1. DispatcherServlet默认策略类
DispatcherServlet有一个静态类函数，负责从属性文件中加载默认的策略实现，静态函数和属性文件如下：
1.1. static method
private static final String DEFAULT_STRATEGIES_PATH = "DispatcherServlet.properties";
static {
// Load default strategy implementations from properties file.
// This is currently strictly internal and not meant to be customized
// by application developers.
try {
ClassPathResource resource = new ClassPathResource(DEFAULT_STRATEGIES_PATH, DispatcherServlet.class);
defaultStrategies = PropertiesLoaderUtils.loadProperties(resource);
}
catch (IOException ex) {
throw new IllegalStateException("Could not load 'DispatcherServlet.properties': " + ex.getMessage());
}
}
1.2. 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.annotation.DefaultAnnotationHandlerMapping
org.springframework.web.servlet.HandlerAdapter=org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter,\
org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter,\
org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter
org.springframework.web.servlet.HandlerExceptionResolver=org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerExceptionResolver,\
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
2. WebApplicationContext的默认实现类
DispatcherServlet调用init方法进行Servlet初始化操作，在此方法中创建了一个Web容器，默认使用的是XmlWebApplicationContext进行的实例化，那么问题来了，==在哪里进行的默认配置？==
protected WebApplicationContext createWebApplicationContext(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 + "]");
}
// 省略部分代码
ConfigurableWebApplicationContext wac =
(ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
// 省略部分代码
return wac;
}
看一下输出的日志：
DEBUG org.springframework.web.servlet.DispatcherServlet [617] - Servlet with name 'springmvc' will try to create custom WebApplicationContext context of class 'org.springframework.web.context.support.XmlWebApplicationContext', using parent context [null]
可以看到contextClass是XmlWebApplicationContext，而Class<?> contextClass = getContextClass();调用的是getContextClass方法。
再向上跟踪会发现：
public static final Class<?> DEFAULT_CONTEXT_CLASS = XmlWebApplicationContext.class;
private Class<?> contextClass = DEFAULT_CONTEXT_CLASS;
public Class<?> getContextClass() {
return this.contextClass;
}
好吧，没有什么神奇的，是定义变量并初始化时写死的。