初探spring applicationContext

初探spring applicationContext在web容器中加载过程

首先从WEB.XML入手

==>web.xml

 

<context-param>
    <param-name>webAppRootKey</param-name>
    <param-value>task.root</param-value>
  </context-param>
  <!-- 定义SPRING配置文件 -->
  
   <context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>/WEB-INF/taskContext*.xml</param-value>
  </context-param>
  
  <context-param>
    <param-name>log4jConfigLocation</param-name>
    <param-value>/WEB-INF/log4j.properties</param-value>
  </context-param>
  <!-- 定义LOG4J监听器 -->
  <listener>
    <listener-class>org.springframework.web.util.Log4jConfigListener</listener-class>
  </listener>

  <!-- 定义SPRING监听器 -->

  <listener>
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
  </listener>

进入contextLoaderListener看看到底加载时做了甚么
==>org.springframework.web.context.ContextLoaderListener

public class ContextLoaderListener implements ServletContextListener {

  private ContextLoader contextLoader;

  /**
   * Initialize the root web application context.
   */
//当WEB上下文初始化时,系统会调用此方法
  public void contextInitialized(ServletContextEvent event) {
    this.contextLoader = createContextLoader();


    //监听到WEB上下文初始化的时候执行SPRING上下文contextLoader的初始化工作
    this.contextLoader.initWebApplicationContext(event.getServletContext());

  }

  /**
   * Create the ContextLoader to use. Can be overridden in subclasses.
   * @return the new ContextLoader
   */
  protected ContextLoader createContextLoader() {
    return new ContextLoader();
  }

  /**
   * Return the ContextLoader used by this listener.
   */
  public ContextLoader getContextLoader() {
    return contextLoader;
  }

  /**
   * Close the root web application context.
   */
  public void contextDestroyed(ServletContextEvent event) {
    if (this.contextLoader != null) {
      this.contextLoader.closeWebApplicationContext(event.getServletContext());
    }
  }

}

看一下是怎么来初始化webapplicationContext的
==>contextLoader.initWebApplicationContext

 

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!");
    }

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

    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.


      //创建web上下文
      this.context = createWebApplicationContext(servletContext, parent);
      servletContext.setAttribute(
          WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context);


      if (logger.isInfoEnabled()) {
        logger.info("Using context class [" + this.context.getClass().getName() +
            "] for root WebApplicationContext");
      }
      if (logger.isDebugEnabled()) {
        logger.debug("Published root WebApplicationContext [" + this.context +
            "] 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;
    }
  }

==>contextLoader.createWebApplicationContext(servletContext, parent);

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

    //根据servletContext来决定要实例化的WebApplicationContext
    Class contextClass = determineContextClass(servletContext);
    if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) {
      throw new ApplicationContextException("Custom context class [" + contextClass.getName() +
          "] is not of type ConfigurableWebApplicationContext");
    }
    ConfigurableWebApplicationContext wac =
        (ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
    wac.setParent(parent);
    wac.setServletContext(servletContext);

    //得到WEB.XML中设置的SPRING配置文件位置
    String configLocation = servletContext.getInitParameter(CONFIG_LOCATION_PARAM);
    if (configLocation != null) {
      //把配置文件分段后设置到WebApplicationContext的ConfigLocations中
      wac.setConfigLocations(StringUtils.tokenizeToStringArray(configLocation,
          ConfigurableWebApplicationContext.CONFIG_LOCATION_DELIMITERS));
    }
    //刷新WebApplicationContext
    wac.refresh();

    return wac;
  }

==>contextLoader.determineContextClass(servletContext);

protected Class determineContextClass(ServletContext servletContext) throws ApplicationContextException {

    //获得需要实例化的CONTEXT类名,在web.xml中有设置,如果没有设置,那么为空
    String contextClassName = servletContext.getInitParameter(CONTEXT_CLASS_PARAM);
    if (contextClassName != null) {
      try {
        return ClassUtils.forName(contextClassName);
      }
      catch (ClassNotFoundException ex) {
        throw new ApplicationContextException(
            "Failed to load custom context class [" + contextClassName + "]", ex);
      }
    }
    //如果在spring web.xml中没有设置context类位置,那么取得默认context
    else {
      //取得defaultStrategies配置文件中的WebApplicationContext属性
      contextClassName = defaultStrategies.getProperty(WebApplicationContext.class.getName());
      try {
        return ClassUtils.forName(contextClassName);
      }
      catch (ClassNotFoundException ex) {
        throw new ApplicationContextException(
            "Failed to load default context class [" + contextClassName + "]", ex);
      }
    }

  }

SPRING上下文默认的策略是甚么呢?
==>contextLoader.defaultStrategies

  private static final Properties defaultStrategies;

  static {
    // Load default strategy implementations from properties file.
    // This is currently strictly internal and not meant to be customized
    // by application developers.
    try {

      //设置classpath为contextLoader同级目录
      ClassPathResource resource = new ClassPathResource(DEFAULT_STRATEGIES_PATH, ContextLoader.class);
      //加载该目录下的所有properties文件
      defaultStrategies = PropertiesLoaderUtils.loadProperties(resource);

    }
    catch (IOException ex) {
      throw new IllegalStateException("Could not load 'ContextLoader.properties': " + ex.getMessage());
    }
  }

找到同级目录下的配置文件
==>ContextLoader.properties

# Default WebApplicationContext implementation class for ContextLoader.
# Used as fallback when no explicit context implementation has been specified as context-param.
# Not meant to be customized by application developers.


#默认的WebApplicationContext为org.springframework.web.context.support.XmlWebApplicationContext
org.springframework.web.context.WebApplicationContext=org.springframework.web.context.support.XmlWebApplicationContext

==>org.springframework.web.context.support.XmlWebApplicationContext

public class XmlWebApplicationContext extends AbstractRefreshableWebApplicationContext {

  /** Default config location for the root context */


  //配置了默认的spring配置文件
  public static final String DEFAULT_CONFIG_LOCATION = "/WEB-INF/applicationContext.xml";


  //配置文件默认BUILD路径
  public static final String DEFAULT_CONFIG_LOCATION_PREFIX = "/WEB-INF/";

  //配置文件默认后缀名
  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
   */
  //获得bean配置
  protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws IOException {
    //从BEAN工厂获得一个XmlBeanDefinitionReader 来读取SPRING配置文件
    XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);

    //设置beanDefinitionReader服务于当前CONTEXT
    // resource loading environment.
    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);

    //读取配置文件
    loadBeanDefinitions(beanDefinitionReader);

  }

  /**
   * Initialize the bean definition reader used for loading the bean
   * definitions of this context. Default implementation is empty.
   * <p>Can be overridden in subclasses, e.g. for turning off XML validation
   * or using a different XmlBeanDefinitionParser implementation.
   * @param beanDefinitionReader the bean definition reader used by this context
   * @see org.springframework.beans.factory.xml.XmlBeanDefinitionReader#setValidationMode
   * @see org.springframework.beans.factory.xml.XmlBeanDefinitionReader#setDocumentReaderClass
   */
  protected void initBeanDefinitionReader(XmlBeanDefinitionReader beanDefinitionReader) {
  }

  /**
   * Load the bean definitions with the given XmlBeanDefinitionReader.
   * <p>The lifecycle of the bean factory is handled by the refreshBeanFactory method;
   * therefore this method is just supposed to load and/or register bean definitions.
   * <p>Delegates to a ResourcePatternResolver for resolving location patterns
   * into Resource instances.
   * @throws org.springframework.beans.BeansException in case of bean registration errors
   * @throws java.io.IOException if the required XML document isn't found
   * @see #refreshBeanFactory
   * @see #getConfigLocations
   * @see #getResources
   * @see #getResourcePatternResolver
   */

  //读取配置文件
  protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
    String[] configLocations = getConfigLocations();
    if (configLocations != null) {
      for (int i = 0; i < configLocations.length; i++) {
        reader.loadBeanDefinitions(configLocations[i]);
      }
    }
  }


  /**
   * The default location for the root context is "/WEB-INF/applicationContext.xml",
   * and "/WEB-INF/test-servlet.xml" for a context with the namespace "test-servlet"
   * (like for a DispatcherServlet instance with the servlet-name "test").
   */
  //获得默认的ConfigLocations
  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};
    }
  }

==>AbstractBeanDefinitionReader.loadBeanDefinitions()

public int loadBeanDefinitions(String location) 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 {

//根据配置文件读取相应配置
        Resource[] resources = ((ResourcePatternResolver) resourceLoader).getResources(location);

        int loadCount = loadBeanDefinitions(resources);
        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.
      Resource resource = resourceLoader.getResource(location);
      int loadCount = loadBeanDefinitions(resource);
      if (logger.isDebugEnabled()) {
        logger.debug("Loaded " + loadCount + " bean definitions from location [" + location + "]");
      }
      return loadCount;
    }
  }

这个是其中一个ResourceLoader的实现
==>PathMatchingResourcePatternResolver.getResources(String locationPattern);

 public Resource[] getResources(String locationPattern) throws IOException {
    Assert.notNull(locationPattern, "Location pattern must not be null");
    if (locationPattern.startsWith(CLASSPATH_ALL_URL_PREFIX)) {
      // a class path resource (multiple resources for same name possible)

      if (getPathMatcher().isPattern(locationPattern.substring(CLASSPATH_ALL_URL_PREFIX.length()))) {
        // a class path resource pattern
        return findPathMatchingResources(locationPattern);
      }
      else {
        // all class path resources with the given name
        return findAllClassPathResources(locationPattern.substring(CLASSPATH_ALL_URL_PREFIX.length()));
      }

    }
    else {
      // Only look for a pattern after a prefix here
      // (to not get fooled by a pattern symbol in a strange prefix).
      int prefixEnd = locationPattern.indexOf(":") + 1;
      if (getPathMatcher().isPattern(locationPattern.substring(prefixEnd))) {
        // a file pattern
        return findPathMatchingResources(locationPattern);
      }
      else {
        // a single resource with the given name
        return new Resource[] {getResourceLoader().getResource(locationPattern)};
      }
    }
  }

==>PathMatchingResourcePatternResolver.findPathMatchingResources(String locationPattern);

 protected Resource[] findPathMatchingResources(String locationPattern) throws IOException {
    String rootDirPath = determineRootDir(locationPattern);
    String subPattern = locationPattern.substring(rootDirPath.length());
    Resource[] rootDirResources = getResources(rootDirPath);

//collectionFactory初始化一个set容量为16
    Set result = CollectionFactory.createLinkedSetIfPossible(16);
    for (int i = 0; i < rootDirResources.length; i++) {
      Resource rootDirResource = rootDirResources[i];
      if (isJarResource(rootDirResource)) {
        result.addAll(doFindPathMatchingJarResources(rootDirResource, subPattern));
      }
      else {
        result.addAll(doFindPathMatchingFileResources(rootDirResource, subPattern));
      }
    }

    if (logger.isDebugEnabled()) {
      logger.debug("Resolved location pattern [" + locationPattern + "] to resources " + result);
    }
    return (Resource[]) result.toArray(new Resource[result.size()]);
  }

前面说到有一个刷新WebApplicationContext的操作,但是XmlWebApplicationContext 并没有实现refresh方法,而方法的实现写在

AbstractRefreshableWebApplicationContext 中

==>AbstractRefreshableWebApplicationContext.refresh();
 

public void refresh() throws BeansException {
    if (ObjectUtils.isEmpty(getConfigLocations())) {
      //设置configLocations为默认的getDefaultConfigLocations()
      setConfigLocations(getDefaultConfigLocations());
    }
    super.refresh();
  }

==>AbstractApplicationContext.refresh();

public void refresh() throws BeansException, IllegalStateException {
    synchronized (this.startupShutdownMonitor) {
      this.startupTime = System.currentTimeMillis();

      synchronized (this.activeMonitor) {
        this.active = true;
      }

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

      // Tell the internal bean factory to use the context's class loader.
      beanFactory.setBeanClassLoader(getClassLoader());

      // Populate the bean factory with context-specific resource editors.
      beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this));

      // Configure the bean factory with context semantics.
      beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
      beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
      beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
      beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
      beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);

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

      // Invoke factory processors registered with the context instance.
      for (Iterator it = getBeanFactoryPostProcessors().iterator(); it.hasNext();) {
        BeanFactoryPostProcessor factoryProcessor = (BeanFactoryPostProcessor) it.next();
        factoryProcessor.postProcessBeanFactory(beanFactory);
      }

      if (logger.isInfoEnabled()) {
        if (getBeanDefinitionCount() == 0) {
          logger.info("No beans defined in application context [" + getDisplayName() + "]");
        }
        else {
          logger.info(getBeanDefinitionCount() + " beans defined in application context [" + 

getDisplayName() + "]");
        }
      }

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

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

        // 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 singletons this late to allow them to access the message source.
        beanFactory.preInstantiateSingletons();

        // Last step: publish corresponding event.
        publishEvent(new ContextRefreshedEvent(this));
      }

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

不错，俺的认识又加深了！
就是排版有点问题！
再好好看看！

第一次写东西,请多多指教

原代码大家都会看
最好是写出每一步都做些什么(代码帖得有点多）
从大体上整个结构和思路


不过还不错

大家看源代码习惯怎么看？是广度搜索还是深度搜索？就是遇到其它方法被调用的时候是先看被调用的方法还是继续看完本方法，然后再进入被调用的方法。

以前没什么方法，感性的看，没目的性

现在俺一般是想明白原理，再看源码
应该是再去验证一下是不是和俺想的一样

都是源代码，没法看也没意义。说说原理，理解，需要注意的地方还好点。

<context-param>  
    <param-name>webAppRootKey</param-name>  
    <param-value>task.root</param-value>  
</context-param>  

这段是啥东西？怎么得来的？