springmvc之初始化

1.核心接口

dispatchServlet UML图:

DispatchServlet,httpservletBean,FrameWorkServlet这三个类直接实现了EnvironmentCapable,EnvironmentAware以及ApplicationContextAware接口.

科普:

①:XXXAwaare在spring里表示对XXX感知,也就是:如果在某个类里面想要使用spring的一些东西,就可以通过实现XXXAware接口告诉spring,spring看到后就会给你送过来,而接收的方式是通过实现接口唯一的方法setXXX().比如:有个类想要使用当前的applicationContext,我们只需要让他实现ApplicationContextAware接口,然后实现接口中唯一的方法,void setApplicationContext(ApplicationContext applicaitonContext)就可以了,spring会自动调用这个方法将applicationContext传过来.

②:XXXCapable在spring中就是具有XXX的能力,比如:EnvironmentCapable就是告诉spring,他有提供Environment的能力,EnvironmentCapable唯一的方法及时Environment getEnvironment()当;spring需要Environment时,就会调用其get方法跟他要.

springmvc启动

httpServletBean

DispatchServlet创建时,可以直接调用无参的init方法,dispatchServlet默认调用httpServletbean的init方法,如下:(篇幅有点长,省略try…catch)

 public final void init() throws ServletException {
 		//将servlet中配置的参数封装到pvs中,requireProperties为必须参数,没有将抛出ServletException
        PropertyValues pvs = new HttpServletBean.ServletConfigPropertyValues(this.getServletConfig(), this.requiredProperties);
        if (!pvs.isEmpty()) {
                BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
                ResourceLoader resourceLoader = new ServletContextResourceLoader(this.getServletContext());
                bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, this.getEnvironment()));
                //模板方法,可以在子类中调用,做一些初始化工作(默认空实现).这里的bw代表Dispatchservlet;
                this.initBeanWrapper(bw);
                //通过beanWrapper将配置的初始化值(如:contextConfigLocation属性)设置到dispatchServlet中;
                bw.setPropertyValues(pvs, true);
        //模板方法,子类初始化的方法入口.这里做个空实现,具体实现在FrameWorkServlet中.
        this.initServletBean();
        if (this.logger.isDebugEnabled()) {
            this.logger.debug("Servlet '" + this.getServletName() + "' configured successfully");
        }
    }

FrameWorkServlet

从httpServletBean中可知,FrameworkServlet的初始化入口方法是initservletBean().方法代码如下:

//去除try..catch以及日志打印代码,其核心只做了两件事情
 protected final void initServletBean() throws ServletException {
 			// 1.初始化WebApplcationContext(ConfigurableWebApplicationContext)
            this.webApplicationContext = this.initWebApplicationContext();
            // 2.初始化FrameworkServlet,次方式为模板方法,空实现,子类Dispatchservlet并没有使用它
            this.initFrameworkServlet();
 }

可见frameworkservlet在构建过程中的主要作用就是初始化WebApplicationContext,下面为initWebApplicationContext代码:

 protected WebApplicationContext initWebApplicationContext() {
 		//获取rootContext
        WebApplicationContext rootContext = WebApplicationContextUtils.getWebApplicationContext(this.getServletContext());
        WebApplicationContext wac = null;
        //如果已经通过构造方法设置了WebApplicationContext
        if (this.webApplicationContext != null) {
            wac = this.webApplicationContext;
            if (wac instanceof ConfigurableWebApplicationContext) {
                ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext)wac;
                if (!cwac.isActive()) {
                    if (cwac.getParent() == null) {
                        cwac.setParent(rootContext);
                    }
                    this.configureAndRefreshWebApplicationContext(cwac);
                }
            }
        }
        if (wac == null) {
        	//当webApplicationContext已经存在于servletContext中,通过配置在servlet中的contextAttribute获取
            wac = this.findWebApplicationContext();
        }
        if (wac == null) {
        	//如果webApplicationContext还没有,则创建一个,一般情况都是调用 这个创建.
            wac = this.createWebApplicationContext(rootContext);
        }
        if (!this.refreshEventReceived) {
        	//模板方法,当ContextRefreshedEvent事件没有触发时调用此方法,在子类dispatchServlet中具体实现.
            this.onRefresh(wac);
        }
        if (this.publishContext) {
        	//将ApplicationContext设置到servletContext中,
            String attrName = this.getServletContextAttributeName();
            this.getServletContext().setAttribute(attrName, wac);
        }
        return wac;
    }

主要分析一下createWebApplicationContext(rootContext) 方法,贴代码:

protected WebApplicationContext createWebApplicationContext(ApplicationContext parent) {
		//获取创建类型
        Class<?> contextClass = this.getContextClass();
     	//检查创建类型( A.class.isAssignableFrom(B.class):判断A是不是B的超类) contextclass 默认为XmlWebApplicationContext
        if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) {
            throw new ApplicationContextException("Fatal initialization error in servlet with name '" + this.getServletName() + "': custom WebApplicationContext class [" + contextClass.getName() + "] is not of type ConfigurableWebApplicationContext");
        } else {
			//默认会走这里
            ConfigurableWebApplicationContext wac = (ConfigurableWebApplicationContext)BeanUtils.instantiateClass(contextClass);
            wac.setEnvironment(this.getEnvironment());
            wac.setParent(parent);
            //将设置的contextConfigLocaltion传递给wac
            wac.setConfigLocation(this.getContextConfigLocation());
			//这里面添加了应用 监听器,ContextRefreshListener
            this.configureAndRefreshWebApplicationContext(wac);
            return wac;
        }
    }

ContextRefreshListener是FrameWorkServlet的内部类

private class ContextRefreshListener implements ApplicationListener<ContextRefreshedEvent> {
		@Override
		public void onApplicationEvent(ContextRefreshedEvent event) {
			FrameworkServlet.this.onApplicationEvent(event);
		}
}
	public void onApplicationEvent(ContextRefreshedEvent event) {
		this.refreshEventReceived = true;
		//模板方法,在子类dispatchservlet中具体实现
		onRefresh(event.getApplicationContext());
	}

DispatchServlet

onRefresh 方法是Dispatchservlet的入口方法,onrefresh中调用了initStrategies,在initstrategies中调用了9个方法.

//org.springframework.web.servlet.DispatcherServlet
protected void onRefresh(ApplicationContext context) {
		initStrategies(context);
}

//熟悉的味道
protected void initStrategies(ApplicationContext context) {
		initMultipartResolver(context);
		initLocaleResolver(context);
		initThemeResolver(context);
		initHandlerMappings(context);
		initHandlerAdapters(context);
		initHandlerExceptionResolvers(context);
		initRequestToViewNameTranslator(context);
		initViewResolvers(context);
		initFlashMapManager(context);
}

这里9个初始化方法都类似,这里以初始化handlerMapping 为例,

private void initHandlerMappings(ApplicationContext context) {
		this.handlerMappings = null;
		//首先在applicationContext中获取
		if (this.detectAllHandlerMappings) {
			// Find all HandlerMappings in the ApplicationContext, including ancestor contexts.
			Map<String, HandlerMapping> matchingBeans =
					BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false);
			if (!matchingBeans.isEmpty()) {
				this.handlerMappings = new ArrayList<HandlerMapping>(matchingBeans.values());
				// We keep HandlerMappings in sorted order.
				AnnotationAwareOrderComparator.sort(this.handlerMappings);
			}
		}
		else {
			try {
				HandlerMapping hm = context.getBean(HANDLER_MAPPING_BEAN_NAME, HandlerMapping.class);
				this.handlerMappings = Collections.singletonList(hm);
			}
			catch (NoSuchBeanDefinitionException ex) {
				// Ignore, we'll add a default HandlerMapping later.
			}
		}
		//如果没有自定义handlermapping,则使用默认策略
		if (this.handlerMappings == null) {
			//加载默认策略
			this.handlerMappings = getDefaultStrategies(context, HandlerMapping.class);
			if (logger.isDebugEnabled()) {
				logger.debug("No HandlerMappings found in servlet '" + getServletName() + "': using default");
			}
		}
	}

下面介绍一下getDefaultStrategies 这个方法,贴代码:
从这段代码可以看出:默认策略返回的是个集合,集合如果不为空,则直接返回了集合中的第一个策略配置.

	//strategyInterface 为HandlerMapping.class
	protected <T> List<T> getDefaultStrategies(ApplicationContext context, Class<T> strategyInterface) {
		String key = strategyInterface.getName();
		//从defaultStrategies中获取该策略的值
		String value = defaultStrategies.getProperty(key);
		if (value != null) {
			//多个值之间用逗号分隔
			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) {
						// ... 省略
				}
			}
			return strategies;
		}
		else {
			return new LinkedList<T>();
		}
	}

defaultStrategies ? springmvc都有哪些默认的策略配置?

继续贴代码,springmvc从默认的DispatcherServlet.properties文件中加载默认策略

	//org.springframework.web.servlet.DispatcherServlet
	private static final String DEFAULT_STRATEGIES_PATH = "DispatcherServlet.properties";
	private static final Properties defaultStrategies;
	static {
		try {
			ClassPathResource resource = new ClassPathResource(DEFAULT_STRATEGIES_PATH, DispatcherServlet.class);
			defaultStrategies = PropertiesLoaderUtils.loadProperties(resource);
		}
		catch (IOException ex) {
			throw new IllegalStateException("Could not load '" + DEFAULT_STRATEGIES_PATH + "': " + ex.getMessage());
		}
	}

DispatcherServlet.properties 文件,看看就行了,默认加载第一个配置的

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

springmvc创建完成!

后续更新springmvc怎样处理请求

FrameworkServlet中的模板方法doService在其子类中Dispatchservlet中的具体实现,以及springmvc,通过request获取hangler,根据handler找到对应的handlerAdapt,用handler处理handler,调用processDispatchResult方法处理上面返回的结果(包含找到view并输出渲染给用户),并展示给用户.

概念:

handler:也就是处理器,mvc中的c,可以是类,也可以是方法,所有标注了@RequestMapping注解的方法都可以看成一个handler,只要可以处理请求,那就是一个handler.

handlerMapping:也就是处理器映射器,用来查找handler的,springmvc 会处理很多请求,每个请求都需要一个handler来处理,具体接收到一个请求后需要哪个handler来处理,这就是handlerMapping要做的事情.

handlerAdapt:也就是处理器适配器,springmvc 的handler可以是任意形式,而servlet处理请求的结构却是固定的,如:doService方法,怎么让固定的servlet处理灵活的Handler就是handlerAdapt做的事情.

***不确定有没有后文,所以多加了点常识! ***