Spring源碼(3)Context篇之ConfigurableWebApplicationContext

上一篇講解了Spring通過ContextLoader類的initWebApplicationContext方法創建的WebApplicationContext實爲XmlWebApplicationContext實例

再看initWebApplicationContext方法的源碼：

/**
 *  爲了講重點，省略了部分源碼
 */
public WebApplicationContext initWebApplicationContext(ServletContext servletContext) {
 	...
	try {
		// Store context in local instance variable, to guarantee that
		// it is available on ServletContext shutdown.
		if (this.context == null) {
			this.context = createWebApplicationContext(servletContext);		//312行
		}
		if (this.context instanceof ConfigurableWebApplicationContext) {		//314行
			//重點就是這裏的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
				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);
					cwac.setParent(parent);
				}
				configureAndRefreshWebApplicationContext(cwac, servletContext);
			}
		}
		...
		return this.context;
	}
   ...
}

從initWebApplicationContext方法可以看出來，有判斷XmlWebApplicationContext是否屬於ConfigurableWebApplicationContext類型

來看一下ConfigurableApplicationContext的源碼

 * Copyright 2002-2014 the original author or authors.

package org.springframework.web.context;

import javax.servlet.ServletConfig;
import javax.servlet.ServletContext;

import org.springframework.context.ConfigurableApplicationContext;

/**
 * Interface to be implemented by configurable web application contexts.
 * Supported by {@link ContextLoader} and
 * {@link org.springframework.web.servlet.FrameworkServlet}.
 *
 * <p>Note: The setters of this interface need to be called before an
 * invocation of the {@link #refresh} method inherited from
 * {@link org.springframework.context.ConfigurableApplicationContext}.
 * They do not cause an initialization of the context on their own.
 *
 * @author Juergen Hoeller
 * @since 05.12.2003
 * @see #refresh
 * @see ContextLoader#createWebApplicationContext
 * @see org.springframework.web.servlet.FrameworkServlet#createWebApplicationContext
 */
public interface ConfigurableWebApplicationContext extends WebApplicationContext, ConfigurableApplicationContext {

	/**
	 * Prefix for ApplicationContext ids that refer to context path and/or servlet name.
	 */
	String APPLICATION_CONTEXT_ID_PREFIX = WebApplicationContext.class.getName() + ":";

	/**
	 * Name of the ServletConfig environment bean in the factory.
	 * @see javax.servlet.ServletConfig
	 */
	String SERVLET_CONFIG_BEAN_NAME = "servletConfig";


	/**
	 * Set the ServletContext for this web application context.
	 * <p>Does not cause an initialization of the context: refresh needs to be
	 * called after the setting of all configuration properties.
	 * @see #refresh()
	 */
	void setServletContext(ServletContext servletContext);

	/**
	 * Set the ServletConfig for this web application context.
	 * Only called for a WebApplicationContext that belongs to a specific Servlet.
	 * @see #refresh()
	 */
	void setServletConfig(ServletConfig servletConfig);

	/**
	 * Return the ServletConfig for this web application context, if any.
	 */
	ServletConfig getServletConfig();

	/**
	 * Set the namespace for this web application context,
	 * to be used for building a default context config location.
	 * The root web application context does not have a namespace.
	 */
	void setNamespace(String namespace);

	/**
	 * Return the namespace for this web application context, if any.
	 */
	String getNamespace();

	/**
	 * Set the config locations for this web application context in init-param style,
	 * i.e. with distinct locations separated by commas, semicolons or whitespace.
	 * <p>If not set, the implementation is supposed to use a default for the
	 * given namespace or the root web application context, as appropriate.
	 */
	void setConfigLocation(String configLocation);

	/**
	 * Set the config locations for this web application context.
	 * <p>If not set, the implementation is supposed to use a default for the
	 * given namespace or the root web application context, as appropriate.
	 */
	void setConfigLocations(String... configLocations);

	/**
	 * Return the config locations for this web application context,
	 * or {@code null} if none specified.
	 */
	String[] getConfigLocations();

}

可以看出來

1. ConfigurableWebApplicationContext是個接口，而且顧名思義：可配置的WebApplicationContext
2. ConfigurableWebApplicationContext類定義了8個方法，主要是關於context和config的get和set

其實就是在上面講到的ContextLoader類的initWebApplicationContext方法，接着調用了configureAndRefreshWebApplicationContext方法，查看其源碼：

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();
}

其中String configLocationParam = sc.getInitParameter(CONFIG_LOCATION_PARAM);代碼就是獲取我們經常在web.xml裏配置的contextConfigLocation

<context-param>
	<param-name>contextConfigLocation</param-name>
	<param-value>classpath*:/spring/*.xml</param-value>
</context-param>

若web.xml配置的是上面的代碼，那configLocationParam的值就是classpath*:/spring/*.xml，該值接着就被set到AbstractRefreshableConfigApplicationContext類的configLocations變量裏，講到這裏就不得不貼一下類關係圖了