深入浅出Spring的IOC容器，对Spring的IOC容器源码进行深入理解

文章目录

1.关于web.xml加载问题

1.1.ServletContext 初始化

1.Tomcat在进行启动的时候，会将context-param等相关参数全部初始化到ServletContext对象上
2.同时，会通知listener-class对应的类ContextLoaderListener(当然，也可以进行自定义)

web.xml 配置样例

<context-param>
   <param-name>name</param-name>
   <param-value>gaoxinfu</param-value>
</context-param>
<listener> 
   <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>

1.2.ContextLoaderListener.contextInitialized(ServletContextEvent)

1.3.ContextLoader.initWebApplicationContext

/**
   * Initialize Spring's web application context for the given servlet context,
   * using the application context provided at construction time, or creating a new one
   * according to the "{@link #CONTEXT_CLASS_PARAM contextClass}" and
   * "{@link #CONFIG_LOCATION_PARAM contextConfigLocation}" context-params.
   * @param servletContext current servlet context
   * @return the new WebApplicationContext
   * @see #ContextLoader(WebApplicationContext)
   * @see #CONTEXT_CLASS_PARAM
   * @see #CONFIG_LOCATION_PARAM
   */
  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!");
    }

    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) {
        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);
        }
      }
      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;
    }
  }

最终实现了下面的赋值

这里进行XMLWebApplicationContext的存储

1.4.servlet的初始化

上面listener的初始化parent context初始化完成之后，会进行初始化各个web.xml文件中的servlet
如下：servlet ：DispatcherServlet的初始化，DispatcherServlet的初始化见下面章节

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:javaee="http://java.sun.com/xml/ns/javaee"
     xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
     xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd"
     version="2.4">
  <display-name>Gupao Web Application</display-name>

  <context-param>
    <param-name>name</param-name>
    <param-value>gaoxinfu</param-value>
  </context-param>
  <listener>
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
  </listener>
  
  <servlet>
    <servlet-name>myservlet</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <init-param>
      <param-name>contextConfigLocation</param-name>
      <param-value>application.properties</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
  </servlet>
  <servlet-mapping>
    <servlet-name>myservlet</servlet-name>
    <url-pattern>/*</url-pattern>
  </servlet-mapping>

</web-app>

1.5.WebApplicationContext的主要实现类

1.5.1.XmlWebApplicationContext

1.采用xml配置，则Spring将使用XmlWebApplicationContext启动Spring容器，即通过XML文件为Spring容器提供Bean的配置信息；

配置样例

<context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>classpath:/config/applicationContext.xml</param-value>
  </context-param>
  <listener>
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
  </listener>

1.5.2.AnnotationConfigWebApplicationContext

如果使用@Configure的java类提供配置信息，则需要在xml中进行相关配置，
设置contextClass参数值为AnnotationConfigWebApplicationContext类，contextConfigLocation参数值则为使用了@Configure注解的类。

使用案例

@Configuration
@ServletComponentScan 
@ImportResource(locations = { "classpath:/config/applicationContext.xml" })
@SpringBootApplication
public class ThirdApplication {

  public static void main(String[] args) {
    System.setProperty("org.apache.cxf.stax.allowInsecureParser","1");
     SpringApplication.run(ThirdApplication.class, args);
  }

1.6.总结

1.这里大家可以认为父parent context:WebApplicationContext的初始化；

首先大家，去看Spring的源码入口，第一个就是DispatcherServlet

2.DispatcherServlet

2.1.整体继承图

2.2.入口:DispatcherServlet.init()

可以看到入口在HttpServletBean.init()中

2.3.HttpServletBean.init()

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

    // Set bean properties from init parameters.
    PropertyValues pvs = new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);
    if (!pvs.isEmpty()) {
      try {
        //定位资源
        BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
        //加载配置信息
        ResourceLoader resourceLoader = new ServletContextResourceLoader(getServletContext());
        bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, getEnvironment()));
        initBeanWrapper(bw);
        bw.setPropertyValues(pvs, true);
      }
      catch (BeansException ex) {
        if (logger.isErrorEnabled()) {
          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");
    }
  }

2.4.FrameworkServlet.initServletBean()