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SpringMVC源码分析之策略对象初始化

前面我们分析了springmvc的各种组件,那么组件在什么时候初始化的呢?我们这里就研究一下。

【1】DispatcherServlet

① 核心属性

DispatcherServlet有许多属性,除了一些 static final类型的常量,其他类似如​​List<HandlerMapping> handlerMappings​​是在实例化过程中赋值的。

// 如下是一些静态常量,默认类加载时已赋值
public static final String MULTIPART_RESOLVER_BEAN_NAME = "multipartResolver";
public static final String LOCALE_RESOLVER_BEAN_NAME = "localeResolver";
public static final String THEME_RESOLVER_BEAN_NAME = "themeResolver";
public static final String HANDLER_MAPPING_BEAN_NAME = "handlerMapping";
public static final String HANDLER_ADAPTER_BEAN_NAME = "handlerAdapter";
public static final String HANDLER_EXCEPTION_RESOLVER_BEAN_NAME = "handlerExceptionResolver";
public static final String REQUEST_TO_VIEW_NAME_TRANSLATOR_BEAN_NAME = "viewNameTranslator";
public static final String VIEW_RESOLVER_BEAN_NAME = "viewResolver";
public static final String FLASH_MAP_MANAGER_BEAN_NAME = "flashMapManager";
// 下面是请求属性部分key
public static final String WEB_APPLICATION_CONTEXT_ATTRIBUTE = DispatcherServlet.class.getName() + ".CONTEXT";
public static final String LOCALE_RESOLVER_ATTRIBUTE = DispatcherServlet.class.getName() + ".LOCALE_RESOLVER";
public static final String THEME_RESOLVER_ATTRIBUTE = DispatcherServlet.class.getName() + ".THEME_RESOLVER";
public static final String THEME_SOURCE_ATTRIBUTE = DispatcherServlet.class.getName() + ".THEME_SOURCE";
public static final String INPUT_FLASH_MAP_ATTRIBUTE = DispatcherServlet.class.getName() + ".INPUT_FLASH_MAP";
public static final String OUTPUT_FLASH_MAP_ATTRIBUTE = DispatcherServlet.class.getName() + ".OUTPUT_FLASH_MAP";
public static final String FLASH_MAP_MANAGER_ATTRIBUTE = DispatcherServlet.class.getName() + ".FLASH_MAP_MANAGER";
public static final String EXCEPTION_ATTRIBUTE = DispatcherServlet.class.getName() + ".EXCEPTION";
public static final String PAGE_NOT_FOUND_LOG_CATEGORY = "org.springframework.web.servlet.PageNotFound";
// DispatcherServlet.properties 里面可以配置了一些策略接口的默认值,
//比如 HandlerMapping=RequestMappingHandlerMapping
private static final String DEFAULT_STRATEGIES_PATH = "DispatcherServlet.properties";
private static final String DEFAULT_STRATEGIES_PREFIX = "org.springframework.web.servlet";
protected static final Log pageNotFoundLogger = LogFactory.getLog(PAGE_NOT_FOUND_LOG_CATEGORY);

/** Store default strategy implementations. */
@Nullable
private static Properties defaultStrategies;
// 下面这些属性在实例化调用构造函数时会被重新赋值
/** 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;

/** Throw a NoHandlerFoundException if no Handler was found to process this request? *.*/
private boolean throwExceptionIfNoHandlerFound = false;

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

// 下面这些属性将在initStrategies方法中被调用
/** MultipartResolver used by this servlet. */
@Nullable
private MultipartResolver multipartResolver;

/** LocaleResolver used by this servlet. */
@Nullable
private LocaleResolver localeResolver;

/** ThemeResolver used by this servlet. */
@Nullable
private ThemeResolver themeResolver;

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

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

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

/** RequestToViewNameTranslator used by this servlet. */
@Nullable
private RequestToViewNameTranslator viewNameTranslator;

/** FlashMapManager used by this servlet. */
@Nullable
private FlashMapManager flashMapManager;

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

private boolean parseRequestPath;

我们下面要分析的就是诸如viewResolvers、handlerExceptionResolvers等在何时被实例化并注入。

② 继承树

如下所示是​​DispatcherServlet​​​的继承树示意图,其继承自​​FrameworkServlet​​​,而​​FrameworkServlet​​​又继承了​​HttpServletBean​​​并实现了​​ApplicationContextAware​​接口。

​HttpServletBean​​​ 则继承了HttpServlet 并实现 EnvironmentCapable, EnvironmentAware接口。所以本质上DispatcherServlet是一个httpservlet,当实例化bean时会调用其init方法。
SpringMVC源码分析之策略对象初始化_spring
我们就从其init方法入手分析。

首先会调用DispatcherServlet的无参构造方法,这里会为其成品变量赋值。

public DispatcherServlet() {
super();
setDispatchOptionsRequest(true);
}

然后会调用其父类​​GenericServlet​​的​​init(ServletConfig config)​​方法,其子类​​HttpServletBean​​​重写了父类​​GenericServlet​​​的​​void init()​​​方法,方法如下所示主要是获取初始化参数为servlet 成员赋值,然后调用​​initServletBean​​方法。但是这是一个空方法,留给子类FrameworkServlet实现。

  • web容器在实例化servlet时会调用Servlet的​​init(ServletConfig)​​​方法,由于其子类GenericServlet实现了该方法,因而最终会调用​​GenericServlet.init(ServletConfig)​​方法。
  • ​GenericServlet.init(ServletConfig)​​​方法内部会调用其init()方法,由于该方法又是由其子类HttpServletBean实现,实际上是执行了​​HttpServletBean.init()​​方法。
  • ​HttpServletBean.init()​​​方法内部会调用其自定义的​​initServletBean()​​​方法,但该方法实际上是由FrameworkServlet实现,实际上是执行了​​FrameworkServlet.initServletBean()​​方法。
  • ​FrameworkServlet.initServletBean()​​​方法内部真正初始化了applicationContext,并加载配置文件,最终调用其自定义的​​initFrameworkServlet()​​方法。
@Override
public final void init() throws ServletException {

// Set bean properties from init parameters.
PropertyValues pvs = new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);
if (!pvs.isEmpty()) {
try {
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) {
if (logger.isErrorEnabled()) {
logger.error("Failed to set bean properties on servlet '" + getServletName() + "'", ex);
}
throw ex;
}
}

// Let subclasses do whatever initialization they like.
initServletBean();
}

我们继续看下FrameworkServlet的initServletBean方法。

核心代码只有两句,在servlet 属性被赋值后调用,初始化servlet容器也就是springmvc的容器(本文这里不是springboot环境,关于springboot环境下容器参考博文Spring、SpringMVC和SpringBoot框架中那些容器)。

​initFrameworkServlet​​​是个空方法,没有实现,这里核心就是​​initWebApplicationContext​​方法。

@Override
protected final void initServletBean() throws ServletException {
// 比如Initializing Spring DispatcherServlet 'DispatcherServlet'
getServletContext().log("Initializing Spring " + getClass().getSimpleName() + " '" + getServletName() + "'");
if (logger.isInfoEnabled()) {
logger.info("Initializing Servlet '" + getServletName() + "'");
}
long startTime = System.currentTimeMillis();

try {
this.webApplicationContext = initWebApplicationContext();
initFrameworkServlet();
}
//...
}

③ 内部类ContextRefreshListener

如下所示其实现了ApplicationListener接口,对ContextRefreshedEvent事件感兴趣。也就是说如果应用广播了ContextRefreshedEvent事件,那么其方法​​FrameworkServlet.this.onApplicationEvent(event);​​将会被调用。

private class ContextRefreshListener implements ApplicationListener<ContextRefreshedEvent> {

@Override
public void onApplicationEvent(ContextRefreshedEvent event) {
FrameworkServlet.this.onApplicationEvent(event);
}
}

那么流程就很清晰了,当ContextRefreshedEvent事件被广播出来时就会调用这里onApplicationEvent方法,继而触发​​onRefresh(event.getApplicationContext());​​​–​​initStrategies(context);​​进行基础策略对象的实例化。

public void onApplicationEvent(ContextRefreshedEvent event) {
this.refreshEventReceived = true;
synchronized (this.onRefreshMonitor) {
onRefresh(event.getApplicationContext());
}
}

@Override
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);
}

ContextRefreshedEvent 事件是上下文刷新事件,该事件是在容器初始化过程中被广播出来的,下面我们分析这个容器初始化过程。

【2】容器初始化

① initWebApplicationContext

​initWebApplicationContext​​​将会初始化容器并将容器发布到servletContext中,作为其一个属性。这里首先会尝试获取​​rootContext​​ (SSM环境下指的是spring容器),作为springMVC容器的parent。

该方法不会创建springMVC容器,而是委派给​​createWebApplicationContext​​创建。

protected WebApplicationContext initWebApplicationContext() {
// 获取rootContext将会作为springmvc容器的parent
WebApplicationContext rootContext =
WebApplicationContextUtils.getWebApplicationContext(getServletContext());
WebApplicationContext wac = null;

// 如果构造函数注入了webApplicationContext ,那么将会作为springMVC容器
if (this.webApplicationContext != null) {
// A context instance was injected at construction time -> use it
wac = this.webApplicationContext;
// 如果是ConfigurableWebApplicationContext类型,且容器未激活,
//则尝试设置父类然后配置、刷新容器
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);
}
}
}
// 尝试从servlet context寻找容器,
//如果找到就认为该容器已经设置了parent并配置、刷新过
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();
}
// 实际创建容器的方法
if (wac == null) {
// No context instance is defined for this servlet -> create a local one
wac = createWebApplicationContext(rootContext);
}
// 如果refreshEventReceived为false,也就是没有刷新过,那么手动调用onRefresh进行刷新
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.
synchronized (this.onRefreshMonitor) {
onRefresh(wac);
}
}
// 作为servletContext属性将自身放入
if (this.publishContext) {
// Publish the context as a servlet context attribute.
//org.springframework.web.servlet.FrameworkServlet.CONTEXT.DispatcherServlet
// DispatcherServlet 是本文这里配置的servlet nam
String attrName = getServletContextAttributeName();
getServletContext().setAttribute(attrName, wac);
}

return wac;
}

代码解释如下:

  • ① 根据属性​​ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE(WebApplicationContext.class.getName() + ".ROOT")​​尝试获取rootContext,其将作为springMVC容器的parent;
  • ② 如果当前对象的​​webApplicationContext​​​不为null,也就是说实例化时通过有参构造函数注入了​​webApplicationContext​​,那么其将作为springMVC容器;
  • ③ 如果容器是​​ConfigurableWebApplicationContext​​​类型,其未激活,那么尝试设置parent,并调用​​configureAndRefreshWebApplicationContext​​进行配置、刷新。
  • ④ 如果容器未null,那么尝试根据其成员变量​​contextAttribute​​​的值作为属性从ServletContext中获取;默认​​contextAttribute​​为null。
  • ⑤ 如果wac为null,也就是springmvc此时仍旧为null,那么调用​​createWebApplicationContext​​方法进行创建;
  • ⑥ 如果没有执行过刷新,也就是​​refreshEventReceived​​​为false,那么这里加锁调用onRefresh方法。在起​​onApplicationEvent​​方法中,该属性将会变为true。
  • ⑦ 如果​​publishContext​​​为true,那么将当前容器发布到ServletContext中作为其属性。属性key为:​​FrameworkServlet.class.getName() + ".CONTEXT."+serveletName​

这里的核心方法是:​​createWebApplicationContext​​​和​​configureAndRefreshWebApplicationContext​​。前者进行创建,后置进行配置、刷新、发布事件等等操作。

② createWebApplicationContext

我们继续看下FrameworkServlet的createWebApplicationContext方法。

protected WebApplicationContext createWebApplicationContext(@Nullable ApplicationContext parent) {
// 获取class,本文这里默认是XmlWebApplicationContext
Class<?> contextClass = getContextClass();
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");
}
// 实例化
ConfigurableWebApplicationContext wac =
(ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
// 设置environment
wac.setEnvironment(getEnvironment());
// 设置parent
wac.setParent(parent);
// 设置配置文件路径
String configLocation = getContextConfigLocation();
if (configLocation != null) {
wac.setConfigLocation(configLocation);
}
// 关键核心步骤
configureAndRefreshWebApplicationContext(wac);

return wac;
}

代码逻辑很清晰,获取contextClass,然后进行实例化、设置environment、parent、configLocation等,最后调用​​configureAndRefreshWebApplicationContext​​对容器进行配置并刷新。

分析到这里,还没有看到诸如viewResolvers、handlerExceptionResolvers等被实例化的影子,那么肯定就在​​configureAndRefreshWebApplicationContext​​方法里面了。

③ configureAndRefreshWebApplicationContext

这里配置的​​servlet-name​​​是​​DispatcherServlet​​。

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());
}
}
// 设置web 上下文--这是Tomcat的哦
wac.setServletContext(getServletContext());
// 设置上下文配置
wac.setServletConfig(getServletConfig());
// 设置namespace 比如getServletName() + DEFAULT_NAMESPACE_SUFFIX
wac.setNamespace(getNamespace());
// 添加上下文刷新监听器,ContextRefreshListener对ContextRefreshedEvent事件感兴趣
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) {
// 设置ServletContextPropertySource ServletConfigPropertySource
((ConfigurableWebEnvironment) env).initPropertySources(getServletContext(), getServletConfig());
}
// 容器的后置处理
postProcessWebApplicationContext(wac);
// 将容器交给ApplicationContextInitializer
applyInitializers(wac);
// 刷新容器
wac.refresh();
}

方法逻辑解释如下:

  • ① 设置id,如​​org.springframework.web.context.WebApplicationContext:/DispatcherServlet;​
  • ② 设置servletContext引用,这是属于web server的根容器,这里是Tomcat的容器;
  • ③ 设置servletConfig
  • ④ 设置namespace 比如​​getServletName() + DEFAULT_NAMESPACE_SUFFIX​
  • ⑤ 添加上下文刷新监听器,​​ContextRefreshListener​​​对​​ContextRefreshedEvent​​事件感兴趣;
  • ⑥ 获取​​ConfigurableEnvironment​​​ ,并设置​​ServletContextPropertySource​​​ 、​​ServletConfigPropertySource​
  • ⑦​​postProcessWebApplicationContext​​​对容器进行后置处理,该方法默认为空,没有实现。容器的修操作交给​​ApplicationContextInitializer​​。
  • ⑧​​applyInitializers​​​将容器交给一系列​​ApplicationContextInitializer​​初始化器
  • ⑨ wac.refresh()刷新容器

④ refresh刷新容器

AbstractApplicationContext的refresh是个典型的模板方法,由众多核心方法组成。

@Override
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
StartupStep contextRefresh = this.applicationStartup.start("spring.context.refresh");

// Prepare this context for refreshing.
prepareRefresh();

// Tell the subclass to refresh the internal bean factory.
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

// Prepare the bean factory for use in this context.
prepareBeanFactory(beanFactory);

try {
// Allows post-processing of the bean factory in context subclasses.
postProcessBeanFactory(beanFactory);

StartupStep beanPostProcess = this.applicationStartup.start("spring.context.beans.post-process");
// Invoke factory processors registered as beans in the context.
invokeBeanFactoryPostProcessors(beanFactory);

// Register bean processors that intercept bean creation.
registerBeanPostProcessors(beanFactory);
beanPostProcess.end();

// Initialize message source for this context.
initMessageSource();

// Initialize event multicaster for this context.
initApplicationEventMulticaster();

// Initialize other special beans in specific context subclasses.
onRefresh();

// Check for listener beans and register them.
registerListeners();

// Instantiate all remaining (non-lazy-init) singletons.
finishBeanFactoryInitialization(beanFactory);

// Last step: publish corresponding event.
finishRefresh();
}

catch (BeansException ex) {
if (logger.isWarnEnabled()) {
logger.warn("Exception encountered during context initialization - " +
"cancelling refresh attempt: " + ex);
}

// Destroy already created singletons to avoid dangling resources.
destroyBeans();

// Reset 'active' flag.
cancelRefresh(ex);

// Propagate exception to caller.
throw ex;
}

finally {
// Reset common introspection caches in Spring's core, since we
// might not ever need metadata for singleton beans anymore...
resetCommonCaches();
contextRefresh.end();
}
}
}

本文这里我们不关心每一个方法,我们只看​​initApplicationEventMulticaster​​(初始化广播器)、registerListeners();(注册监听器)以及finishRefresh(发布事件)。其他方法我们留在分析spring容器初始化过程时展开。

在前面Spring中事件监听(通知)机制详解与实践一文中我们详细分析了事件广播机制与监听器、广播器的注册。这里我们不再赘述直接看finishRefresh();方法。

如下所示在​​publishEvent(new ContextRefreshedEvent(this));​​​会广播事件​​ContextRefreshedEvent​​​给所有的监听器。那么​​FrameworkServlet​​​的内部类​​ContextRefreshListener​​​的​​onApplicationEvent​​方法将会被触发。

protected void finishRefresh() {
// Clear context-level resource caches (such as ASM metadata from scanning).
clearResourceCaches();

// Initialize lifecycle processor for this context.
initLifecycleProcessor();

// Propagate refresh to lifecycle processor first.
getLifecycleProcessor().onRefresh();

// Publish the final event.
publishEvent(new ContextRefreshedEvent(this));

// Participate in LiveBeansView MBean, if active.
if (!IN_NATIVE_IMAGE) {
LiveBeansView.registerApplicationContext(this);
}
}

【3】策略对象初始化

当事件​​ContextRefreshedEvent​​被广播出来时,最终会触发下面initStrategies方法进行策略对象的初始化。

protected void initStrategies(ApplicationContext context) {
initMultipartResolver(context);
initLocaleResolver(context);
initThemeResolver(context);
initHandlerMappings(context);
initHandlerAdapters(context);
initHandlerExceptionResolvers(context);
initRequestToViewNameTranslator(context);
initViewResolvers(context);
initFlashMapManager(context);
}

方法解释如下所示:

  • ① 初始化MultipartResolver,主要用来处理文件上传;
  • ② 初始化区域解析器,主要用来解析区域信息应用于国际化场景;
  • ③ 初始化主题解析器,默认是FixedThemeResolver;
  • ④ 初始化处理器映射器,这个很关键哦;
  • ⑤ 初始化处理器适配器,这个很关键哦;
  • ⑥ 初始化异常解析器,这个很关键哦;
  • ⑦ 初始化请求视图名称转换器,默认是DefalutRequestToViewNameTranslator;
  • ⑧ 初始化视图解析器;
  • ⑨ 初始化闪存属性管理器。

关于闪存属性管理器可以参考SpringMVC中重定向请求时传输参数原理分析与实践

关于处理器适配器可以参考:SpringMVC常见组件之HandlerAdapter分析

关于处理器映射器可以参考:SpringMVC常见组件之HandlerMapping分析

关于参数解析器可以参考:SpringMVC常见组件之HandlerMethodArgumentResolver解析

关于返回结果处理器可以参考:SpringMVC常见组件HandlerMethodReturnValueHandler解析

关于数据绑定与格式化转换可以参考:SpringMVC常见组件之DataBinder数据绑定器分析

关于视图解析器可以参考:SpringMVC常见组件之ViewResolver分析

关于异常解析器可以参考:SpringMVC常见组件之HandlerExceptionResolver分析

下面我们见到看下这九个方法。

① initMultipartResolver

这里​​MULTIPART_RESOLVER_BEAN_NAME=multipartResolver​​​,默认将会获取得到一个CommonsMultipartResolver实例。如果实例化失败,将会抛出​​NoSuchBeanDefinitionException​​异常。

private void initMultipartResolver(ApplicationContext context) {
try {
this.multipartResolver = context.getBean(MULTIPART_RESOLVER_BEAN_NAME, MultipartResolver.class);
//...
}
}

SpringMVC源码分析之策略对象初始化_初始化_02

② initLocaleResolver

这里​​LOCALE_RESOLVER_BEAN_NAME=localeResolver​​​,默认将会获取得到一个AcceptHeaderLocaleResolver实例。如果实例化失败,将会抛出​​NoSuchBeanDefinitionException​​异常。

private void initLocaleResolver(ApplicationContext context) {
try {
this.localeResolver = context.getBean(LOCALE_RESOLVER_BEAN_NAME, LocaleResolver.class);
//...
}
}

③ initThemeResolver

这里​​THEME_RESOLVER_BEAN_NAME=themeResolver​​​,默认将会获取得到一个FixedThemeResolver实例。如果实例化失败,将会抛出​​NoSuchBeanDefinitionException​​异常。

private void initThemeResolver(ApplicationContext context) {
try {
this.themeResolver = context.getBean(THEME_RESOLVER_BEAN_NAME, ThemeResolver.class);
//...
}
}

④ initHandlerMappings

private void initHandlerMappings(ApplicationContext context) {
this.handlerMappings = null;
// 是否检测所有handlermappings? 默认true
if (this.detectAllHandlerMappings) {
// 从容器中获取所有的HandlerMapping,如viewControllerHandlerMapping
Map<String, HandlerMapping> matchingBeans =
BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false);
if (!matchingBeans.isEmpty()) {
this.handlerMappings = new ArrayList<>(matchingBeans.values());
// 对handlerMappings 按照order值 进行排序
AnnotationAwareOrderComparator.sort(this.handlerMappings);
}
}
else {
try {
// 获取一个bean name为handlerMapping的实例
// HANDLER_MAPPING_BEAN_NAME = "handlerMapping"
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handlerMappings 仍旧为null,则从默认策略配置中获取
if (this.handlerMappings == null) {
// 尝试从DispatcherServlet.properties获取HandlerMapping对应的value,进行实例化
this.handlerMappings = getDefaultStrategies(context, HandlerMapping.class);
if (logger.isTraceEnabled()) {
logger.trace("No HandlerMappings declared for servlet '" + getServletName() +
"': using default strategies from DispatcherServlet.properties");
}
}
// 遍历处理HandlerMapping
for (HandlerMapping mapping : this.handlerMappings) {
// 判断当前handlermapping的patternParser是否为null
if (mapping.usesPathPatterns()) {
this.parseRequestPath = true;
break;
}
}
}

Spring 5带来 PathPatternParser,用于解析URI模板模式。PathPatternParser将路径分成PathElements的链接列表。这一链条PathElements采取的是PathPattern的模式快速匹配的类。

​AnnotationAwareOrderComparator.sort(this.handlerMappings);​​​表示根据​​handlermapping​​​的order属性值进行排序。排序前:
SpringMVC源码分析之策略对象初始化_初始化_03
其中beanName为​​​viewControllerHandlerMapping​​​对应的实际bean是​​SimpleUrlHandlerMapping​​​,通常由​​ <mvc:view-controller path="/" view-name="index"></mvc:view-controller>​​​配置生成。
SpringMVC源码分析之策略对象初始化_初始化_04

排序后:
SpringMVC源码分析之策略对象初始化_初始化_05
最后一个​​​SimpleUrlHandlerMapping​​​则是默认拦截所有然后交给springmvc的默认处理器。
SpringMVC源码分析之策略对象初始化_mvc_06

⑤ initHandlerAdapters

​initHandlerAdaptersd​​​的过程与​​initHandlerMappings​​过程一致:

  • ① 检测容器中所有的HandlerAdapter,得到实例并排序;
  • ② 如果①没有得到,则尝试获取一个beanName为handlerAdapter的实例;
  • ③ 如果②仍旧没有得到,则使用默认策略获取HandlerAdapter
private void initHandlerAdapters(ApplicationContext context) {
this.handlerAdapters = null;

if (this.detectAllHandlerAdapters) {
// Find all HandlerAdapters in the ApplicationContext, including ancestor contexts.
Map<String, HandlerAdapter> matchingBeans =
BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerAdapter.class, true, false);
if (!matchingBeans.isEmpty()) {
this.handlerAdapters = new ArrayList<>(matchingBeans.values());
// We keep HandlerAdapters in sorted order.
AnnotationAwareOrderComparator.sort(this.handlerAdapters);
}
}
else {
try {
HandlerAdapter ha = context.getBean(HANDLER_ADAPTER_BEAN_NAME, HandlerAdapter.class);
this.handlerAdapters = Collections.singletonList(ha);
}
catch (NoSuchBeanDefinitionException ex) {
// Ignore, we'll add a default HandlerAdapter later.
}
}

// 使用默认策略获取handlerAdapters
if (this.handlerAdapters == null) {
this.handlerAdapters = getDefaultStrategies(context, HandlerAdapter.class);
if (logger.isTraceEnabled()) {
logger.trace("No HandlerAdapters declared for servlet '" + getServletName() +
"': using default strategies from DispatcherServlet.properties");
}
}
}

如下所示是得到的​​HandlerAdapter​​​(排序后的):
SpringMVC源码分析之策略对象初始化_初始化_07

⑥ initHandlerExceptionResolvers

​initHandlerExceptionResolvers​​​的过程与​​initHandlerMappings​​过程一致:

  • ① 检测容器中所有的HandlerExceptionResolver,得到实例并排序;
  • ② 如果①没有得到,则尝试获取一个beanName为handlerExceptionResolver的实例;
  • ③ 如果②仍旧没有得到,则使用默认策略获取handlerExceptionResolvers
private void initHandlerExceptionResolvers(ApplicationContext context) {
this.handlerExceptionResolvers = null;

if (this.detectAllHandlerExceptionResolvers) {
// Find all HandlerExceptionResolvers in the ApplicationContext, including ancestor contexts.
Map<String, HandlerExceptionResolver> matchingBeans = BeanFactoryUtils
.beansOfTypeIncludingAncestors(context, HandlerExceptionResolver.class, true, false);
if (!matchingBeans.isEmpty()) {
this.handlerExceptionResolvers = new ArrayList<>(matchingBeans.values());
// We keep HandlerExceptionResolvers in sorted order.
AnnotationAwareOrderComparator.sort(this.handlerExceptionResolvers);
}
}
else {
try {
HandlerExceptionResolver her =
context.getBean(HANDLER_EXCEPTION_RESOLVER_BEAN_NAME, HandlerExceptionResolver.class);
this.handlerExceptionResolvers = Collections.singletonList(her);
}
catch (NoSuchBeanDefinitionException ex) {
// Ignore, no HandlerExceptionResolver is fine too.
}
}

// Ensure we have at least some HandlerExceptionResolvers, by registering
// default HandlerExceptionResolvers if no other resolvers are found.
if (this.handlerExceptionResolvers == null) {
this.handlerExceptionResolvers = getDefaultStrategies(context, HandlerExceptionResolver.class);
if (logger.isTraceEnabled()) {
logger.trace("No HandlerExceptionResolvers declared in servlet '" + getServletName() +
"': using default strategies from DispatcherServlet.properties");
}
}
}

⑦ initRequestToViewNameTranslator

如下所示,从容器中获取一个​​beanName​​​为​​viewNameTranslator​​​的实例。这里得到的是​​DefaultRequestToViewNameTranslator​​。

private void initRequestToViewNameTranslator(ApplicationContext context) {
try {
this.viewNameTranslator =
context.getBean(REQUEST_TO_VIEW_NAME_TRANSLATOR_BEAN_NAME, RequestToViewNameTranslator.class);
//...
}
}

SpringMVC源码分析之策略对象初始化_mvc_08

⑧ initViewResolvers

​initViewResolvers​​​的过程与​​initHandlerMappings​​过程一致:

  • ① 检测容器中所有的s,得到实例并排序;
  • ② 如果①没有得到,则尝试获取一个beanName为viewResolver的实例;
  • ③ 如果②仍旧没有得到,则使用默认策略获取viewResolvers
private void initViewResolvers(ApplicationContext context) {
this.viewResolvers = null;

if (this.detectAllViewResolvers) {
// Find all ViewResolvers in the ApplicationContext, including ancestor contexts.
Map<String, ViewResolver> matchingBeans =
BeanFactoryUtils.beansOfTypeIncludingAncestors(context, ViewResolver.class, true, false);
if (!matchingBeans.isEmpty()) {
this.viewResolvers = new ArrayList<>(matchingBeans.values());
// We keep ViewResolvers in sorted order.
AnnotationAwareOrderComparator.sort(this.viewResolvers);
}
}
else {
try {
ViewResolver vr = context.getBean(VIEW_RESOLVER_BEAN_NAME, ViewResolver.class);
this.viewResolvers = Collections.singletonList(vr);
}
catch (NoSuchBeanDefinitionException ex) {
// Ignore, we'll add a default ViewResolver later.
}
}

// Ensure we have at least one ViewResolver, by registering
// a default ViewResolver if no other resolvers are found.
if (this.viewResolvers == null) {
this.viewResolvers = getDefaultStrategies(context, ViewResolver.class);
if (logger.isTraceEnabled()) {
logger.trace("No ViewResolvers declared for servlet '" + getServletName() +
"': using default strategies from DispatcherServlet.properties");
}
}
}

⑨ initFlashMapManager

如下所示,从容器中获取一个beanName为flashMapManagerd的实例。这里默认得到一个​​SessionFlashMapManager​​。SessionFlashMapManager提供了在session中检索和更新flashMap的方法。

private void initFlashMapManager(ApplicationContext context) {
try {
this.flashMapManager = context.getBean(FLASH_MAP_MANAGER_BEAN_NAME, FlashMapManager.class);
//...
}
}

SpringMVC源码分析之策略对象初始化_springmvc初始化_09

⑩ getDefaultStrategies

在spring-webmvc包中默认配置了​​DispatcherServlet.properties​​,用以在获取不到策略接口的情况下,实例化一个默认值。

//路径
org\springframework\spring-webmvc\5.3.1\spring-webmvc-5.3.1.jar!\org\springframework\web\servlet\DispatcherServlet.properties

# 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.method.annotation.RequestMappingHandlerMapping,\
org.springframework.web.servlet.function.support.RouterFunctionMapping

org.springframework.web.servlet.HandlerAdapter=org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter,\
org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter,\
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter,\
org.springframework.web.servlet.function.support.HandlerFunctionAdapter


org.springframework.web.servlet.HandlerExceptionResolver=org.springframework.web.servlet.mvc.method.annotation.ExceptionHandlerExceptionResolver,\
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

springmvc会根据入参中的​​Class<T> strategyInterface​​名称作为key获取对应的value,然后遍历实例化并放到List返回。

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

String key = strategyInterface.getName();
String value = defaultStrategies.getProperty(key);
if (value != null) {
String[] classNames = StringUtils.commaDelimitedListToStringArray(value);
List<T> strategies = new ArrayList<>(classNames.length);
for (String className : classNames) {
try {
Class<?> clazz = ClassUtils.forName(className, DispatcherServlet.class.getClassLoader());
Object strategy = createDefaultStrategy(context, clazz);
strategies.add((T) strategy);
}
catch (ClassNotFoundException ex) {
throw new BeanInitializationException(
"Could not find DispatcherServlet's default strategy class [" + className +
"] for interface [" + key + "]", ex);
}
catch (LinkageError err) {
throw new BeanInitializationException(
"Unresolvable class definition for DispatcherServlet's default strategy class [" +
className + "] for interface [" + key + "]", err);
}
}
return strategies;
}
else {
return Collections.emptyList();
}
}


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