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

 1   <servlet>
 2     <servlet-name>SpringMVC</servlet-name>
 3     <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
 4     <init-param>
 5       <param-name>contextConfigLocation</param-name>
 6       <param-value>classpath:spring/spring-web.xml</param-value>
 7     </init-param>
 8   </servlet>
 9   <servlet-mapping>
10     <servlet-name>SpringMVC</servlet-name>
11     <url-pattern>/</url-pattern>
12   </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

1 public interface ApplicationContextAware extends Aware {
2     
3 void setApplicationContext(ApplicationContext applicationContext) throws BeansException;
4 
5 }

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

 1     public final void init() throws ServletException {
 2         if (logger.isDebugEnabled()) {
 3             logger.debug("Initializing servlet '" + getServletName() + "'");
 4         }
 5 
 6         // Set bean properties from init parameters.
 7         try {
 8             PropertyValues pvs = new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);
 9             BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
10             ResourceLoader resourceLoader = new ServletContextResourceLoader(getServletContext());
11             bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, getEnvironment()));
12             initBeanWrapper(bw);
13             bw.setPropertyValues(pvs, true);
14         }
15         catch (BeansException ex) {
16             logger.error("Failed to set bean properties on servlet '" + getServletName() + "'", ex);
17             throw ex;
18         }
19 
20         // Let subclasses do whatever initialization they like.
21         initServletBean();
22 
23         if (logger.isDebugEnabled()) {
24             logger.debug("Servlet '" + getServletName() + "' configured successfully");
25         }
26     }

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。

 1     protected final void initServletBean() throws ServletException {
 2         getServletContext().log("Initializing Spring FrameworkServlet '" + getServletName() + "'");
 3         if (this.logger.isInfoEnabled()) {
 4             this.logger.info("FrameworkServlet '" + getServletName() + "': initialization started");
 5         }
 6         long startTime = System.currentTimeMillis();
 7 
 8         try {
 9             this.webApplicationContext = initWebApplicationContext();
10             initFrameworkServlet();
11         }
12         catch (ServletException ex) {
13             this.logger.error("Context initialization failed", ex);
14             throw ex;
15         }
16         catch (RuntimeException ex) {
17             this.logger.error("Context initialization failed", ex);
18             throw ex;
19         }
20 
21         if (this.logger.isInfoEnabled()) {
22             long elapsedTime = System.currentTimeMillis() - startTime;
23             this.logger.info("FrameworkServlet '" + getServletName() + "': initialization completed in " +
24                     elapsedTime + " ms");
25         }
26     }

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。

 1     protected WebApplicationContext initWebApplicationContext() {
 2         WebApplicationContext rootContext =
 3                 WebApplicationContextUtils.getWebApplicationContext(getServletContext());
 4         WebApplicationContext wac = null;
 5 
 6         if (this.webApplicationContext != null) {
 7             // A context instance was injected at construction time -> use it
 8             wac = this.webApplicationContext;
 9             if (wac instanceof ConfigurableWebApplicationContext) {
10                 ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac;
11                 if (!cwac.isActive()) {
12                     // The context has not yet been refreshed -> provide services such as
13                     // setting the parent context, setting the application context id, etc
14                     if (cwac.getParent() == null) {
15                         // The context instance was injected without an explicit parent -> set
16                         // the root application context (if any; may be null) as the parent
17                         cwac.setParent(rootContext);
18                     }
19                     configureAndRefreshWebApplicationContext(cwac);
20                 }
21             }
22         }
23         if (wac == null) {
24             // No context instance was injected at construction time -> see if one
25             // has been registered in the servlet context. If one exists, it is assumed
26             // that the parent context (if any) has already been set and that the
27             // user has performed any initialization such as setting the context id
28             wac = findWebApplicationContext();
29         }
30         if (wac == null) {
31             // No context instance is defined for this servlet -> create a local one
32             wac = createWebApplicationContext(rootContext);
33         }
34 
35         if (!this.refreshEventReceived) {
36             // Either the context is not a ConfigurableApplicationContext with refresh
37             // support or the context injected at construction time had already been
38             // refreshed -> trigger initial onRefresh manually here.
39             onRefresh(wac);
40         }
41 
42         if (this.publishContext) {
43             // Publish the context as a servlet context attribute.
44             String attrName = getServletContextAttributeName();
45             getServletContext().setAttribute(attrName, wac);
46             if (this.logger.isDebugEnabled()) {
47                 this.logger.debug("Published WebApplicationContext of servlet '" + getServletName() +
48                         "' as ServletContext attribute with name [" + attrName + "]");
49             }
50         }
51 
52         return wac;
53     }

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。

 1 protected <T> List<T> getDefaultStrategies(ApplicationContext context, Class<T> strategyInterface) {
 2         String key = strategyInterface.getName();
 3         String value = defaultStrategies.getProperty(key);
 4         if (value != null) {
 5             String[] classNames = StringUtils.commaDelimitedListToStringArray(value);
 6             List<T> strategies = new ArrayList<T>(classNames.length);
 7             for (String className : classNames) {
 8                 try {
 9                     Class<?> clazz = ClassUtils.forName(className, DispatcherServlet.class.getClassLoader());
10                     Object strategy = createDefaultStrategy(context, clazz);
11                     strategies.add((T) strategy);
12                 }
13                 catch (ClassNotFoundException ex) {
14                     throw new BeanInitializationException(
15                             "Could not find DispatcherServlet's default strategy class [" + className +
16                                     "] for interface [" + key + "]", ex);
17                 }
18                 catch (LinkageError err) {
19                     throw new BeanInitializationException(
20                             "Error loading DispatcherServlet's default strategy class [" + className +
21                                     "] for interface [" + key + "]: problem with class file or dependent class", err);
22                 }
23             }
24             return strategies;
25         }
26         else {
27             return new LinkedList<T>();
28         }
29     }

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。