Context层级的问题,后面文章应该曾经说分明了。

只不过,后面文章是以注解形式举例说明的,通过配置形式怎么体现Context层级呢?有必要也说一下,毕竟当初很多我的项目都是基于xml配置实现的。

web.xml

基于配置的Spring MVC的入口就是web.xml文件,毕竟web.xml是基于web的利用的先人入口......

<?xml version="1.0" encoding="UTF-8"?><web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"         xmlns="http://xmlns.jcp.org/xml/ns/javaee"         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"         id="WebApp_ID" version="3.1">  <!--1、启动Spring的容器 -->  <context-param>    <param-name>contextConfigLocation</param-name>    <param-value>classpath:applicationContext.xml</param-value>  </context-param>  <listener>    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>  </listener>

肯定要搞清楚的是,context-param配置是用来指定的Spring容器的配置文件所在门路的。必须是和ContextLoaderListener一起配合起作用的。ContextLoaderListener读取context-param的配置来实现Spring IoC容器的初始化的。

Spring IoC容器和Spring MVC的Servlet Web ApplicationContext容器不是必须要离开的,也能够配置为同一个容器。

比方以上配置不指定(不配置Spring IoC容器),也就是去掉contextConfigLocation以及ContextLoaderListener,让Spring MVC的容器担负起Spring IoC容器的职责,也是能够的。

web.xml上面持续配置spring MVC的xml文件所在门路,DispathcerServlet初始化的时候会读取。

  <!--2、springmvc的前端控制器,拦挡所有申请 -->  <servlet>    <servlet-name>dispatcherServlet</servlet-name>    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>    <init-param>      <param-name>contextConfigLocation</param-name>      <param-value>classpath:springmvc.xml</param-value>    </init-param>    <load-on-startup>1</load-on-startup>  </servlet>  <servlet-mapping>    <servlet-name>dispatcherServlet</servlet-name>    <url-pattern>/</url-pattern>  </servlet-mapping>

Spring-mvc.xml

名字是能够在web.xml文件中指定的,不指定的话默认就是dispatcherServlet名-dispatcher.xml(须要读一下SpringMVC源码确认)。

如果你想要Spring IoC容器和Spring MvC的web applicationContext容器离开的话,就在Spring-mvc.xml文件中指定包扫描门路仅扫描controller,否则,全扫描即可。反之,Spring Ioc容器存在的话,配置文件的扫描门路也要排除掉Controller的扫描:

    <context:component-scan base-package="org.example.service">        <context:exclude-filter type="annotation"                                expression="org.springframework.stereotype.Controller" />    </context:component-scan>

Servlet和根容器的关系

下图高深莫测的阐明了两者之间的关系:

Servlet容器寄存Controller、VIewResolver、HanderMapping等DispatcherServlet的相干对象,根容器能够寄存其余Service、Repositories等对象。

一个DispatcherServlet能够对应的有一个Servlet WebApplicationContext容器,一个Web利用能够有多个DispatcherServlet(这种利用其实比拟少见),所以一个利用能够有多个Servlet WebApplicationContext容器。然而个别状况下,即便有多个Servlet容器,一个利用也心愿只有一个根容器,以便在不同的Servlet容器之间共享根容器的对象。

根容器初始化过程

xml配置文件的状况下,根容器要依附ContextLoaderListener来初始化。ContextLoaderListener是Spring MVC实现的ServletContextListener接口的实现类,ServletContextListener是Java Servlet的接口。Servlet规范约定,在Servlet容器初始化的过程中,会回调ServletContextListener接口的contextInitialized办法。

所以如果咱们在web.xml文件中配置了ContextLoaderListener,那么,Tomcat在Servlet容器初始化的过程中就会回调ContextLoaderListener的contextInitialized办法:

    @Override    public void contextInitialized(ServletContextEvent event) {        initWebApplicationContext(event.getServletContext());    }

该办法会调用initWebApplicationContext办法,这个办法咱们在后面文章中其实曾经剖析过了,咱们再来看一下:

public WebApplicationContext initWebApplicationContext(ServletContext servletContext) {        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");        }        long startTime = System.currentTimeMillis();        try {            // Store context in local instance variable, to guarantee that            // it is available on ServletContext shutdown.            if (this.context == null) {                this.context = createWebApplicationContext(servletContext);            }            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                    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);                }            }      ...省略n行代码

最终会调用到configureAndRefreshWebApplicationContext办法:

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);        }      ...

configureAndRefreshWebApplicationContext办法会读取web.xml中contextConfigLocation配置,Spring IoC容器的初始化配置文件applicationContext.xml文件名、曾经所在位置就是在这儿被读入的。

读入配置文件信息之后,调用refresh办法:

        // 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();    }

refresh办法是Spring framework的办法,具体就不在这儿深入研究了,咱们只是简略跟中一下配置文件的加载过程:

    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();            ...

在refresh办法的obtainFreshBeanFactory()办法中:

    protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {        refreshBeanFactory();        return getBeanFactory();    }

持续跟踪refreshBeanFactory();办法:

@Override    protected final void refreshBeanFactory() throws BeansException {        if (hasBeanFactory()) {            destroyBeans();            closeBeanFactory();        }        try {            DefaultListableBeanFactory beanFactory = createBeanFactory();            beanFactory.setSerializationId(getId());            customizeBeanFactory(beanFactory);            loadBeanDefinitions(beanFactory);            this.beanFactory = beanFactory;        }        catch (IOException ex) {            throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);        }    }

持续跟踪,loadBeanDefinitions(beanFactory);办法,会调用到XmlWebApplicationContext类中:

@Override    protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {        // Create a new XmlBeanDefinitionReader for the given BeanFactory.        XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);        // Configure the bean definition reader with this context's        // resource loading environment.        beanDefinitionReader.setEnvironment(getEnvironment());        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.        initBeanDefinitionReader(beanDefinitionReader);        loadBeanDefinitions(beanDefinitionReader);    }

最初一个办法调用,loadBeanDefinitions办法:

    protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws IOException {        String[] configLocations = getConfigLocations();        if (configLocations != null) {            for (String configLocation : configLocations) {                reader.loadBeanDefinitions(configLocation);            }        }    }

终于发现了依据configLocation通过loadBeanDefinitions办法读取配置文件、调用beandefinition的代码逻辑。

能够发现代码是能够反对多个配置文件的!

从代码的角度,咱们也实现了xml配置形式下,SpringMVC与spring framework集成,实现spring Ioc容器的初始化过程!

与后面两篇文:Spring MVC 四:Context层级/Spring MVC 五 - Spring MVC的配置和DispatcherServlet初始化过程:Context层级联合,咱们就实现了基于注解的、以及基于xml配置文件两种形式下的Spring MVC框架下,Spring IoC容器的初始化代码的剖析!

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