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Spring IOC 源码阅读之资源定位加载

2019-11-11 05:25:31
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关于sPRing容器的启动的主要的入口是AbstractapplicationContext的refresh()方法,这个方法非常重要;

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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.              destroyBeans();                // Reset 'active' flag.              cancelRefresh(ex);                // Propagate exception to caller.              throw ex;          }      }  }        此方法中用obtainFreshBeanFactory方法间接的调用了子类(如AbstractRefreshableApplicationContext)实现的refreshBeanFctory()方法。[java] view plain copy /**      * This implementation performs an actual refresh of this context's underlying      * bean factory, shutting down the previous bean factory (if any) and      * initializing a fresh bean factory for the next phase of the context's lifecycle.      */      @Override      protected final void refreshBeanFactory() throws BeansException {          if (hasBeanFactory()) {              destroyBeans();              closeBeanFactory();          }          try {              DefaultListableBeanFactory beanFactory = createBeanFactory();              beanFactory.setSerializationId(getId());              customizeBeanFactory(beanFactory);              loadBeanDefinitions(beanFactory);              synchronized (this.beanFactoryMonitor) {                  this.beanFactory = beanFactory;              }          }          catch (IOException ex) {              throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);          }      }       refreshBeanFctory()首先实例化一个BeanFactory(DefaultListableBeanFactory),然后调用抽象方法loadBeanDifinition(DefaultListableBeanFactory beanFactory),此方法由其子类实现,比如AbstractxmlApplicationContext、XmlWebApplicationContext等。[java] view plain copy 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(this.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);  }  在这个方法中,做了以下事情:1、首先创建了一个BeanDefinitionReader的实例(XmlBeanDefinitionReader), [java] view plain copy XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);  2、设置ResorceLoader为ApplicationContext实例本身(实际上是继承了DefaultResourceLoader,所以其实这里的ResourceLoader是DefaultResourceLoader),[java] view plain copy beanDefinitionReader.setResourceLoader(this);    3、调用loadBeanDefinitions(XmlBeanDefinitionReader reader)方法。 [java] view plain copy    protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {  Resource[] configResources = getConfigResources();  if (configResources != null) {      reader.loadBeanDefinitions(configResources);  }  String[] configLocations = getConfigLocations();  if (configLocations != null) {      reader.loadBeanDefinitions(configLocations);  }  这个方法调用父类AbstractRefreshableConfigApplication的getConfigLocations方法,获取资源定义的路径,如果不是通过构造器传入的路径,则调用getDefaultConfigLocations的子类实现来获取资源定义路径(XmlWebApplicationContext)。然后调用BeanDefinitionReader的loadBeanDefinitions(String location)方法加载资源。[java] view plain copy public int loadBeanDefinitions(String location, Set<Resource> actualResources) throws BeanDefinitionStoreException {      ResourceLoader resourceLoader = getResourceLoader();      if (resourceLoader == null) {          throw new BeanDefinitionStoreException(                  "Cannot import bean definitions from location [" + location + "]: no ResourceLoader available");      }        if (resourceLoader instanceof ResourcePatternResolver) {          // Resource pattern matching available.          try {              Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location);              int loadCount = loadBeanDefinitions(resources);              if (actualResources != null) {                  for (Resource resource : resources) {                      actualResources.add(resource);                  }              }              if (logger.isDebugEnabled()) {                  logger.debug("Loaded " + loadCount + " bean definitions from location pattern [" + location + "]");              }              return loadCount;          }          catch (IOException ex) {              throw new BeanDefinitionStoreException(                      "Could not resolve bean definition resource pattern [" + location + "]", ex);          }      }      else {          // Can only load single resources by absolute URL.只能加载一个绝对路径的URL资源          Resource resource = resourceLoader.getResource(location);          int loadCount = loadBeanDefinitions(resource);          if (actualResources != null) {              actualResources.add(resource);          }          if (logger.isDebugEnabled()) {              logger.debug("Loaded " + loadCount + " bean definitions from location [" + location + "]");          }          return loadCount;      }  }  在BeanDefinitionReader的loadBeanDefinitions的方法中,首先获取前面setter的ResourceLoader对象,调用ResourseLoader对象的getResources(location)方法(这个方法会根据location判断是否是classpathResource或者URL,如果都不是调用getResourceByPath(由子类FileSystemXmlApplicationContext或AbstractRefreshableWebApplicationContext等实现返回FileSystemResource或者ServletContextResource))获取具体的资源Resource。[java] view plain copy public Resource getResource(String location) {      Assert.notNull(location, "Location must not be null");      if (location.startsWith(CLASSPATH_URL_PREFIX)) {          return new ClassPathResource(location.substring(CLASSPATH_URL_PREFIX.length()), getClassLoader());      }      else {          try {              // Try to parse the location as a URL...              URL url = new URL(location);              return new UrlResource(url);          }          catch (MalformedURLException ex) {              // No URL -> resolve as resource path.              return getResourceByPath(location);          }      }  }  FileSystemXmlApplication:[java] view plain copy        protected Resource getResourceByPath(String path) {  if (path != null && path.startsWith("/")) {      path = path.substring(1);  }  return new FileSystemResource(path);  AbstractRefreshableWebApplicationContext:[java] view plain copy protected Resource getResourceByPath(String path) {          return new ServletContextResource(this.servletContext, path);      } 
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