Spring MVC 学习 -- 创建过程

Spring MVC 学习 -- 创建过程

Spring MVC我们使用的时候会在web.xml中配置

   <servlet>
     <servlet-name>SpringMVC</servlet-name>
     <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
     <init-param>
       <param-name>contextConfigLocation</param-name>
       <param-value>classpath:spring/spring-web.xml</param-value>
     </init-param>
   </servlet>
   <servlet-mapping>
     <servlet-name>SpringMVC</servlet-name>
     <url-pattern>/</url-pattern>
   </servlet-mapping>

1.核心的类结构

　　继承结构主要有五个类，GenericServlet和HttpServlet 是Java的，HttpServletBean、FrameworkServlet和DispatcherServlet是Spring MVC的。

　　　　在图中还有三个接口：EnvironmentCapable、EnvironmentAware和ApplicationContextAware~

　　　　XXXAware 在spring里标识对XXX可以感知 -- 白话的意思就是：某个类如果想要使用spring的一些东西，就可以通过实现XXXAware接口告诉spring，spring看到后会给你送过来，而接收的方式是通过实现接口唯一的setXXX

 public interface ApplicationContextAware extends Aware {

 void setApplicationContext(ApplicationContext applicationContext) throws BeansException;

 }

源码如上，使用的话写一个类实现ApplicationContextAware，然后实现setApplicationContext()方法就行，spring为自动调用这个方法将applicationContext传给我们。　

而EnvironmentCapable是为了实现getEnvironment去拿到ServletContext、ServletConfig、JndiProperty、系统环境变量和系统属性。

2.HttpServletBean

     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");
         }
     }

主要看init()方法， 使用了BeanWrapper这个类对象，BeanWrapper是操作JavaBean的工具类，主要就是对属性进行操作。

3.FrameworkServlet

这个类是通过HttpServletBean中的initServletBean()方法进入的。

     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");
         }
     }

核心代码就try里面包含的两句，很显然主要用来初始化WebApplicationContext和初始化FrameworkServlet的。

     protected WebApplicationContext initWebApplicationContext() {
         WebApplicationContext rootContext =
                 WebApplicationContextUtils.getWebApplicationContext(getServletContext());
         WebApplicationContext wac = null;

         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();
         }
         if (wac == null) {
             // No context instance is defined for this servlet -> create a local one
             wac = createWebApplicationContext(rootContext);
         }

         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 + "]");
             }
         }

         return wac;
     }

主要做了三件事：

• 获取spring的根容器rootContext
• 设置webApplicationContext并根据情况调用onRefresh方法
• 将webApplicationContext设置到ServletContext中

4.DispatcherServlet

通过上面onRefresh()方法，调用initStrategies()方法，初始化策略组件。具体的内容就是用来初始化9个组件，每个组件的代码不一一贴出来了， 这几个方法都会去调用getDefaultStrategies()方法。

 protected <T> List<T> getDefaultStrategies(ApplicationContext context, Class<T> strategyInterface) {
         String key = strategyInterface.getName();
         String value = defaultStrategies.getProperty(key);
         if (value != null) {
             String[] classNames = StringUtils.commaDelimitedListToStringArray(value);
             List<T> strategies = new ArrayList<T>(classNames.length);
             for (String className : classNames) {
                 try {
                     Class<?> clazz = ClassUtils.forName(className, DispatcherServlet.class.getClassLoader());
                     Object strategy = createDefaultStrategy(context, clazz);
                     strategies.add((T) strategy);
                 }
                 catch (ClassNotFoundException ex) {
                     throw new BeanInitializationException(
                             "Could not find DispatcherServlet's default strategy class [" + className +
                                     "] for interface [" + key + "]", ex);
                 }
                 catch (LinkageError err) {
                     throw new BeanInitializationException(
                             "Error loading DispatcherServlet's default strategy class [" + className +
                                     "] for interface [" + key + "]: problem with class file or dependent class", err);
                 }
             }
             return strategies;
         }
         else {
             return new LinkedList<T>();
         }
     }

5.代码测试

配置内容都不再贴了，启动Tomcat，然后去请求某个controller地址，进入HttpServletBean的init()方法

然后继续，因为WebApplicationContext是null，会进入

然后configureAndRefreshWebApplicationContext方法中会执行refresh()，这部分可以看spring bean加载过程和实例化。