spring启动过程之源码跟踪（下）spring Debug

在web应用启动入口是ContextLoaderListener，它是怎么完成启动过程的呢？

首先：

public class ContextLoaderListenerextends Object implements ServletContextListener

//Bootstrap listener to start up Spring's root WebApplicationContext. Simply delegates to ContextLoader.

//This listener should be registered after Log4jConfigListener in web.xml, if the latter is used.

public abstract interface javax.servlet.ServletContextListener extends java.util.EventListener

1.ContextLoaderListener.java

    public void contextInitialized(ServletContextEvent event) {
        this.contextLoader = createContextLoader();
        this.contextLoader.initWebApplicationContext(event.getServletContext());
    }

2.ContextLoader.java

    /**
     * Initialize Spring's web application context for the given servlet context,
     * according to the "{@link #CONTEXT_CLASS_PARAM contextClass}" and
     * "{@link #CONFIG_LOCATION_PARAM contextConfigLocation}" context-params.
     * @param servletContext current servlet context
     * @return the new WebApplicationContext
     * @throws IllegalStateException if there is already a root application context present
     * @throws BeansException if the context failed to initialize
     * @see #CONTEXT_CLASS_PARAM
     * @see #CONFIG_LOCATION_PARAM
     */
    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.
33             this.context = createWebApplicationContext(servletContext, parent);
            servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context);
            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;
        }
    }

3.ContextLoader.java

    protected WebApplicationContext createWebApplicationContext(
            ServletContext servletContext, ApplicationContext parent) throws BeansException {

        Class contextClass = determineContextClass(servletContext);
        if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) {
            throw new ApplicationContextException("Custom context class [" + contextClass.getName() +
                    "] is not of type [" + ConfigurableWebApplicationContext.class.getName() + "]");
        }

        ConfigurableWebApplicationContext wac =
                (ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
        wac.setParent(parent);
        wac.setServletContext(servletContext);
        wac.setConfigLocation(servletContext.getInitParameter(CONFIG_LOCATION_PARAM));
        customizeContext(servletContext, wac);
16         wac.refresh();

        return wac;
    }

4.回到了我们上两节提到的AbstractApplicationContext.java

    public void refresh() throws BeansException, IllegalStateException {
        synchronized (this.startupShutdownMonitor) {
            // Prepare this context for refreshing.
            prepareRefresh();

            // Tell the subclass to refresh the internal bean factory.
            ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

            // Prepare the bean factory for use in this context.
            prepareBeanFactory(beanFactory);

            try {
                // Allows post-processing of the bean factory in context subclasses.
                postProcessBeanFactory(beanFactory);

                // Invoke factory processors registered as beans in the context.
                invokeBeanFactoryPostProcessors(beanFactory);

                // Register bean processors that intercept bean creation.
                registerBeanPostProcessors(beanFactory);

                // Initialize message source for this context.
                initMessageSource();

                // Initialize event multicaster for this context.
                initApplicationEventMulticaster();

                // Initialize other special beans in specific context subclasses.
                onRefresh();

                // Check for listener beans and register them.
                registerListeners();

                // Instantiate all remaining (non-lazy-init) singletons.
                finishBeanFactoryInitialization(beanFactory);

                // Last step: publish corresponding event.
                finishRefresh();
            }

            catch (BeansException ex) {
                // Destroy already created singletons to avoid dangling resources.
                beanFactory.destroySingletons();

                // Reset 'active' flag.
                cancelRefresh(ex);

                // Propagate exception to caller.
                throw ex;
            }
        }
    }

5.下面就不再赘述，详情参考上面两节