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HttpServletBean 、 FrameworkServlet 和 DispatcherServlet 关系

DispatcherServlet初始化顺序

继承体系结构如下所示:

dispatcherServlet 继承FrameworkServlet 继承 HttpServletBean 继承 HttpServlet

HttpServletBean继承HttpServlet因此在Web容器启动时将调用它的init方法,该初始化方法的主要作用:

将Servlet初始化参数(init-param)设置到该组件上(如contextAttribute、contextClass、namespace、contextConfigLocation),通过BeanWrapper简化设值过程,方便后续使用;

提供给子类初始化扩展点,initServletBean(),该方法由FrameworkServlet覆盖。

 1   <!-- This servlet must be loaded first to configure the log4j
 2      system and create the WebApplicationContext
 3      -->
 4     <servlet>
 5         <servlet-name>config</servlet-name>
 6         <servlet-class>org.springframework.framework.web.context.ContextLoaderServlet</servlet-class>
 7         <init-param>
 8             <param-name>contextClass</param-name>
 9             <param-value>org.springframework.framework.web.context.XMLWebApplicationContext</param-value>           
10         </init-param>    
11         <init-param>
12             <param-name>log4jPropertiesUrl</param-name>
13             <param-value>/WEB-INF/log4j_PRODUCTION.properties</param-value>           
14         </init-param>    
15         <!-- This is essential -->
16         <load-on-startup>1</load-on-startup>
17       </servlet>

 

 1 public abstract class HttpServletBean extends HttpServlet implements EnvironmentAware{  
 2 @Override  
 3     public final void init() throws ServletException {  
 4        //省略部分代码  
 5        //1、如下代码的作用是将Servlet初始化参数设置到该组件上  
 6     //如contextAttribute、contextClass、namespace、contextConfigLocation;  
 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, this.environment));  
12            initBeanWrapper(bw);  
13            bw.setPropertyValues(pvs, true);  
14        }  
15        catch (BeansException ex) {  
16            //…………省略其他代码  
17        }  
18        //2、提供给子类初始化的扩展点,该方法由FrameworkServlet覆盖  
19        initServletBean();  
20        if (logger.isDebugEnabled()) {  
21            logger.debug("Servlet ‘" + getServletName() + "‘ configured successfully");  
22        }  
23     }  
24     //…………省略其他代码  
25 }  

2、FrameworkServlet继承HttpServletBean通过initServletBean()进行Web上下文初始化,该方法主要覆盖一下两件事情:

    初始化web上下文;

    提供给子类初始化扩展点;

 1 public abstract class FrameworkServlet extends HttpServletBean {  
 2 @Override  
 3     protected final void initServletBean() throws ServletException {  
 4         //省略部分代码  
 5        try {  
 6              //1、初始化Web上下文  
 7            this.webApplicationContext = initWebApplicationContext();  
 8              //2、提供给子类初始化的扩展点  
 9            initFrameworkServlet();  
10        }  
11         //省略部分代码  
12     }  
13 }  
 1 protected WebApplicationContext initWebApplicationContext() {  
 2         //ROOT上下文(ContextLoaderListener加载的)  
 3        WebApplicationContext rootContext =  
 4               WebApplicationContextUtils.getWebApplicationContext(getServletContext());  
 5        WebApplicationContext wac = null;  
 6        if (this.webApplicationContext != null) {  
 7            // 1、在创建该Servlet注入的上下文  
 8            wac = this.webApplicationContext;  
 9            if (wac instanceof ConfigurableWebApplicationContext) {  
10               ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac;  
11               if (!cwac.isActive()) {  
12                   if (cwac.getParent() == null) {  
13                       cwac.setParent(rootContext);  
14                   }  
15                   configureAndRefreshWebApplicationContext(cwac);  
16               }  
17            }  
18        }  
19        if (wac == null) {  
20              //2、查找已经绑定的上下文  
21            wac = findWebApplicationContext();  
22        }  
23        if (wac == null) {  
24             //3、如果没有找到相应的上下文,并指定父亲为ContextLoaderListener  
25            wac = createWebApplicationContext(rootContext);  
26        }  
27        if (!this.refreshEventReceived) {  
28              //4、刷新上下文(执行一些初始化)  
29            onRefresh(wac);  
30        }  
31        if (this.publishContext) {  
32            // Publish the context as a servlet context attribute.  
33            String attrName = getServletContextAttributeName();  
34            getServletContext().setAttribute(attrName, wac);  
35            //省略部分代码  
36        }  
37        return wac;  
38     }  

从initWebApplicationContext()方法可以看出,基本上如果ContextLoaderListener加载了上下文将作为根上下文(DispatcherServlet的父容器)。 

最后调用了onRefresh()方法执行容器的一些初始化,这个方法由子类实现,来进行扩展。

3、DispatcherServlet继承FrameworkServlet,并实现了onRefresh()方法提供一些前端控制器相关的配置:

 1 public class DispatcherServlet extends FrameworkServlet {  
 2      //实现子类的onRefresh()方法,该方法委托为initStrategies()方法。  
 3     @Override  
 4     protected void onRefresh(ApplicationContext context) {  
 5        initStrategies(context);  
 6     }  
 7    
 8     //初始化默认的Spring Web MVC框架使用的策略(如HandlerMapping)  
 9     protected void initStrategies(ApplicationContext context) {  
10        initMultipartResolver(context);  
11        initLocaleResolver(context);  
12        initThemeResolver(context);  
13        initHandlerMappings(context);  
14        initHandlerAdapters(context);  
15        initHandlerExceptionResolvers(context);  
16        initRequestToViewNameTranslator(context);  
17        initViewResolvers(context);  
18        initFlashMapManager(context);  
19     }  
20 }  

从如上代码可以看出,DispatcherServlet启动时会进行我们需要的Web层Bean的配置,如HandlerMapping、HandlerAdapter等,而且如果我们没有配置,还会给我们提供默认的配置。

 

从如上代码我们可以看出,整个DispatcherServlet初始化的过程和做了些什么事情,具体主要做了如下两件事情:

1、初始化Spring Web MVC使用的Web上下文,并且可能指定父容器为(ContextLoaderListener加载了根上下文);

2、初始化DispatcherServlet使用的策略,如HandlerMapping、HandlerAdapter等。 

 

服务器启动时的日志分析(此处加上了ContextLoaderListener从而启动ROOT上下文容器): 

 信息: Initializing Spring root WebApplicationContext //ContextLoaderListener启动ROOT上下文

 

2012-03-12 13:33:55 [main] INFO  org.springframework.web.context.ContextLoader - Root WebApplicationContext: initialization started

2012-03-12 13:33:55 [main] INFO  org.springframework.web.context.support.XmlWebApplicationContext - Refreshing Root WebApplicationContext: startup date [Mon Mar 12 13:33:55 CST 2012]; root of context hierarchy

2012-03-12 13:33:55 [main] DEBUG org.springframework.beans.factory.xml.DefaultBeanDefinitionDocumentReader - Loading bean definitions

2012-03-12 13:33:55 [main] DEBUG org.springframework.beans.factory.xml.XmlBeanDefinitionReader - Loaded 0 bean definitions from location pattern [/WEB-INF/ContextLoaderListener.xml]

2012-03-12 13:33:55 [main] DEBUG org.springframework.web.context.support.XmlWebApplicationContext - Bean factory for Root WebApplicationContext: org.springframework.beans.factory.support.DefaultListableBeanFactory@1c05ffd: defining beans []; root of factory hierarchy

2012-03-12 13:33:55 [main] DEBUG org.springframework.web.context.support.XmlWebApplicationContext - Bean factory for Root WebApplicationContext:

2012-03-12 13:33:55 [main] DEBUG org.springframework.web.context.ContextLoader - Published root WebApplicationContext as ServletContext attribute with name [org.springframework.web.context.WebApplicationContext.ROOT] //ROOT上下文绑定到ServletContext

2012-03-12 13:33:55 [main] INFO  org.springframework.web.context.ContextLoader - Root WebApplicationContext: initialization completed in 438 ms  //到此ROOT上下文启动完毕

 

 2012-03-12 13:33:55 [main] DEBUG org.springframework.web.servlet.DispatcherServlet - Initializing servlet ‘chapter2‘

信息: Initializing Spring FrameworkServlet ‘chapter2‘  //开始初始化FrameworkServlet对应的Web上下文

2012-03-12 13:33:55 [main] INFO  org.springframework.web.servlet.DispatcherServlet - FrameworkServlet ‘chapter2‘: initialization started

2012-03-12 13:33:55 [main] DEBUG org.springframework.web.servlet.DispatcherServlet - Servlet with name ‘chapter2‘ will try to create custom WebApplicationContext context of class ‘org.springframework.web.context.support.XmlWebApplicationContext‘, using parent context [Root WebApplicationContext: startup date [Mon Mar 12 13:33:55 CST 2012]; root of context hierarchy]

//此处使用Root WebApplicationContext作为父容器。

2012-03-12 13:33:55 [main] INFO  org.springframework.web.context.support.XmlWebApplicationContext - Refreshing WebApplicationContext for namespace ‘chapter2-servlet‘: startup date [Mon Mar 12 13:33:55 CST 2012]; parent: Root WebApplicationContext

2012-03-12 13:33:55 [main] INFO  org.springframework.beans.factory.xml.XmlBeanDefinitionReader - Loading XML bean definitions from ServletContext resource [/WEB-INF/chapter2-servlet.xml]

2012-03-12 13:33:55 [main] DEBUG org.springframework.beans.factory.xml.DefaultBeanDefinitionDocumentReader - Loading bean definitions

2012-03-12 13:33:55 [main] DEBUG org.springframework.beans.factory.xml.BeanDefinitionParserDelegate - Neither XML ‘id‘ nor ‘name‘ specified - using generated bean name[org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping#0]  //我们配置的HandlerMapping

2012-03-12 13:33:55 [main] DEBUG org.springframework.beans.factory.xml.BeanDefinitionParserDelegate - Neither XML ‘id‘ nor ‘name‘ specified - using generated bean name[org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter#0] //我们配置的HandlerAdapter

2012-03-12 13:33:55 [main] DEBUG org.springframework.beans.factory.xml.BeanDefinitionParserDelegate - Neither XML ‘id‘ nor ‘name‘ specified - using generated bean name [org.springframework.web.servlet.view.InternalResourceViewResolver#0] //我们配置的ViewResolver

2012-03-12 13:33:55 [main] DEBUG org.springframework.beans.factory.xml.BeanDefinitionParserDelegate - No XML ‘id‘ specified - using ‘/hello‘ as bean name and [] as aliases 

//我们的处理器(HelloWorldController

2012-03-12 13:33:55 [main] DEBUG org.springframework.beans.factory.xml.XmlBeanDefinitionReader - Loaded 4 bean definitions from location pattern [/WEB-INF/chapter2-servlet.xml]

2012-03-12 13:33:55 [main] DEBUG org.springframework.web.context.support.XmlWebApplicationContext - Bean factory for WebApplicationContext for namespace ‘chapter2-servlet‘: org.springframework.beans.factory.support.DefaultListableBeanFactory@1372656: defining beans [org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping#0,org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter#0,org.springframework.web.servlet.view.InternalResourceViewResolver#0,/hello]; parent: org.springframework.beans.factory.support.DefaultListableBeanFactory@1c05ffd

//到此容器注册的Bean初始化完毕

 

2012-03-12 13:33:56 [main] DEBUG org.springframework.web.servlet.DispatcherServlet - Unable to locate MultipartResolver with name ‘multipartResolver‘: no multipart request handling provided

 

2012-03-12 13:33:56 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating instance of bean ‘org.springframework.web.servlet.i18n.AcceptHeaderLocaleResolver‘

//默认的LocaleResolver注册

2012-03-12 13:33:56 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating instance of bean ‘org.springframework.web.servlet.theme.FixedThemeResolver‘

//默认的ThemeResolver注册

 

2012-03-12 13:33:56 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Returning cached instance of singleton bean ‘org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping#0‘

//发现我们定义的HandlerMapping 不再使用默认的HandlerMapping

 

2012-03-12 13:33:56 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Returning cached instance of singleton bean ‘org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter#0‘

//发现我们定义的HandlerAdapter 不再使用默认的HandlerAdapter

 

2012-03-12 13:33:56 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating instance of bean ‘org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerExceptionResolver‘

//异常处理解析器ExceptionResolver

2012-03-12 13:33:56 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating instance of bean ‘org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerExceptionResolver‘

 

2012-03-12 13:33:56 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Returning cached instance of singleton bean ‘org.springframework.web.servlet.view.InternalResourceViewResolver#0‘

 

2012-03-12 13:33:56 [main] DEBUG org.springframework.web.servlet.DispatcherServlet - Published WebApplicationContext of servlet ‘chapter2‘ as ServletContext attribute with name [org.springframework.web.servlet.FrameworkServlet.CONTEXT.chapter2]

//绑定FrameworkServlet初始化的Web上下文到ServletContext

2012-03-12 13:33:56 [main] INFO  org.springframework.web.servlet.DispatcherServlet - FrameworkServlet ‘chapter2‘: initialization completed in  297 ms

2012-03-12 13:33:56 [main] DEBUG org.springframework.web.servlet.DispatcherServlet - Servlet ‘chapter2‘ configured successfully

//到此完整流程结束 

  

从如上日志我们也可以看出,DispatcherServlet会进行一些默认的配置。接下来我们看一下默认配置吧。

 

3.5、DispatcherServlet默认配置

DispatcherServlet的默认配置在DispatcherServlet.properties(和DispatcherServlet类在一个包下)中,而且是当Spring配置文件中没有指定配置时使用的默认策略:

org.springframework.web.servlet.LocaleResolver=org.springframework.web.servlet.i18n.AcceptHeaderLocaleResolver  
  
org.springframework.web.servlet.ThemeResolver=org.springframework.web.servlet.theme.FixedThemeResolver  
  
org.springframework.web.servlet.HandlerMapping=org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping,\  
    org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMapping  
  
org.springframework.web.servlet.HandlerAdapter=org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter,\  
    org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter,\  
    org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter  
  
org.springframework.web.servlet.HandlerExceptionResolver=org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerExceptionResolver,\  
    org.springframework.web.servlet.mvc.annotation.ResponseStatusExceptionResolver,\  
    org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver  
  
org.springframework.web.servlet.RequestToViewNameTranslator=org.springframework.web.servlet.view.DefaultRequestToViewNameTranslator  
  
org.springframework.web.servlet.ViewResolver=org.springframework.web.servlet.view.InternalResourceViewResolver  
  
org.springframework.web.servlet.FlashMapManager=org.springframework.web.servlet.support.SessionFlashMapManager  

从如上配置可以看出DispatcherServlet在启动时会自动注册这些特殊的Bean,无需我们注册,如果我们注册了,默认的将不会注册。 

因此如第二章的BeanNameUrlHandlerMapping、SimpleControllerHandlerAdapter是不需要注册的,DispatcherServlet默认会注册这两个Bean。

 

从DispatcherServlet.properties可以看出有许多特殊的Bean,那接下来我们就看看Spring Web MVC主要有哪些特殊的Bean。

3.6、DispatcherServlet中使用的特殊的Bean

DispatcherServlet默认使用WebApplicationContext作为上下文,因此我们来看一下该上下文中有哪些特殊的Bean:

1、Controller处理器/页面控制器,做的是MVC中的C的事情,但控制逻辑转移到前端控制器了,用于对请求进行处理;

2、HandlerMapping请求到处理器的映射,如果映射成功返回一个HandlerExecutionChain对象(包含一个Handler处理器(页面控制器)对象、多个HandlerInterceptor拦截器)对象;如BeanNameUrlHandlerMapping将URL与Bean名字映射,映射成功的Bean就是此处的处理器;

3、HandlerAdapterHandlerAdapter将会把处理器包装为适配器,从而支持多种类型的处理器,即适配器设计模式的应用,从而很容易支持很多类型的处理器;如SimpleControllerHandlerAdapter将对实现了Controller接口的Bean进行适配,并且掉处理器的handleRequest方法进行功能处理;

4、ViewResolverViewResolver将把逻辑视图名解析为具体的View,通过这种策略模式,很容易更换其他视图技术;如InternalResourceViewResolver将逻辑视图名映射为jsp视图;

5、LocalResover本地化解析,因为Spring支持国际化,因此LocalResover解析客户端的Locale信息从而方便进行国际化;

6、ThemeResovler主题解析,通过它来实现一个页面多套风格,即常见的类似于软件皮肤效果;

7、MultipartResolver文件上传解析,用于支持文件上传;

8HandlerExceptionResolver处理器异常解析,可以将异常映射到相应的统一错误界面,从而显示用户友好的界面(而不是给用户看到具体的错误信息);

9RequestToViewNameTranslator当处理器没有返回逻辑视图名等相关信息时,自动将请求URL映射为逻辑视图名;

10FlashMapManager用于管理FlashMap的策略接口,FlashMap用于存储一个请求的输出,当进入另一个请求时作为该请求的输入,通常用于重定向场景,后边会细述。

HttpServletBean 、 FrameworkServlet 和 DispatcherServlet 关系