SpringMVC 基本流程源码分析1_frameworkservlet 'springmvc': initialization compl-优快云博客

本文链接：https://blog.youkuaiyun.com/huang__2/article/details/105776923

SpringMVC 基本流程源码分析

`ContextLoaderListener`分析

 <!-- Spring监听器 -->
<listener>
 <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>

@Override
	public void contextInitialized(ServletContextEvent event) {
		// 初始化webApplicationContext
		initWebApplicationContext(event.getServletContext());
	}

public WebApplicationContext initWebApplicationContext(ServletContext servletContext) {
		if (servletContext.getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE) != null) {
			// web.xml 中存在多次ContextLoader定义
			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) {
				// 初始化context
				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.
						ApplicationContext parent = loadParentContext(servletContext);
						cwac.setParent(parent);
					}
					// 容器核心启动
					configureAndRefreshWebApplicationContext(cwac, servletContext);
				}
			}
			// 记录在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;
		}
	}

protected WebApplicationContext createWebApplicationContext(ServletContext sc) {
		Class<?> contextClass = determineContextClass(sc);
		// contextClass 不是ConfigurableWebApplicationContext 类型。
		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 Class<?> determineContextClass(ServletContext servletContext) {
		//CONTEXT_CLASS_PARAM = "contextClass";
		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 {
			// defaultStrategies 配置文件在哪加载。 通过静态代码块加载
			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);
			}
		}
	}

static {
		// Load default strategy implementations from properties file.
		// This is currently strictly internal and not meant to be customized
		// by application developers.
		try {
			// ContextLoader.properties 加载这个文件
			// org.springframework.web.context.WebApplicationContext
			// =org.springframework.web.context.support.XmlWebApplicationContext
			ClassPathResource resource = new ClassPathResource(DEFAULT_STRATEGIES_PATH, ContextLoader.class);
			//实例化defaultStrategies 属性
			defaultStrategies = PropertiesLoaderUtils.loadProperties(resource);
		}
		catch (IOException ex) {
			throw new IllegalStateException("Could not load 'ContextLoader.properties': " + ex.getMessage());
		}
	}

流程分析：

WebApplicationContext存在性验证。
创建WebApplicationContext 实例
- servletContext.getInitParameter(CONTEXT_CLASS_PARAM); 取得类
- defaultStrategies.getProperty(WebApplicationContext.class.getName());
  - defaultStrategies静态块实例化
将实例记录在servletContext
映射当前的类加载器与创建的实例到全局变量currentContextPerThread–>(Map)

DispatcherServlet 分析

DispatcherServlet 初始化

org.springframework.web.servlet.HttpServletBean#init父类初始化

@Override
	public final void init() throws ServletException {
		if (logger.isDebugEnabled()) {
			logger.debug("Initializing servlet '" + getServletName() + "'");
		}

		// Set bean properties from init parameters.
		// 解析init-param 并封装值PropertyValues中
		PropertyValues pvs = new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);
		if (!pvs.isEmpty()) {
			try {
				// 将当前的servlet 转化成一个BeanWrapper 能够以spring的方式来对init-param 的值进行注入
				BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
				ResourceLoader resourceLoader = new ServletContextResourceLoader(getServletContext());
				// 注册自定义属性编辑器，一旦遇到Resource类型的属性将ResourceEditor进行解析
				bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, getEnvironment()));
				// 空实现留个子类覆盖。
				initBeanWrapper(bw);
				// 属性注入
				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();

		if (logger.isDebugEnabled()) {
			logger.debug("Servlet '" + getServletName() + "' configured successfully");
		}
	}

public ServletConfigPropertyValues(ServletConfig config, Set<String> requiredProperties)
				throws ServletException {

			Set<String> missingProps = (!CollectionUtils.isEmpty(requiredProperties) ?
					new HashSet<>(requiredProperties) : null);

			Enumeration<String> paramNames = config.getInitParameterNames();
			while (paramNames.hasMoreElements()) {
				String property = paramNames.nextElement();
				Object value = config.getInitParameter(property);
				addPropertyValue(new PropertyValue(property, value));
				if (missingProps != null) {
					missingProps.remove(property);
				}
			}

			// Fail if we are still missing properties.
			if (!CollectionUtils.isEmpty(missingProps)) {
				throw new ServletException(
						"Initialization from ServletConfig for servlet '" + config.getServletName() +
						"' failed; the following required properties were missing: " +
						StringUtils.collectionToDelimitedString(missingProps, ", "));
			}
		}

// FrameworkServlet
@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 {
			this.webApplicationContext = initWebApplicationContext();
			//设计为子类覆盖
			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");
		}
	}

`WebApplicationContext`初始化

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
			// 在构造时注入了上下文实例
			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);
					}
					// 刷新上下文环境
					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
			// 根据contextAttribute属性加载WebApplicationContext
			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;
	}

@Nullable
	protected WebApplicationContext findWebApplicationContext() {
		String attrName = getContextAttribute();
		if (attrName == null) {
			return null;
		}
		WebApplicationContext wac =
				WebApplicationContextUtils.getWebApplicationContext(getServletContext(), attrName);
		if (wac == null) {
			throw new IllegalStateException("No WebApplicationContext found: initializer not registered?");
		}
		return wac;
	}

FrameworkServlet#createWebApplicationContextApplicationContext)

protected WebApplicationContext createWebApplicationContext(@Nullable ApplicationContext parent) {
		//获取servlet的初始化参数contextClass，没有配置默认为XmlWebApplicationContext.class
		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");
		}
		// 通过反射方式实例化contextClass
		ConfigurableWebApplicationContext wac =
				(ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);

		wac.setEnvironment(getEnvironment());
		// parent 为ContextLoadListener中创建的实例
		// 在ContextLoadListener加载的时候初始化WebApplicationContext类型的实例
		wac.setParent(parent);
		// 获取contextConfigLocation 属性，配置servlet初始化参数中。
		String configLocation = getContextConfigLocation();
		if (configLocation != null) {
			wac.setConfigLocation(configLocation);
		}
		// 初始化spring环境中包括加载配置文件等。
		configureAndRefreshWebApplicationContext(wac);

		return wac;
	}

FrameworkServlet#initWebApplicationContext 方法中的 onRefresh(wac);

org.springframework.web.servlet.DispatcherServlet#onRefresh

@Override
protected void onRefresh(ApplicationContext context) {
	initStrategies(context);
}
protected void initStrategies(ApplicationContext context) {
		// 初始化MultipartResolver
		initMultipartResolver(context);
		// 初始化LocaleResolver
		initLocaleResolver(context);
		//初始化ThemeResolver
		initThemeResolver(context);
		// 初始化HandlerMappings
		initHandlerMappings(context);
		// 初始化HandlerAdapters
		initHandlerAdapters(context);
		// 初始化HandlerExceptionResolvers
		initHandlerExceptionResolvers(context);
		// 初始化RequestToViewNameTranslator
		initRequestToViewNameTranslator(context);
		// 初始化ViewResolvers
		initViewResolvers(context);
		// 初始化FlashMapManager
		initFlashMapManager(context);
	}

处理大多类似

org.springframework.web.servlet.DispatcherServlet#initHandlerMappings

private void initHandlerMappings(ApplicationContext context) {
		this.handlerMappings = null;

		 //detect 检测
		if (this.detectAllHandlerMappings) {
			// Find all HandlerMappings in the ApplicationContext, including ancestor contexts.
			//在ApplicationContext中查找所有HandlerMappings，包括祖先上下文。
			Map<String, HandlerMapping> matchingBeans =
					BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false);
			if (!matchingBeans.isEmpty()) {
				this.handlerMappings = new ArrayList<>(matchingBeans.values());
				// We keep HandlerMappings in sorted order.
				AnnotationAwareOrderComparator.sort(this.handlerMappings);
			}
		}
		else {
			 // 没有从容器中取,
			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.
		// 如果没有找到其他映射,请确保我们至少有一个HandlerMapping，通过注册默认的HandlerMapping。
		if (this.handlerMappings == null) {
			// 默认从DispatcherServlet.properties 文件中取
			this.handlerMappings = getDefaultStrategies(context, HandlerMapping.class);
			if (logger.isDebugEnabled()) {
				logger.debug("No HandlerMappings found in servlet '" + getServletName() + "': using default");
			}
		}
	}