Spring ContextLoaderListener源码分析

 当我们要自动装配ApplicationContext配置信息时候，首先在web.xml配置ContextLoaderListener，下面是部分源代码：

public class ContextLoaderListener implements ServletContextListener {

private ContextLoader contextLoader;


/**
* Initialize the root web application context.
*/
public void contextInitialized(ServletContextEvent event) {
this.contextLoader = createContextLoader();
this.contextLoader.initWebApplicationContext(event.getServletContext());//注意此处
}

protected ContextLoader createContextLoader() {
return new ContextLoader();
}

public ContextLoader getContextLoader() {
return this.contextLoader;
}

public void contextDestroyed(ServletContextEvent event) {
if (this.contextLoader != null) {
this.contextLoader.closeWebApplicationContext(event.getServletContext());
}
}

}

 

 我们主要了解下WebApplicationContext是怎么初始化出来的，首先contextInitialized(ServletContextEvent event)方法的this.contextLoader.initWebApplicationContext(event.getServletContext());进去之后我们看到

 

	public WebApplicationContext initWebApplicationContext(ServletContext servletContext)
			throws IllegalStateException, BeansException {

		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");
		if (logger.isInfoEnabled()) {
			logger.info("Root WebApplicationContext: initialization started");
		}
		long startTime = System.currentTimeMillis();

		try {
			// Determine parent for root web application context, if any.
			ApplicationContext parent = loadParentContext(servletContext);

			// Store context in local instance variable, to guarantee that
			// it is available on ServletContext shutdown.
			this.context = createWebApplicationContext(servletContext, parent);
			servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context);//注意此处
			currentContextPerThread.put(Thread.currentThread().getContextClassLoader(), this.context);

			if (logger.isDebugEnabled()) {
				logger.debug("Published root WebApplicationContext as ServletContext attribute with name [" +
						WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE + "]");
			}
			if (logger.isInfoEnabled()) {
				long elapsedTime = System.currentTimeMillis() - startTime;
				logger.info("Root WebApplicationContext: initialization completed in " + elapsedTime + " ms");
			}

			return this.context;
		}
		catch (RuntimeException ex) {
			logger.error("Context initialization failed", ex);
			servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, ex);
			throw ex;
		}
		catch (Error err) {
			logger.error("Context initialization failed", err);
			servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, err);
			throw err;
		}
	}

  

注意注意此处部分，说明当我们要得到一个WebApplicationContext只需要在ServletContext中获取属性名为WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE的常量值就可以得到一个ApplicationContext，最终可以获取spring配置文件中任意一个Bean对象

eg:

 

 

	public String execute() throws Exception {
		// TODO Auto-generated method stub
		ApplicationContext conn=(ApplicationContext)ServletActionContext.getServletContext().getAttribute(WebApplicationContext.class.getName() + ".ROOT");
		System.out.println(conn.getBean("biz"));
		return SUCCESS;
	}

  

或者直接使用org.springframework.web.context.support.WebApplicationContextUtils这个抽象的工具类来获得WebApplicationContext,该类的方法

	public static WebApplicationContext getWebApplicationContext(ServletContext sc) {
		return getWebApplicationContext(sc, WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE);
	}

 

 

 

 还有更多方法就不多介绍了，自行查看这个类的源码。