DispatcherServlet 初始化过程

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public abstract class FrameworkServlet extends HttpServletBean implements ApplicationContextAware {

    protected WebApplicationContext initWebApplicationContext() {
		WebApplicationContext rootContext =
				WebApplicationContextUtils.getWebApplicationContext(getServletContext());
		WebApplicationContext wac = null;

		// TODO 注解方式激活MVC功能时，会走到这里
		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()) {
					// 设置父容器，这个父容器时从servletContext中获取的。
					// 父容器是在 ContextLoader.initWebApplicationContext()，调用完refresh()后设置到servletContext中的。
					if (cwac.getParent() == null) {
						cwac.setParent(rootContext);
					}
					// TODO 配置、刷新WebApplicationContext，调用DispatcherServlet的init()
					configureAndRefreshWebApplicationContext(cwac);
				}
			}
		}
		// 省略非关键代码...

		return wac;
	}
}

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public abstract class FrameworkServlet extends HttpServletBean implements ApplicationContextAware {

    protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac) {
		// 设置了ApplicationContext的id，代码省略...

		wac.setServletContext(getServletContext());
		wac.setServletConfig(getServletConfig());
		wac.setNamespace(getNamespace());
		// TODO 通过监听器的方式初始化Servlet，将在WebApplicationContext.refresh()调用之后执行ContextRefreshListener
		wac.addApplicationListener(new SourceFilteringListener(wac, new ContextRefreshListener()));
		
        //省略非关键代码...

		// 这里调用了核心方法 refresh()
		wac.refresh();
	}
}

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private class ContextRefreshListener implements ApplicationListener<ContextRefreshedEvent> {

    @Override
    public void onApplicationEvent(ContextRefreshedEvent event) {
        // TODO 重点：上下文刷新事件
        FrameworkServlet.this.onApplicationEvent(event);
    }
}

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public class DispatcherServlet extends FrameworkServlet {

    protected void initStrategies(ApplicationContext context) {
		// 初始化MultipartResolver，用于处理文件上传服务，如果有文件上传，
		// 那么就会将当前的HttpServletRequest包装成DefaultMultipartHttpServletRequest，
		// 并且将每个上传的内容封装成CommonsMultipartFile对象。需要在dispatcherServlet-servlet.xml中配置文件上传解析器。
		initMultipartResolver(context);
		// 用于处理应用的国际化问题，本地化解析策略。
		initLocaleResolver(context);
		// 用于定义一个主题。
		initThemeResolver(context);
		// TODO handlerMappings的初始化
		initHandlerMappings(context);
		// TODO handlerAdapters的初始化
		initHandlerAdapters(context);
		// TODO 异常处理器的初始化，当Handler处理出错后，会通过此将错误日志记录在log文件中，默认实现类是SimpleMappingExceptionResolver。
		initHandlerExceptionResolvers(context);
		// 将指定的ViewName按照定义的RequestToViewNameTranslators替换成想要的格式。
		initRequestToViewNameTranslator(context);
		// 用于将View解析成页面。
		initViewResolvers(context);
		// 用于生成FlashMap管理器。
		initFlashMapManager(context);
	}
}

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public class DispatcherServlet extends FrameworkServlet {

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

		if (this.detectAllHandlerMappings) {
			logger.debug("detectAllHandlerMappings --> true");
			// Find all HandlerMappings in the ApplicationContext, including ancestor contexts.
			// 获取到IOC容器中所有的HandlerMapping实例映射
			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);
			}
		}
		
        // 省略非关键代码...
	}
}

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public class DispatcherServlet extends FrameworkServlet {

	private void initHandlerAdapters(ApplicationContext context) {
		this.handlerAdapters = null;

		if (this.detectAllHandlerAdapters) {
			// Find all HandlerAdapters in the ApplicationContext, including ancestor contexts.
			// 从IOC容器中获取所有的HandlerAdapter实例
			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);
			}
		}
		// 省略非关键代码...
	}
}

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public class DispatcherServlet extends FrameworkServlet {

private void initHandlerExceptionResolvers(ApplicationContext context) {
		this.handlerExceptionResolvers = null;

		if (this.detectAllHandlerExceptionResolvers) {
			// 获取所有的异常处理器
			// 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);
			}
		}
		// 省略非关键代码...
	}
}