Spring源码分析之与WEB服务器衔接（下）

SpringMVC子容器的启动，也就是DispatcherServlet的初始化，它的父类HttpServletBean实现了servlet的初始化方法

public final void init() throws ServletException {
  if (logger.isDebugEnabled()) {
    logger.debug("Initializing servlet '" + getServletName() + "'");
  }

  // Set bean properties from init parameters.
  try {
    PropertyValues pvs = new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);
    BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
    ResourceLoader resourceLoader = new ServletContextResourceLoader(getServletContext());
    bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, getEnvironment()));
    initBeanWrapper(bw);
    bw.setPropertyValues(pvs, true);
  }
  catch (BeansException ex) {
    logger.error("Failed to set bean properties on servlet '" + getServletName() + "'", ex);
    throw ex;
  }

  // Let subclasses do whatever initialization they like.
  initServletBean();

  if (logger.isDebugEnabled()) {
    logger.debug("Servlet '" + getServletName() + "' configured successfully");
  }
}

获取配置文件配置的servlet初始配置，并设置到对应servlet的属性上，例如容器上下的配置文件路径

public ServletConfigPropertyValues(ServletConfig config, Set<String> requiredProperties)
      throws ServletException {

  Set<String> missingProps = (requiredProperties != null && !requiredProperties.isEmpty()) ?
      new HashSet<String>(requiredProperties) : null;

  Enumeration<String> en = config.getInitParameterNames();
  while (en.hasMoreElements()) {
    String property = en.nextElement();
    Object value = config.getInitParameter(property);
    addPropertyValue(new PropertyValue(property, value));
    if (missingProps != null) {
      missingProps.remove(property);
    }
  }

  // Fail if we are still missing properties.
  if (missingProps != null && missingProps.size() > 0) {
    throw new ServletException(
      "Initialization from ServletConfig for servlet '" + config.getServletName() +
      "' failed; the following required properties were missing: " +
      StringUtils.collectionToDelimitedString(missingProps, ", "));
  }
}

初始化servlet类

protected final void initServletBean() throws ServletException {
  getServletContext().log("Initializing Spring FrameworkServlet '" + getServletName() + "'");
  if (this.logger.isInfoEnabled()) {
    this.logger.info("FrameworkServlet '" + getServletName() + "': initialization started");
  }
  long startTime = System.currentTimeMillis();

  try {
    this.webApplicationContext = initWebApplicationContext();
    initFrameworkServlet();
  }
  catch (ServletException ex) {
    this.logger.error("Context initialization failed", ex);
    throw ex;
  }
  catch (RuntimeException ex) {
    this.logger.error("Context initialization failed", ex);
    throw ex;
  }

  if (this.logger.isInfoEnabled()) {
    long elapsedTime = System.currentTimeMillis() - startTime;
    this.logger.info("FrameworkServlet '" + getServletName() + "': initialization completed in " +
        elapsedTime + " ms");
  }
}

初始化web上下文容器，首先从servlet上下文中获取父容器

public static WebApplicationContext getWebApplicationContext(ServletContext sc) {
  return getWebApplicationContext(sc, WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE);
}

判断servlet的web容器是否存在

if (this.webApplicationContext != null) {
  // A context instance was injected at construction time -> use it
  wac = this.webApplicationContext;
  if (wac instanceof ConfigurableWebApplicationContext) {
    ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac;
    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 -> set
        // the root application context (if any; may be null) as the parent
        cwac.setParent(rootContext);
      }
      configureAndRefreshWebApplicationContext(cwac);
    }
  }
}
if (wac == null) {
  // No context instance was injected at construction time -> see if one
  // has been registered in the servlet context. If one exists, it is assumed
  // that the parent context (if any) has already been set and that the
  // user has performed any initialization such as setting the context id
  wac = findWebApplicationContext();
}

没有的话从servlet上下文中查找

protected WebApplicationContext findWebApplicationContext() {
  String attrName = getContextAttribute();
  if (attrName == null) {
    return null;
  }
  WebApplicationContext wac =
      WebApplicationContextUtils.getWebApplicationContext(getServletContext(), attrName);
  if (wac == null) {
    throw new IllegalStateException("No WebApplicationContext found: initializer not registered?");
  }
  return wac;
}

最后创建新的web上下文

protected WebApplicationContext createWebApplicationContext(WebApplicationContext parent) {
  return createWebApplicationContext((ApplicationContext) parent);
}

获取上下文类型，默认为XmlWebApplicationContext

private Class<?> contextClass = DEFAULT_CONTEXT_CLASS;
public Class<?> getContextClass() {
  return this.contextClass;
}

初始化上下文环境，设置父容器，设置配置路径

protected WebApplicationContext createWebApplicationContext(ApplicationContext parent) {
  Class<?> contextClass = getContextClass();
  if (this.logger.isDebugEnabled()) {
    this.logger.debug("Servlet with name '" + getServletName() +
        "' will try to create custom WebApplicationContext context of class '" +
        contextClass.getName() + "'" + ", using parent context [" + parent + "]");
  }
  if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) {
    throw new ApplicationContextException(
        "Fatal initialization error in servlet with name '" + getServletName() +
        "': custom WebApplicationContext class [" + contextClass.getName() +
        "] is not of type ConfigurableWebApplicationContext");
  }
  ConfigurableWebApplicationContext wac =
      (ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);

  wac.setEnvironment(getEnvironment());
  wac.setParent(parent);
  wac.setConfigLocation(getContextConfigLocation());

  configureAndRefreshWebApplicationContext(wac);

  return wac;
}

配置id，servlet上下文配置，命名空间，添加上下文监听器，执行后置处理以及设置的上下文全局初始化器的初始化，最后启动上下文。

protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac) {
  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
    if (this.contextId != null) {
      wac.setId(this.contextId);
    }
    else {
      // Generate default id...
      wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +
          ObjectUtils.getDisplayString(getServletContext().getContextPath()) + "/" + getServletName());
    }
  }

  wac.setServletContext(getServletContext());
  wac.setServletConfig(getServletConfig());
  wac.setNamespace(getNamespace());
  wac.addApplicationListener(new SourceFilteringListener(wac, new ContextRefreshListener()));

  // 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(getServletContext(), getServletConfig());
  }

  postProcessWebApplicationContext(wac);
  applyInitializers(wac);
  wac.refresh();
}

当web容器启动完成后，发送刷新事件，设置接收标志

private class ContextRefreshListener implements ApplicationListener<ContextRefreshedEvent> {

  @Override
  public void onApplicationEvent(ContextRefreshedEvent event) {
    FrameworkServlet.this.onApplicationEvent(event);
  }
}

public void onApplicationEvent(ContextRefreshedEvent event) {
  this.refreshEventReceived = true;
  onRefresh(event.getApplicationContext());
}

判断是否收到web上下文初始化完成事件，往servlet上下文中添加该servlet对应的上下文信息

if (!this.refreshEventReceived) {
  // Either the context is not a ConfigurableApplicationContext with refresh
  // support or the context injected at construction time had already been
  // refreshed -> trigger initial onRefresh manually here.
  onRefresh(wac);
}

if (this.publishContext) {
  // Publish the context as a servlet context attribute.
  String attrName = getServletContextAttributeName();
  getServletContext().setAttribute(attrName, wac);
  if (this.logger.isDebugEnabled()) {
    this.logger.debug("Published WebApplicationContext of servlet '" + getServletName() +
        "' as ServletContext attribute with name [" + attrName + "]");
  }
}