springmvc源码解析之配置加载ContextLoadListener第二章

主入口初始化

org.springframework.web.context.ContextLoader#initWebApplicationContext

public WebApplicationContext initWebApplicationContext(ServletContext servletContext) {
		// 获取root上下文对象
		if (servletContext.getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE) != null) {
			throw new IllegalStateException(
					"Cannot initialize context because there is already a root application context present - " +
					"check whether you have multiple ContextLoader* definitions in your web.xml!");
		}
		servletContext.log("Initializing Spring root WebApplicationContext");
		Log logger = LogFactory.getLog(ContextLoader.class);
		if (logger.isInfoEnabled()) {
			logger.info("Root WebApplicationContext: initialization started");
		}
		// 启动开始
		long startTime = System.currentTimeMillis();
		try {
			// Store context in local instance variable, to guarantee that
			// it is available on ServletContext shutdown.
			if (this.context == null) {
				// 创建上下文对象
				this.context = createWebApplicationContext(servletContext);
			}
			// ConfigurableWebApplicationContext 该类主要是跟bean相关
			if (this.context instanceof ConfigurableWebApplicationContext) {
				//
				ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) this.context;
				if (!cwac.isActive()) {
					// The context has not yet been refreshed -> provide services such as
					// setting the parent context, setting the application context id, etc
					// 当前上下文没有被加载过那么就对他进行处理
					if (cwac.getParent() == null) {
						// The context instance was injected without an explicit parent ->
						// determine parent for root web application context, if any.
						ApplicationContext parent = loadParentContext(servletContext);
						// 设置父上下文对象
						cwac.setParent(parent);
					}
					//
					configureAndRefreshWebApplicationContext(cwac, servletContext);
				}
			}
			servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context);

			ClassLoader ccl = Thread.currentThread().getContextClassLoader();
			if (ccl == ContextLoader.class.getClassLoader()) {
				currentContext = this.context;
			}
			else if (ccl != null) {
				currentContextPerThread.put(ccl, this.context);
			}

			if (logger.isInfoEnabled()) {
				long elapsedTime = System.currentTimeMillis() - startTime;
				logger.info("Root WebApplicationContext initialized in " + elapsedTime + " ms");
			}

			return this.context;
		}
		catch (RuntimeException | Error ex) {
			logger.error("Context initialization failed", ex);
			servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, ex);
			throw ex;
		}
	}
  • 获取根上下文对象servletContext.getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE)
  • 创建一个子上下文对象 createWebApplicationContext
  • ConfigurableWebApplicationContext 判断是不是这个类的目前就是说明当前类是否是可配置的,然后创建复制当前上下文的父上下文对象。

  • 初始化web上下文对象
	protected WebApplicationContext createWebApplicationContext(ServletContext sc) {
		//加载该类通过当前线程的类加载器
		Class<?> contextClass = determineContextClass(sc);
		if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) {
			throw new ApplicationContextException("Custom context class [" + contextClass.getName() +
					"] is not of type [" + ConfigurableWebApplicationContext.class.getName() + "]");
		}
		// 对应的实例信息
		return (ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
	}
  • 正常初始化过程
protected Class<?> determineContextClass(ServletContext servletContext) {
		// 第一步: 获取参数
		String contextClassName = servletContext.getInitParameter(CONTEXT_CLASS_PARAM);
		if (contextClassName != null) {
			try {
				// 这里做初始化的操作
				return ClassUtils.forName(contextClassName, ClassUtils.getDefaultClassLoader());
			}
			catch (ClassNotFoundException ex) {
				throw new ApplicationContextException(
						"Failed to load custom context class [" + contextClassName + "]", ex);
			}
		}
		else {
			// 第二步: 如果无法获取到 WebApplicationContext
			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);
			}
		}
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, ContextLoader.class);
			defaultStrategies = PropertiesLoaderUtils.loadProperties(resource);
		}
		catch (IOException ex) {
			throw new IllegalStateException("Could not load 'ContextLoader.properties': " + ex.getMessage());
		}
	}
  • 过滤掉文件
public static Properties loadProperties(Resource resource) throws IOException {
		Properties props = new Properties();
		fillProperties(props, resource);
		return props;
	}
  • 第一个文件以xml结尾了,和其他的properties文件
public static void fillProperties(Properties props, Resource resource) throws IOException {
		InputStream is = resource.getInputStream();
		try {
			String filename = resource.getFilename();
			if (filename != null && filename.endsWith(XML_FILE_EXTENSION)) {
				props.loadFromXML(is);
			}
			else {
				props.load(is);
			}
		}
		finally {
			is.close();
		}
	}

org.springframework.web.context.ContextLoader#loadParentContext

  • 发现这个类为空实现
ApplicationContext parent = loadParentContext(servletContext);

org.springframework.web.context.ContextLoader#configureAndRefreshWebApplicationContext 配置或者刷新web上下文

	configureAndRefreshWebApplicationContext(cwac, servletContext);
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
			//第一步: 获取到初始发参数
			String idParam = sc.getInitParameter(CONTEXT_ID_PARAM);
			if (idParam != null) {
				wac.setId(idParam);
			}
			//第二步: 如果没有获取到,那么就产生没人的id
			else {
				// Generate default id...
				wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +
						ObjectUtils.getDisplayString(sc.getContextPath()));
			}
		}
        // 第三步: 设置上下文对象
		wac.setServletContext(sc);
		// 第四步: 获取配置文件路径 contextConfigLocation,配置文件可以是多个的,用,换行分开,可以用占位符
		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
		// 第五步: 设置环境变量
		ConfigurableEnvironment env = wac.getEnvironment();
		if (env instanceof ConfigurableWebEnvironment) {
			((ConfigurableWebEnvironment) env).initPropertySources(sc, null);
		}
         // 第六步: 加载子类实现的上下文
		customizeContext(sc, wac);
		//  第七步: 上下文刷新
		wac.refresh();
	}


  • 获取到初始发参数
  • 如果没有获取到,那么就产生一个的id
  • 设置上下文对象
  • 获取配置文件路径 contextConfigLocation,配置文件可以是多个的,用,换行分开,可以用占位符
  • 设置环境变量
  • 加载子类实现的上下文
  • 上下文刷新
	customizeContext(sc, wac);
protected void customizeContext(ServletContext sc, ConfigurableWebApplicationContext wac) {
		//找到上下文初始化类 ->
		List<Class<ApplicationContextInitializer<ConfigurableApplicationContext>>> initializerClasses =
				determineContextInitializerClasses(sc);
         判断上下文初始化类是否是ConfigurableWebApplicationContext类型
		for (Class<ApplicationContextInitializer<ConfigurableApplicationContext>> initializerClass : initializerClasses) {
			Class<?> initializerContextClass =
					GenericTypeResolver.resolveTypeArgument(initializerClass, ApplicationContextInitializer.class);
			if (initializerContextClass != null && !initializerContextClass.isInstance(wac)) {
				throw new ApplicationContextException(String.format(
						"Could not apply context initializer [%s] since its generic parameter [%s] " +
						"is not assignable from the type of application context used by this " +
						"context loader: [%s]", initializerClass.getName(), initializerContextClass.getName(),
						wac.getClass().getName()));
			}
			// 初始化上下文初始化类
			this.contextInitializers.add(BeanUtils.instantiateClass(initializerClass));
		}

		AnnotationAwareOrderComparator.sort(this.contextInitializers);
		for (ApplicationContextInitializer<ConfigurableApplicationContext> initializer : this.contextInitializers) {
			// 调用初始化器的初始化方法,初始化器可以自己实现
			initializer.initialize(wac);
		}
	}

org.springframework.web.context.ContextLoader#determineContextInitializerClasses

protected List<Class<ApplicationContextInitializer<ConfigurableApplicationContext>>>
			determineContextInitializerClasses(ServletContext servletContext) {

		List<Class<ApplicationContextInitializer<ConfigurableApplicationContext>>> classes =
				new ArrayList<>();

		String globalClassNames = servletContext.getInitParameter(GLOBAL_INITIALIZER_CLASSES_PARAM);
		if (globalClassNames != null) {
			for (String className : StringUtils.tokenizeToStringArray(globalClassNames, INIT_PARAM_DELIMITERS)) {
				classes.add(loadInitializerClass(className));
			}
		}

		String localClassNames = servletContext.getInitParameter(CONTEXT_INITIALIZER_CLASSES_PARAM);
		if (localClassNames != null) {
			for (String className : StringUtils.tokenizeToStringArray(localClassNames, INIT_PARAM_DELIMITERS)) {
				classes.add(loadInitializerClass(className));
			}
		}

		return classes;
	}

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转载自blog.csdn.net/qq_30561643/article/details/103804357