SpringMVC是Spring一个非常重要的模块，从大体上看，在使用SpringMVC的时候，需要在web.xml中配置DispatcherServlet，这个DispatcherServlet可以看成是一个前端控制器的实现，web请求会通过它分发给各个对应的Controller，然后会看到ModelAndView数据的生成，并把ModelAndView数据交给对应的View视图来进行呈现。下面我们来对SpringMVC的设计进行详细的分析。
一、根上下文在容器中的启动
SpringMVC作为Spring的一个模块，也是建立在IOC容器的基础上的，首先我们来了解下Spring的IOC容器是如何在Web环境中载入并起作用的。如果要在web环境中使用IOC容器，需要为IOC容器设计一个启动过程，把IOC容器导入，这个启动的过程是与web容器的启动过程集成在一起的，我们以tomcat作为web容器来进行分析。先来看一个SpringMVC相关的web.xml中的配置
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>classpath:/applicationContext.xml</param-value>
</context-param>
<listener>
<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
<servlet>
<servlet-name>dispatcher</servlet-name>
<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
<init-param>
<param-name>contextConfigLocation</param-name>
<param-value>classpath:/spring-mvc.xml</param-value>
</init-param>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>dispatcher</servlet-name>
<url-pattern>/</url-pattern>
</servlet-mapping>在这个web.xml中，定义了一个Servlet对象——DispatcherSerlvet，这个类是SpringMVC的核心类，它的实现原理我们后面再来分析，context-param参数的配置用来指定SpringIOC容器读取Bean定义的xml文件的路径。在这个文件中，一般用来定义Spring应用的Bean配置。最后，我们可以看到一个监听器的配置——ContextLoaderListener，这个类作为SpringMVC的启动类，负责完成IOC容器在web环境中的启动工作，它是与web容器的生命周期相关联的，下面我们来具体看看IOC容器在web容器中的启动过程是如何实现的。
容器的启动过程是与ServletContext相伴而生的，由ContextLoaderListener启动的上下文为根上下文，此外，还有一个与Web MVC相关的上下文用来保存控制器（DispatcherServlet）需要的MVC对象，作为根上下文的子上下文，构成一个层次化的上下文体系。
ContextLoaderListener实现了ServletContextListener接口，这个接口里的函数会结合Web容器的生命周期被调用，因为ServletContextListener是ServletContext的监听者，如果ServletContext发生变化会触发相应的事件，这些事件包括在服务器启动，ServletContext被创建的时候回触发contextInitialized方法；服务关闭时，ServletContext被销毁的时候触发contextDestroyed方法。IOC容器的初始化就是在contextInitialized方法中完成，这个方法的代码如下：
public void contextInitialized(ServletContextEvent event) {
initWebApplicationContext(event.getServletContext());
}initWebApplicationContext方法的具体实现在的ContextLoaderListener父类ContextLoader中
public WebApplicationContext initWebApplicationContext(ServletContext servletContext) {
//如果已经有根上下文存在
if (servletContext.getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE) != null) {
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 {
//初始化上下文
if (this.context == null) {
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
//载入上下文的双亲上下文并设置双亲上下文
if (cwac.getParent() == null) {
// The context instance was injected without an explicit parent ->
// determine parent for root web application context, if any.
ApplicationContext parent = loadParentContext(servletContext);
cwac.setParent(parent);
}
//对上下文的属性进行一些设置并调用refresh方法初始化
configureAndRefreshWebApplicationContext(cwac, servletContext);
}
}
//将上下文对象设置到ServletContext中
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;
}
}首先来看看createWebApplicationContext方法中如何初始化根上下文
protected WebApplicationContext createWebApplicationContext(ServletContext sc) {
//判断作为IOC容器的类的类型
Class<?> contextClass = determineContextClass(sc);
if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) {
throw new ApplicationContextException("Custom context class [" + contextClass.getName() +
"] is not of type [" + ConfigurableWebApplicationContext.class.getName() + "]");
}
//实例化IOC容器
return (ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
}protected Class<?> determineContextClass(ServletContext servletContext) {
//读取对contextClass的配置
String contextClassName = servletContext.getInitParameter(CONTEXT_CLASS_PARAM);
//如果配置了contextClass那么就使用这个配置的class，当然前提是这个class可用
if (contextClassName != null) {
try {
return ClassUtils.forName(contextClassName, ClassUtils.getDefaultClassLoader());
}
catch (ClassNotFoundException ex) {
throw new ApplicationContextException(
"Failed to load custom context class [" + contextClassName + "]", ex);
}
}
//否则使用默认的类，这个默认的上下文的类是org.springframework.web.context.support.XmlWebApplicationContext，
//是在ContextLoader.properties文件中配置的
else {
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);
}
}
}然后看看configureAndRefreshWebApplicationContext方法中对于容器的参数的一些配置，方法代码如下
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()));
}
}
//将ServletContext设置到容器中
wac.setServletContext(sc);
//设置配置文件的位置参数
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);
//调用refresh方法启动容器的初始化
wac.refresh();
}这就是IOC容器在web容器中的启动过程，在初始化这个上下文之后，该上下文会被存储到ServletContext中，这样就建立了一个全局的关于整个应用的根上下文。在后面我们还会看到，在DispatcherServlet进行自己的上下文初始化时，会将这个根上下文设置为DispatcherServlet自带的上下文的双亲上下文。
二、Spring MVC的设计与实现
在前面的web.xml中我们看到，除了配置ContextLoaderListener之外，还要对DispatcherServlet进行配置。DispatcherServlet十分重要，它可以说是Spring MVC实现中最核心的部分，它作为一个前端控制器，所有的web请求都需要通过它来处理，进行转发、匹配、数据处理后，转由页面进行展现，它的设计与分析也是下面分析Spring MVC的一条主线。
DispatcherServlet的工作大致可以分为两个部分：一是初始化部分，DispatcherServlet通过这部分功能对MVC模块的其他部分进行了初始化，比如handlerMapping、ViewResolver等；另一个是对http请求进行响应，DispatcherServlet对请求的转发及处理在这部分功能中完成。
2.1 DispatcherServlet的启动及初始化
我们先来分析DispatcherServlet的初始化过程，作为一个Servlet，DispatcherServlet启动时首先会调用它的init方法，这个方法的实现在它的父类HttpServletBean中，代码如下
public final void init() throws ServletException {
if (logger.isDebugEnabled()) {
logger.debug("Initializing servlet '" + getServletName() + "'");
}
// 获取Servlet的初始化参数，对Bean的属性进行设置
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;
}
// 调用子类的initServletBean方法进行具体的初始化，主要的初始化过程在这个方法中
initServletBean();
if (logger.isDebugEnabled()) {
logger.debug("Servlet '" + getServletName() + "' configured successfully");
}
}initServletBean的实现在DispatcherServlet的父类FrameworkServlet中
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 {
//在这里初始化上下文
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");
}
}protected WebApplicationContext initWebApplicationContext() {
//获取之前在ContextLoaderListener中保存到ServletContext中的根上下文
WebApplicationContext rootContext =
WebApplicationContextUtils.getWebApplicationContext(getServletContext());
WebApplicationContext wac = null;
//如果当前类中的webApplicationContext不为空
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()) {
//将当前根上下文作为双亲上下文
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);
}
//设置上下文的相关属性并调用refresh方法触发初始化
configureAndRefreshWebApplicationContext(cwac);
}
}
}
if (wac == null) {
wac = findWebApplicationContext();
}
if (wac == null) {
//具体的初始化的过程
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);
}
//将当前建立的上下文存到Servletcontext中,属性名为
//org.springframework.web.servlet.FrameworkServlet.CONTEXT.dispatcher
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;
}protected WebApplicationContext createWebApplicationContext(ApplicationContext parent) {
//获取需要初始化的上下文的对应的类，默认是XmlWebApplicationContext
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");
}
//通过反射初始化得到上下文对象
ConfigurableWebApplicationContext wac =
(ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
//设置一些相关的属性并将根上下文设置为双亲上下文，这样一来根上下文中
//的Bean也可以被DispatcherServlet中的上下文使用
wac.setEnvironment(getEnvironment());
wac.setParent(parent);
wac.setConfigLocation(getContextConfigLocation());
//设置相关属性并调用refresh方法进行容器的初始化
configureAndRefreshWebApplicationContext(wac);
return wac;
}configureAndRefreshWebApplicationContext与前面的ContextLoader中的configureAndRefreshWebApplicationContext有些类似
protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac) {
//对上下文的属性进行设置
if (ObjectUtils.identityToString(wac).equals(wac.getId())) {
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()));
ConfigurableEnvironment env = wac.getEnvironment();
if (env instanceof ConfigurableWebEnvironment) {
((ConfigurableWebEnvironment) env).initPropertySources(getServletContext(), getServletConfig());
}
postProcessWebApplicationContext(wac);
applyInitializers(wac);
//调用refresh方法触发容器的初始化
wac.refresh();
}初始化的过程中还会调用DispatcherServlet中的onRefresh方法，onRefresh方法中会调用DispatcherServlet的initStrategies，这个方法会触发整个Spring MVC框架的初始化
protected void onRefresh(ApplicationContext context) {
initStrategies(context);
}protected void initStrategies(ApplicationContext context) {
initMultipartResolver(context);
initLocaleResolver(context);
initThemeResolver(context);
initHandlerMappings(context);
initHandlerAdapters(context);
initHandlerExceptionResolvers(context);
initRequestToViewNameTranslator(context);
initViewResolvers(context);
initFlashMapManager(context);
}对于上面的方法名称，很容易理解。以initHandlerMappings方法为例来看看这个初始化过程，方法代码如下
private void initHandlerMappings(ApplicationContext context) {
//这个handlerMappings是个List，用来存放所有的HandlerMapping
this.handlerMappings = null;
//导入所有的HandlerMapping，detectAllHandlerMappings默认为真，即默认的从所有的IOC容器中取
if (this.detectAllHandlerMappings) {
// 从容器中取得所有的HandlerMapping，包括父级容器，如果配置了<mvc:annotation-driven/>，
//那么这里默认是BeanNameUrlHandlerMapping和RequestMappingHandlerMapping，
//matchingBeans的键分别是它们完整的类名
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.
AnnotationAwareOrderComparator.sort(this.handlerMappings);
}
}
else {//也可以根据名称从当前的IOC容器中取得handlerMapping
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.
}
}
// 如果都没有取到的话，那么从DispatcherServlet.properties中取默认设置的HandlerMapping
if (this.handlerMappings == null) {
this.handlerMappings = getDefaultStrategies(context, HandlerMapping.class);
if (logger.isDebugEnabled()) {
logger.debug("No HandlerMappings found in servlet '" + getServletName() + "': using default");
}
}
}这样，DispatcherServlet就把所有的HandlerMapping初始化到了handlerMapping变量中。其他的初始化过程与HandlerMapping比较类似，都是从IOC容器中读取配置。经过这些过程，DispatcherServlet的初始化就全部完成了。
2.2 SpringMVC的分发请求
在分析SpringMVC对请求的分发之前，我们先来看看HandlerMapping的设计原理，HandlerMapping在SpringMVC分发请求的过程中起着十分重要的作用，一般每个handlerMapping都持有一系列从url请求到Controller的映射，以RequestMappingHandlerMapping为例，RequstMappingHandlerMapping是我们经常会用到的一个HandlerMapping，当我们配置<mvc:annotation-driven/>时，DispatcherServlet中会用它作为HandlerMapping。
RequstMappingHandlerMapping的父类实现了InitializingBean，所以通过getBean实例化它时会调用它的afterPropertiesSet方法，该方法代码如下
public void afterPropertiesSet() {
//实例化一个BuilderConfiguration对象并为它设置一些属性
this.config = new RequestMappingInfo.BuilderConfiguration();
this.config.setUrlPathHelper(getUrlPathHelper());
this.config.setPathMatcher(getPathMatcher());
this.config.setSuffixPatternMatch(this.useSuffixPatternMatch);
this.config.setTrailingSlashMatch(this.useTrailingSlashMatch);
this.config.setRegisteredSuffixPatternMatch(this.useRegisteredSuffixPatternMatch);
this.config.setContentNegotiationManager(getContentNegotiationManager());
//调用父类的afterPropertiesSet方法
super.afterPropertiesSet();
}该方法中会调用它的父类AbstractHandlerMethodMapping中的afterPropertiesSet方法
public void afterPropertiesSet() {
//该方法用来将请求路径与控制器中的方法进行匹配
initHandlerMethods();
}protected void initHandlerMethods() {
if (logger.isDebugEnabled()) {
logger.debug("Looking for request mappings in application context: " + getApplicationContext());
}
//获取上下文对象中所有的beanName
String[] beanNames = (this.detectHandlerMethodsInAncestorContexts ?
BeanFactoryUtils.beanNamesForTypeIncludingAncestors(getApplicationContext(), Object.class) :
getApplicationContext().getBeanNamesForType(Object.class));
//遍历所有的bean
for (String beanName : beanNames) {
if (!beanName.startsWith(SCOPED_TARGET_NAME_PREFIX)) {
Class<?> beanType = null;
try {
//获取它们的类型
beanType = getApplicationContext().getType(beanName);
}
catch (Throwable ex) {
// An unresolvable bean type, probably from a lazy bean - let's ignore it.
if (logger.isDebugEnabled()) {
logger.debug("Could not resolve target class for bean with name '" + beanName + "'", ex);
}
}
//判断是否为Controller或者RequestMapping注解，如果是则取得类中处理请求的方法
if (beanType != null && isHandler(beanType)) {
detectHandlerMethods(beanName);
}
}
}
handlerMethodsInitialized(getHandlerMethods());
}protected void detectHandlerMethods(final Object handler) {
//获取类的类型
Class<?> handlerType = (handler instanceof String ?
getApplicationContext().getType((String) handler) : handler.getClass());
final Class<?> userType = ClassUtils.getUserClass(handlerType);
//这个map的key是Controller中的Method,value是RequestMappingInfo,
//MetadataLookup中的方法会在selectMethods中被回调
Map<Method, T> methods = MethodIntrospector.selectMethods(userType,
new MethodIntrospector.MetadataLookup<T>() {
@Override
public T inspect(Method method) {
try {
return getMappingForMethod(method, userType);
}
catch (Throwable ex) {
throw new IllegalStateException("Invalid mapping on handler class [" +
userType.getName() + "]: " + method, ex);
}
}
});
if (logger.isDebugEnabled()) {
logger.debug(methods.size() + " request handler methods found on " + userType + ": " + methods);
}
//遍历methods并注册处理请求的方法
for (Map.Entry<Method, T> entry : methods.entrySet()) {
Method invocableMethod = AopUtils.selectInvocableMethod(entry.getKey(), userType);
T mapping = entry.getValue();
registerHandlerMethod(handler, invocableMethod, mapping);
}
}下面来看看selectMethods中是如何获取到RequestMappingInfo的
public static <T> Map<Method, T> selectMethods(Class<?> targetType, final MetadataLookup<T> metadataLookup) {
final Map<Method, T> methodMap = new LinkedHashMap<Method, T>();
Set<Class<?>> handlerTypes = new LinkedHashSet<Class<?>>();
Class<?> specificHandlerType = null;
//添加处理请求的bean(Controller)
if (!Proxy.isProxyClass(targetType)) {
handlerTypes.add(targetType);
specificHandlerType = targetType;
}
handlerTypes.addAll(Arrays.asList(targetType.getInterfaces()));
//遍历这些bean
for (Class<?> currentHandlerType : handlerTypes) {
final Class<?> targetClass = (specificHandlerType != null ? specificHandlerType : currentHandlerType);
//doWithMethods中会调用MethodCallback的doWith方法对bean中的所有方法进行处理,包括父类的方法
ReflectionUtils.doWithMethods(currentHandlerType, new ReflectionUtils.MethodCallback() {
@Override
public void doWith(Method method) {
Method specificMethod = ClassUtils.getMostSpecificMethod(method, targetClass);
//调用metadataLookup的inspect方法获取RequestioMappingInfo
T result = metadataLookup.inspect(specificMethod);
//将方法添加到map中
if (result != null) {
Method bridgedMethod = BridgeMethodResolver.findBridgedMethod(specificMethod);
if (bridgedMethod == specificMethod || metadataLookup.inspect(bridgedMethod) == null) {
methodMap.put(specificMethod, result);
}
}
}
}, ReflectionUtils.USER_DECLARED_METHODS);
}
return methodMap;
}具体取得RequestMappingInfo的过程在RequestMappingHandlerMapping的getMappingForMethod方法中
protected RequestMappingInfo getMappingForMethod(Method method, Class<?> handlerType) {
RequestMappingInfo info = createRequestMappingInfo(method);
if (info != null) {
RequestMappingInfo typeInfo = createRequestMappingInfo(handlerType);
if (typeInfo != null) {
info = typeInfo.combine(info);
}
}
return info;
}private RequestMappingInfo createRequestMappingInfo(AnnotatedElement element) {
RequestMapping requestMapping = AnnotatedElementUtils.findMergedAnnotation(element, RequestMapping.class);
RequestCondition<?> condition = (element instanceof Class<?> ?
getCustomTypeCondition((Class<?>) element) : getCustomMethodCondition((Method) element));
//这里是真正生成RequestMappingHandlerMapping的地方
return (requestMapping != null ? createRequestMappingInfo(requestMapping, condition) : null);
}protected RequestMappingInfo createRequestMappingInfo(
RequestMapping requestMapping, RequestCondition<?> customCondition) {
//这里使用建造者模式构造RequestMappingHandlerMapping,build方法的实现在
return RequestMappingInfo
.paths(resolveEmbeddedValuesInPatterns(requestMapping.path()))
.methods(requestMapping.method())
.params(requestMapping.params())
.headers(requestMapping.headers())
.consumes(requestMapping.consumes())
.produces(requestMapping.produces())
.mappingName(requestMapping.name())
.customCondition(customCondition)
.options(this.config)
.build();
}public RequestMappingInfo build() {
ContentNegotiationManager manager = this.options.getContentNegotiationManager();
PatternsRequestCondition patternsCondition = new PatternsRequestCondition(
this.paths, this.options.getUrlPathHelper(), this.options.getPathMatcher(),
this.options.useSuffixPatternMatch(), this.options.useTrailingSlashMatch(),
this.options.getFileExtensions());
return new RequestMappingInfo(this.mappingName, patternsCondition,
new RequestMethodsRequestCondition(methods),
new ParamsRequestCondition(this.params),
new HeadersRequestCondition(this.headers),
new ConsumesRequestCondition(this.consumes, this.headers),
new ProducesRequestCondition(this.produces, this.headers, manager),
this.customCondition);
}到这里，我们不难看出RequestMappingInfo实际上是封装了请求路径到对应的处理的方法的映射。然后回到方法detectHandlerMethods中，接下来就是将处理请求的方法进行注册
protected void registerHandlerMethod(Object handler, Method method, T mapping) {
//这个mappingRegistry是一个MappingRegistry的实例
this.mappingRegistry.register(mapping, handler, method);
}public void register(T mapping, Object handler, Method method) {
this.readWriteLock.writeLock().lock();
try {
HandlerMethod handlerMethod = createHandlerMethod(handler, method);
assertUniqueMethodMapping(handlerMethod, mapping);
if (logger.isInfoEnabled()) {
logger.info("Mapped \"" + mapping + "\" onto " + handlerMethod);
}
//将映射与对应方法存起来
this.mappingLookup.put(mapping, handlerMethod);
//将请求路径与映射对象存起来
List<String> directUrls = getDirectUrls(mapping);
for (String url : directUrls) {
this.urlLookup.add(url, mapping);
}
String name = null;
//获取RequestMappingInfo的name,将name与method存起来
if (getNamingStrategy() != null) {
name = getNamingStrategy().getName(handlerMethod, mapping);
addMappingName(name, handlerMethod);
}
CorsConfiguration corsConfig = initCorsConfiguration(handler, method, mapping);
if (corsConfig != null) {
this.corsLookup.put(handlerMethod, corsConfig);
}
//将映射对象和映射注册对象存起来
this.registry.put(mapping, new MappingRegistration<T>(mapping, handlerMethod, directUrls, name));
}
finally {
this.readWriteLock.writeLock().unlock();
}
}这样，所有请求的路径到Controller中处理请求的方法的映射都被注册到了RequestMappingHandlerMapping中。下面我们就来具体看看SpringMVC中对请求的分发处理的过程。让我们重新回到DispatcherServlet中，前面说过，web请求的分发主要通过它来完成，作为一个Servlet，DispatcherServlet通过doService方法来相应http请求，下面我们来看看doService方法的实现
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));
}
}
}
// 将一些参数设置到request请求中
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 {
//具体分发的请求过程在这个方法中
doDispatch(request, response);
}
finally {
if (!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
// Restore the original attribute snapshot, in case of an include.
if (attributesSnapshot != null) {
restoreAttributesAfterInclude(request, attributesSnapshot);
}
}
}
}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);
// 根据请求获取HandlerExecutionChain,这个mappedHandler是一个HandlerExecutionChain对象,
//HandlerExecutionChain中设置了一个拦截器链,用来对handler进行增强,handler实际就是请求对应的Controller中的处理方法
mappedHandler = getHandler(processedRequest);
if (mappedHandler == null || mappedHandler.getHandler() == null) {
noHandlerFound(processedRequest, response);
return;
}
// 获取对应的HandlerAdapter,如果是配置了<mvc:annotation-driven/>,那么这里是RequestMappingHandlerAdapter
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;
}
}
//调用HandlerExecutionChain中的interceptor进行前置处理
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
// 调用HandlerAdapter的handler方法对handler进行处理并将处理的结果封装到ModelAndView中,为视图展现提供数据
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
//如果视图为空那么设置一个默认的视图
applyDefaultViewName(processedRequest, mv);
//调用HandlerExecutionChain中的interceptor进行后置处理
mappedHandler.applyPostHandle(processedRequest, response, mv);
}
catch (Exception ex) {
dispatchException = ex;
}
catch (Throwable err) {
// As of 4.3, we're processing Errors thrown from handler methods as well,
// making them available for @ExceptionHandler methods and other scenarios.
dispatchException = new NestedServletException("Handler dispatch failed", err);
}
//对ModelAndView视图的展现
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()) {
// 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);
}
}
}
}我们来看看getHandler中是如何获取HandlerExecutionChain的
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
//遍历handlerMappings,调用HandlerMapping的getHandler方法获取HandlerExecutionChain,
//在其中一个取到了立即返回
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;
}该方法的实现在AbstractHandlerMapping中，是一个final方法
public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
//获取对应的处理请求的方法
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);
}
//获取HandlerExecutionChain
HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);
if (CorsUtils.isCorsRequest(request)) {
CorsConfiguration globalConfig = this.corsConfigSource.getCorsConfiguration(request);
CorsConfiguration handlerConfig = getCorsConfiguration(handler, request);
CorsConfiguration config = (globalConfig != null ? globalConfig.combine(handlerConfig) : handlerConfig);
executionChain = getCorsHandlerExecutionChain(request, executionChain, config);
}
return executionChain;
}getHandlerInternal方法的实现在AbstractHandlerMethodMapping类中实现
protected HandlerMethod getHandlerInternal(HttpServletRequest request) throws Exception {
//获取请求的路径
String lookupPath = getUrlPathHelper().getLookupPathForRequest(request);
if (logger.isDebugEnabled()) {
logger.debug("Looking up handler method for path " + lookupPath);
}
this.mappingRegistry.acquireReadLock();
try {
//根据请求路径获取对应的处理请求的HandlerMethod
HandlerMethod handlerMethod = lookupHandlerMethod(lookupPath, request);
if (logger.isDebugEnabled()) {
if (handlerMethod != null) {
logger.debug("Returning handler method [" + handlerMethod + "]");
}
else {
logger.debug("Did not find handler method for [" + lookupPath + "]");
}
}
//将找到的HandlerMethod返回
return (handlerMethod != null ? handlerMethod.createWithResolvedBean() : null);
}
finally {
this.mappingRegistry.releaseReadLock();
}
}protected HandlerMethod lookupHandlerMethod(String lookupPath, HttpServletRequest request) throws Exception {
List<Match> matches = new ArrayList<Match>();
//这个directPathMatches实际上是一个RequestMappingInfo的集合,getMappingsByUrl方法会从之前
//RequestMappingHandlerMapping初始化时缓存到mappingRegistry中的urlLookup里取得对应的RequestMappingInfo
List<T> directPathMatches = this.mappingRegistry.getMappingsByUrl(lookupPath);
//从RequestMappingHandlerMapping初始化时缓存到mappingRegistry中的mappingLookup里获取对应的HandlerMethod,
//并和RequestMappingHandlerMapping、RequestMappingInfo一起封装到matches中
if (directPathMatches != null) {
addMatchingMappings(directPathMatches, matches, request);
}
if (matches.isEmpty()) {
// No choice but to go through all mappings...
addMatchingMappings(this.mappingRegistry.getMappings().keySet(), matches, request);
}
//返回一个最匹配的HandlerMethod
if (!matches.isEmpty()) {
Comparator<Match> comparator = new MatchComparator(getMappingComparator(request));
Collections.sort(matches, comparator);
if (logger.isTraceEnabled()) {
logger.trace("Found " + matches.size() + " matching mapping(s) for [" +
lookupPath + "] : " + matches);
}
Match bestMatch = matches.get(0);
if (matches.size() > 1) {
if (CorsUtils.isPreFlightRequest(request)) {
return PREFLIGHT_AMBIGUOUS_MATCH;
}
Match secondBestMatch = matches.get(1);
if (comparator.compare(bestMatch, secondBestMatch) == 0) {
Method m1 = bestMatch.handlerMethod.getMethod();
Method m2 = secondBestMatch.handlerMethod.getMethod();
throw new IllegalStateException("Ambiguous handler methods mapped for HTTP path '" +
request.getRequestURL() + "': {" + m1 + ", " + m2 + "}");
}
}
handleMatch(bestMatch.mapping, lookupPath, request);
return bestMatch.handlerMethod;
}
else {
return handleNoMatch(this.mappingRegistry.getMappings().keySet(), lookupPath, request);
}
}getHandlerExecutionChain的代码如下
protected HandlerExecutionChain getHandlerExecutionChain(Object handler, HttpServletRequest request) {
//创建一个HandlerExecutionChain
HandlerExecutionChain chain = (handler instanceof HandlerExecutionChain ?
(HandlerExecutionChain) handler : new HandlerExecutionChain(handler));
//获取请求的路径
String lookupPath = this.urlPathHelper.getLookupPathForRequest(request);
//遍历adaptedInterceptors,这个adaptedInterceptors是一个HandlerInterceptor的集合,集合中的interceptor是在初始化时添加进去的
for (HandlerInterceptor interceptor : this.adaptedInterceptors) {
if (interceptor instanceof MappedInterceptor) {
MappedInterceptor mappedInterceptor = (MappedInterceptor) interceptor;
//如果拦截器与路径匹配的话就将拦截器添加到HandlerExecutionChain的interceptorList中
if (mappedInterceptor.matches(lookupPath, this.pathMatcher)) {
chain.addInterceptor(mappedInterceptor.getInterceptor());
}
}
else {
chain.addInterceptor(interceptor);
}
}
return chain;
}这样就取到了所需要的HandlerExecutionChain，然后回到DispatcherServlet的doDispatch方法中，接下来我们看看这个方法中如何通过调用HandlerAdapter的handle方法获取到ModelAndView，以RequestMappingHandlerAdapter为例，如果配置了<mvc:annotation-driven/>，就会以这个类作为HandlerAdapter的实现，具体的获取ModelAndView的过程在handleInternal方法中
protected ModelAndView handleInternal(HttpServletRequest request,
HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
ModelAndView mav;
checkRequest(request);
// Execute invokeHandlerMethod in synchronized block if required.
if (this.synchronizeOnSession) {
HttpSession session = request.getSession(false);
if (session != null) {
Object mutex = WebUtils.getSessionMutex(session);
synchronized (mutex) {
mav = invokeHandlerMethod(request, response, handlerMethod);
}
}
else {
// No HttpSession available -> no mutex necessary
mav = invokeHandlerMethod(request, response, handlerMethod);
}
}
else {
//调用处理请求的handlerMethod,将方法中的参数及返回的视图封装到ModelAndView中
mav = invokeHandlerMethod(request, response, handlerMethod);
}
if (!response.containsHeader(HEADER_CACHE_CONTROL)) {
if (getSessionAttributesHandler(handlerMethod).hasSessionAttributes()) {
applyCacheSeconds(response, this.cacheSecondsForSessionAttributeHandlers);
}
else {
prepareResponse(response);
}
}
return mav;
}再回到doDispatcher中，然后会调用processDispatchResult方法对视图进行展现
private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
HandlerExecutionChain mappedHandler, ModelAndView mv, Exception exception) throws Exception {
boolean errorView = false;
if (exception != null) {
if (exception instanceof ModelAndViewDefiningException) {
logger.debug("ModelAndViewDefiningException encountered", exception);
mv = ((ModelAndViewDefiningException) exception).getModelAndView();
}
else {
Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
mv = processHandlerException(request, response, handler, exception);
errorView = (mv != null);
}
}
// 这里是展现视图的地方
if (mv != null && !mv.wasCleared()) {
render(mv, request, response);
if (errorView) {
WebUtils.clearErrorRequestAttributes(request);
}
}
else {
if (logger.isDebugEnabled()) {
logger.debug("Null ModelAndView returned to DispatcherServlet with name '" + getServletName() +
"': assuming HandlerAdapter completed request handling");
}
}
if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
// Concurrent handling started during a forward
return;
}
if (mappedHandler != null) {
mappedHandler.triggerAfterCompletion(request, response, null);
}
}具体的展现视图的方法在render方法中
protected void render(ModelAndView mv, HttpServletRequest request, HttpServletResponse response) throws Exception {
// 从request中获取locale信息并设置到response中
Locale locale = this.localeResolver.resolveLocale(request);
response.setLocale(locale);
View view;
if (mv.isReference()) {
// 从ModelAndView对象中获取视图名称并用ViewResolver解析得到视图对象
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 {
// 如果ModelAndView中已经包含视图对象那么直接取
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 {
if (mv.getStatus() != null) {
response.setStatus(mv.getStatus().value());
}
//调用视图对象的render方法展现视图
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;
}
}SpringMVC中封装了很多视图，比如JSP视图，FreeMarker视图，Velocity视图，Excel和PDF视图等等，我们来看看我们平常用的最多的JSP视图是如何展现的。具体的render方法的实现在AbstractView中
public 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);
}
//将model中的数据都收集到一个map中
Map<String, Object> mergedModel = createMergedOutputModel(model, request, response);
prepareResponse(request, response);
//展现模型数据到视图中
renderMergedOutputModel(mergedModel, getRequestToExpose(request), response);
}renderMergedOutputModel的实现在InternalResourceView中
protected void renderMergedOutputModel(
Map<String, Object> model, HttpServletRequest request, HttpServletResponse response) throws Exception {
// 将模型的数据设置到HTTPServletRequest中
exposeModelAsRequestAttributes(model, request);
// Expose helpers as request attributes, if any.
exposeHelpers(request);
// 获取视图页面的内部资源路径
String dispatcherPath = prepareForRendering(request, response);
// 获取RequestDispatcher
RequestDispatcher rd = getRequestDispatcher(request, 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(request, response)) {
response.setContentType(getContentType());
if (logger.isDebugEnabled()) {
logger.debug("Including resource [" + getUrl() + "] in InternalResourceView '" + getBeanName() + "'");
}
rd.include(request, response);
}
else {
// 将请求到资源上,比如JSP页面,JSP页面的展现由web容器负责,view只是转发请求
if (logger.isDebugEnabled()) {
logger.debug("Forwarding to resource [" + getUrl() + "] in InternalResourceView '" + getBeanName() + "'");
}
rd.forward(request, response);
}
}至此，SpringMVC就完成了将HTTP请求通过DispatcherServlet转发给页面呈现的过程。总结一下，SpringMVC的实现由以下三个步骤完成：
1、初始化handlerMapping时，http请求到Controller之间的映射会被载入到HandlerMapping中
2、当接收到http请求之后，DispatcherServlet会根据具体的URL信息，在HandlerMapping中查询，然后得到对应的HandlerExecutionChain。HandlerExecutionChain中封装了对应的处理请求的HandlerMethod，然后HandlerAdapter会执行处理请求的方法，生成需要的ModelAndView对象。
3、得到ModelAndView对象之后，DispatcherServlet把获取的模型数据交给特定的视图对象，从而完成这些数据的呈现工作，呈现的过程由对应的视图类的render方法完成。
本文章为转载内容，我们尊重原作者对文章享有的著作权。如有内容错误或侵权问题，欢迎原作者联系我们进行内容更正或删除文章。
