {request.setAttribute(modelName, modelValue);if (logger.isDebugEnabled()) {logger.debug("Added model object '" + modelName + "' of type [" + modelValue.getClass().getName() +"] to request in view with name '" + getBeanName() + "'");}}else {request.removeAttribute(modelName);if (logger.isDebugEnabled()) {logger.debug("Removed model object '" + modelName +"' from request in view with name '" + getBeanName() + "'");}}}}
/*** Prepare for rendering, and determine the request dispatcher path* to forward to (or to include).* <p>This implementation simply returns the configured URL.* Subclasses can override this to determine a resource to render,* typically interpreting the URL in a different manner.* @param request current HTTP request* @param response current HTTP response* @return the request dispatcher path to use* @throws Exception if preparations failed* @see #getUrl()*/protected String prepareForRendering(HttpServletRequest request, HttpServletResponse response)throws Exception {String path = getUrl();if (this.preventDispatchLoop) {String uri = request.getRequestURI();if (path.startsWith("/") ?
uri.equals(path) : uri.equals(StringUtils.applyRelativePath(uri, path))) {throw new ServletException("Circular view path [" + path + "]: would dispatch back " +"to the current handler URL [" + uri + "] again. Check your ViewResolver setup! " +"(Hint: This may be the result of an unspecified view, due to default view name generation.)");}}return path;}
视图的解析过程大概就例如以下代码。
总而言之。Spring MVC的建立有下面几个过程：
-1。须要建立Controller和HTTP请求之间的映射关系。在HandlerMapping中封装HandlerExecutionChain对象完毕。而对Controller和HTTP请求关系的描写叙述是在Bean定义的描写叙述。并在IoC初始化时。通过初始化HandlerMapping来完毕，这些映射关系存储在handlerMap中。
-2，在MVC接收请求的时候，DispatcherServlet会依据详细的URL请求信息。在HandlerMapping中查询，从而得到HandlerExecutionChain。在HandlerExecutionChain中封装了Controller，这个请求的COntroller会完毕请求对应，以及生成须要的ModelAndView对象。
-3。得到ModelAndView对象后，DispatcherServlet将ModelAndView对象交给特定的视图对象。通过视图对象完毕数据呈现工作。
