19、SpringBoot 源码分析 - DispatcherServlet初始化一

基本流程图，方便查看

initLocaleResolver

看起来好像一样的，但是找不到localeResolver之后会调用getDefaultStrategy找，也就是说自动配置没有。

/** Well-known name for the LocaleResolver object in the bean factory for this namespace. */
	public static final String LOCALE_RESOLVER_BEAN_NAME = "localeResolver";

	private void initLocaleResolver(ApplicationContext context) {
   
     
		try {
   
     
			this.localeResolver = context.getBean(LOCALE_RESOLVER_BEAN_NAME, LocaleResolver.class);
			if (logger.isTraceEnabled()) {
   
     
				logger.trace("Detected " + this.localeResolver);
			}
			else if (logger.isDebugEnabled()) {
   
     
				logger.debug("Detected " + this.localeResolver.getClass().getSimpleName());
			}
		}
		catch (NoSuchBeanDefinitionException ex) {
   
     
			// We need to use the default.
			this.localeResolver = getDefaultStrategy(context, LocaleResolver.class);
			if (logger.isTraceEnabled()) {
   
     
				logger.trace("No LocaleResolver '" + LOCALE_RESOLVER_BEAN_NAME +
						"': using default [" + this.localeResolver.getClass().getSimpleName() + "]");
			}
		}
	}

getDefaultStrategy

从默认配置里获取strategyInterface的集合，但是只能是一个，因为容器里没有才会到这里来，这里完全是可以有的，所以只能一个，当然没有也会报错。所以这里应该可以想到为什么一定有，那肯定是默认配置好啦，不在自动配置里，马上揭晓。

	protected <T> T getDefaultStrategy(ApplicationContext context, Class<T> strategyInterface) {
   
     
		List<T> strategies = getDefaultStrategies(context, strategyInterface);
		if (strategies.size() != 1) {
   
     
			throw new BeanInitializationException(
					"DispatcherServlet needs exactly 1 strategy for interface [" + strategyInterface.getName() + "]");
		}
		return strategies.get(0);
	}

DispatcherServlet的初始化静态代码块

前面创建DispatcherServlet的时候没讲，这里来讲比较合适，刚好可以理解，可以用到，下面这段静态代码块做的就是读取DispatcherServlet.properties到defaultStrategies ：

private static final String DEFAULT_STRATEGIES_PATH = "DispatcherServlet.properties";
private static final Properties defaultStrategies;
...
static {
   
     
	
		try {
   
     //获取默认的处理器和解析器配置
			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());
		}
	}

DispatcherServlet的组件默认配置

DispatcherServlet.properties在哪里呢，其实就是在spring-webmvc-5.2.5.RELEASE.jar的org\springframework\web\servlet\DispatcherServlet.properties：

里面其实就是默认的配置，我们可以看到LocaleResolver只有一个：

# 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

getDefaultStrategies

直接从defaultStrategies获取对应的属性，然后用逗号分隔符分割，然后反射出类型，用容器来实例化，然后返回。

protected <T> List<T> getDefaultStrategies(ApplicationContext context, Class<T> strategyInterface) {
   
     
		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 new LinkedList<>();
		}
	}

结果也就是默认配的那个：

好了，今天就到这里了，希望对学习理解有帮助，大神看见勿喷，仅为自己的学习理解，能力有限，请多包涵。