SPRING技术内幕-笔记（七）WEB环境中的springMVC

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7.1Tomcat的web.XML对springMVC 的描述：
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dispatcherServlet定义了对应的URL的映射，context-param制定了bean的定义文件的路径，contextLoaderListener作为简历IOC容器的入口，加载IOC容器到servletContext中，即上下文。

7.2上下文在？WEB容器中的启动
在WEB容器中启动spring应用的过程：
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ContextLoaderListener是一个监听器应为实现了servletAPI的ServletContextListener，就有了contextInitialized，contextDestroyed，而IOC容器的载入过程是由ContextLoaderListener的基类ContextLoader完成的：
他们关系：
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7.3WEB容器中的上下文设置

WebApplicationContext的上下文设置：
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在这个体系中XMLWebAppliocationContext初始化过程中建立了IOC容器：

public class XmlWebApplicationContext extends AbstractRefreshableWebApplicationContext {    /** Default config location for the root context */    //bean定义文件定义为常量    public static final String DEFAULT_CONFIG_LOCATION = "/WEB-INF/applicationContext.xml";    /** Default prefix for building a config location for a namespace */      //配置文件父级路径    public static final String DEFAULT_CONFIG_LOCATION_PREFIX = "/WEB-INF/";    /** Default suffix for building a config location for a namespace */    //配置文件默认的后缀名是.XML    public static final String DEFAULT_CONFIG_LOCATION_SUFFIX = ".xml";    /**     * Loads the bean definitions via an XmlBeanDefinitionReader.     * @see org.springframework.beans.factory.xml.XmlBeanDefinitionReader     * @see #initBeanDefinitionReader     * @see #loadBeanDefinitions     */    @Override    protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {        // Create a new XmlBeanDefinitionReader for the given BeanFactory.         //使用XmlBeanDefinitionReader进行BeanDefination的解析        XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);        // Configure the bean definition reader with this context's        // resource loading environment.        beanDefinitionReader.setEnvironment(this.getEnvironment());        //因为XmlWebApplicationContext 是defaultResourceLoader的子类，因此传入this        beanDefinitionReader.setResourceLoader(this);        beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));        // Allow a subclass to provide custom initialization of the reader,        // then proceed with actually loading the bean definitions.        //允许子类为reader配置自定的初始化过程        initBeanDefinitionReader(beanDefinitionReader);        //使用定义好的XmlBeanDefinitionReader载入BeanDefinition        loadBeanDefinitions(beanDefinitionReader);    }

loadBeanDefinitions方法代码：

//有多个beanDefination定义要逐个载入    protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws IOException {        String[] configLocations = getConfigLocations();        if (configLocations != null) {            for (String configLocation : configLocations) {                reader.loadBeanDefinitions(configLocation);            }        }    }

得到Resource的路径默认是“/WEB-INF/applicationContext.xml”

    protected String[] getDefaultConfigLocations() {        if (getNamespace() != null) {            return new String[] {DEFAULT_CONFIG_LOCATION_PREFIX + getNamespace() + DEFAULT_CONFIG_LOCATION_SUFFIX};        }        else {            return new String[] {DEFAULT_CONFIG_LOCATION};        }    }

ContextLoaderListener的contextInitialized初始化：

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

我们再到他的基类ContextLoader中WEB容器的加载过程：

public WebApplicationContext initWebApplicationContext(ServletContext servletContext) {//如果已经加载会抛出异常        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!");        }        Log logger = LogFactory.getLog(ContextLoader.class);        servletContext.log("Initializing Spring root WebApplicationContext");        if (logger.isInfoEnabled()) {            logger.info("Root WebApplicationContext: initialization started");        }        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                this.context = createWebApplicationContext(servletContext);            }            if (this.context instanceof ConfigurableWebApplicationContext) {                configureAndRefreshWebApplicationContext((ConfigurableWebApplicationContext)this.context, servletContext);            }             //将创建好的上下文放在servletContext中            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.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;        }    }

createWebApplicationContext(servletContext)即实例化上下文：

    protected WebApplicationContext createWebApplicationContext(ServletContext sc) {    //探查将那个类在WEB容器中作为IOC容器        Class<?> contextClass = determineContextClass(sc);        if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) {            throw new ApplicationContextException("Custom context class [" + contextClass.getName() +                    "] is not of type [" + ConfigurableWebApplicationContext.class.getName() + "]");        }         //实例化IOC 容器        ConfigurableWebApplicationContext wac =                (ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);        return wac;    }

默认是WebApplicationContext作为容器：

    protected Class<?> determineContextClass(ServletContext servletContext) {    //CONTEXT_CLASS_PARAM是WEB.xml的配置参数        String contextClassName = servletContext.getInitParameter(CONTEXT_CLASS_PARAM);        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 {        //默认是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);            }        }    }

configureAndRefreshWebApplicationContext方法接着设置IOC的各个参数，随后通过refresh启动容器的初始化，refresh参考前边的 FileSystemXmlApplicationContext的IOC的初始化过程。

    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...                if (sc.getMajorVersion() == 2 && sc.getMinorVersion() < 5) {                    // Servlet <= 2.4: resort to name specified in web.xml, if any.                    wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +                            ObjectUtils.getDisplayString(sc.getServletContextName()));                }                else {                    wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +                            ObjectUtils.getDisplayString(sc.getContextPath()));                }            }        }        // Determine parent for root web application context, if any.        ApplicationContext parent = loadParentContext(sc);      //设置双亲上下文        wac.setParent(parent);         //设置servletcontext以及配置文件的位置参数        wac.setServletContext(sc);        String initParameter = sc.getInitParameter(CONFIG_LOCATION_PARAM);        if (initParameter != null) {            wac.setConfigLocation(initParameter);        }        customizeContext(sc, wac);        //调用refresh初始化IOC容器        wac.refresh();    }

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