SpringMVC容器初始化 ContextLoaderListener

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ContextLoaderListener的作用就是启动Web容器时，自动装配ApplicationContext的配置信息。

web.xml配置

通常在web.xml中如下配置：

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<context-param>
	<param-name>contextConfigLocation</param-name>
	<param-value>classpath:spring/spring-context-test.xml</param-value>
</context-param>
<listener>
	<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>

ContextLoaderListener UML类图

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ServletContext启动后会调用ServletContextListener的contextInitialized方法。

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UML 时序图

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createWebApplicationContext

用指定的contextClass或者默认class实例化ConfigurableWebApplicationContext

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//ContextLoader
protected WebApplicationContext createWebApplicationContext(ServletContext sc) {
	Class<?> contextClass = determineContextClass(sc);
	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);
}

寻找用来实例化ConfigurableWebApplicationContext的class(determineContextClass)

先寻找web.xml 中指定的contextClass，如果没有再使用ContextLoader.properties配置的默认实现类

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//ContextLoader.java
protected Class<?> determineContextClass(ServletContext servletContext) {
	String contextClassName = servletContext.getInitParameter(CONTEXT_CLASS_PARAM);//contextClass
	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 {
		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);
		}
	}
}

其中，在ContextLoader类中有这样的静态代码块：

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static {
	// Load default strategy implementations from properties file.
	// This is currently strictly internal and not meant to be customized
	// by application developers.
	try {
	    //DEFAULT_STRATEGIES_PATH = "ContextLoader.properties";
		ClassPathResource resource = new ClassPathResource(DEFAULT_STRATEGIES_PATH, ContextLoader.class);
		defaultStrategies = PropertiesLoaderUtils.loadProperties(resource);
	}
	catch (IOException ex) {
		throw new IllegalStateException("Could not load 'ContextLoader.properties': " + ex.getMessage());
	}
}

ContextLoader.properties文件如下，配置了WebApplicationContext接口的默认实现类

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# Default WebApplicationContext implementation class for ContextLoader.
# Used as fallback when no explicit context implementation has been specified as context-param.
# Not meant to be customized by application developers.

org.springframework.web.context.WebApplicationContext=org.springframework.web.context.support.XmlWebApplicationContext

loadParentContext

日后分析

configureAndRefreshWebApplicationContext

主要功能是调用AbstractApplicationContext的refresh方法，加载bean

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protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac, ServletContext sc) {
	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
		String idParam = sc.getInitParameter(CONTEXT_ID_PARAM);
		if (idParam != null) {
			wac.setId(idParam);
		}
		else {
			// Generate default id...
			wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +
					ObjectUtils.getDisplayString(sc.getContextPath()));
		}
	}

	wac.setServletContext(sc);
	String configLocationParam = sc.getInitParameter(CONFIG_LOCATION_PARAM);
	if (configLocationParam != null) {
		wac.setConfigLocation(configLocationParam);
	}

	// 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(sc, null);
	}

	customizeContext(sc, wac);
	wac.refresh();
}