Spring MVC(三)-----FrameworkServlet

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引言

HttpServletBean完成的工作非常简单，FrameworkServlet完成的工作也不复杂，主要就是创建SpringMVC的IOC容器。但是debug 没有配置文件的springboot项目发现，最要的工作还是调用了DispatcherServlet重写的onRefresh方法

上一篇

Spring MVC(二)-----HttpServletBean
https://blog.csdn.net/yueloveme/article/details/89643980

正文

FrameworkServlet类的设计目的就是用来建立一个和Servlet关联的Spring容器上下文并将其注册到ServletContext中。
debug过程中没有遇到需要FrameworkServlet来创建容器的情况，在AbstractApplicationContext中refresh方法中创建Spring的IOC容器是在SpringMVC初始化之前进行的，而且并不是项目启动就会初始化SpringMVC而是第一次调用的时候会进行初始化，这是目前观察到的如有不正确欢迎指正

initServletBean

/**
	 * 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 {
			this.webApplicationContext = initWebApplicationContext();
			无具体实现
			initFrameworkServlet();
		}
		catch (ServletException | 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");
		}
	}

initWebApplicationContext

/**
	 * Initialize and publish the WebApplicationContext for this servlet.
	 * 
Delegates to {@link #createWebApplicationContext} for actual creation
	 * of the context. Can be overridden in subclasses.
	 * @return the WebApplicationContext instance
	 * @see #FrameworkServlet(WebApplicationContext)
	 * @see #setContextClass
	 * @see #setContextConfigLocation
	 */
	 初始化和发布web应用上下文
	protected WebApplicationContext initWebApplicationContext() {
	获取Spring的IOC容器 SpringIOC容器是先于SpringMVC容器创建的，要把rootContext
	当做父容器
		WebApplicationContext rootContext =
				WebApplicationContextUtils.getWebApplicationContext(getServletContext());
		WebApplicationContext wac = null;
如果webApplicationContext已经不为空，表示这个Servlet类是通过编程式注册到容器中的
(Servlet 3.0 +中的ServletContext.addServlet（）)，上下文也由编程式传入。若这个传
入的上下文还没有被初始化，将rootContext上下文设置为它的父上下文，然后将其初始化，否
则直接使用。
		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
			如果为空，说明该Servlet不是由编程式注册到容器中的，在ServletContext中
			查找上下文，查找得到
			说明上下文已经以别的方式初始化并注册在contextAttribute下，直接使用
			wac = findWebApplicationContext();
		}
		if (wac == null) {
			// No context instance is defined for this servlet -> create a local one
			此时还为空，调用以下方法创建一个全新的以rootContext为父上下文的上下
			文，作为SpringMVC配置元素的上下文
			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.
			DispatcherServlet具体实现，初始化一系列属性
			onRefresh(wac);
		}

		if (this.publishContext) {
			// Publish the context as a servlet context attribute.
			将这个上下文发布到ServletContext中
			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;
	}

findWebApplicationContext

从当前容器中查找SpringMVC容器
/**
	 * Retrieve a {@code WebApplicationContext} from the {@code ServletContext}
	 * attribute with the {@link #setContextAttribute configured name}. The
	 * {@code WebApplicationContext} must have already been loaded and stored in the
	 * {@code ServletContext} before this servlet gets initialized (or invoked).
	 * 
Subclasses may override this method to provide a different
	 * {@code WebApplicationContext} retrieval strategy.
	 * @return the WebApplicationContext for this servlet, or {@code null} if not found
	 * @see #getContextAttribute()
	 */
	@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;
	}

createWebApplicationContext

创建SpringMVC容器
/**
	 * Instantiate the WebApplicationContext for this servlet, either a default
	 * {@link org.springframework.web.context.support.XmlWebApplicationContext}
	 * or a {@link #setContextClass custom context class}, if set.
	 * 
This implementation expects custom contexts to implement the
	 * {@link org.springframework.web.context.ConfigurableWebApplicationContext}
	 * interface. Can be overridden in subclasses.
	 * 
Do not forget to register this servlet instance as application listener on the
	 * created context (for triggering its {@link #onRefresh callback}, and to call
	 * {@link org.springframework.context.ConfigurableApplicationContext#refresh()}
	 * before returning the context instance.
	 * @param parent the parent ApplicationContext to use, or {@code null} if none
	 * @return the WebApplicationContext for this servlet
	 * @see org.springframework.web.context.support.XmlWebApplicationContext
	 */
	protected WebApplicationContext createWebApplicationContext(@Nullable 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");
		}
		实例化IOC容器
		ConfigurableWebApplicationContext wac =
				(ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
		设置IOC容器相关属性
		wac.setEnvironment(getEnvironment());
		设置parent
		wac.setParent(parent);
		String configLocation = getContextConfigLocation();
		if (configLocation != null) {
			wac.setConfigLocation(configLocation);
		}
		初始化springMVC各种的相关配置，各种注入的Controller，配置文件
		configureAndRefreshWebApplicationContext(wac);

		return wac;
	}

configureAndRefreshWebApplicationContext

配置或者刷新应用上下文
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SpringMVC 属性
		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);
		初始化springMVC各种的相关配置，各种注入的Controller，配置文件
		wac.refresh();
	}