springmvc源码解析(一),springmvc容器加载的过程

小鱼儿 2022-12-31 01:22 108阅读 0赞

### 文章目录 ###

*   *  了解springmvc
     *  启动流程
     *   *  httpServietBean的init方法
         *  initServletBean方法比较简单:
         *   *  initWebApplicationContext方法是主要初始化子容器,跟dispatcherservlet的方法:
             *   *  createWebApplicationContext就是创建子容器的主要方法:
                 *  onRefresh刷新dispatcherservlet九大组件的主要地方

## 了解springmvc ##

[springmvc官网https://docs.spring.io/spring-framework/docs/current/reference/html/web.html\#mvc-servlet][springmvc_https_docs.spring.io_spring-framework_docs_current_reference_html_web.html_mvc-servlet]

springmvc是基于spring的一个web层框架,同样也是web层框架的有struts,struts2等等,但是struts因为漏洞等问题,被慢慢淘汰了,现在基本都在用springmvc;  
相信以前面试的时候总是背了springmvc的执行流程:  
SpringMVC流程  
1、 用户发送请求至前端控制器DispatcherServlet。

2、 DispatcherServlet收到请求调用HandlerMapping处理器映射器。

3、 处理器映射器找到具体的处理器(可以根据xml配置、注解进行查找)，生成处理器对象及处理器拦截器(如果有则生成)一并返回给DispatcherServlet。

4、 DispatcherServlet调用HandlerAdapter处理器适配器。

5、 HandlerAdapter经过适配调用具体的处理器(Controller,后端控制器)。

6、 Controller执行完成返回ModelAndView。

7、 HandlerAdapter将controller执行结果ModelAndView返回给DispatcherServlet。

8、 DispatcherServlet将ModelAndView传给ViewReslover视图解析器。

9、 ViewReslover解析后返回具体View。

10、DispatcherServlet根据View进行渲染视图（即将模型数据填充至视图中）。

11、 DispatcherServlet响应用户。

虽然背的挺熟,但是没有看过源码,印象总不是很深;因为springmvc基本都有用过,所以有些地方就简述了;  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MzY2MDYz_size_16_color_FFFFFF_t_70]

## 启动流程 ##

首先,我们看一下在web.xml配置的一些东西:

<listener>
    		<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
    	</listener>
    
    	<context-param>
    		<param-name>contextConfigLocation</param-name>
    		<param-value>classpath:/config/beans.xml</param-value>
    	</context-param>
    
    	
    	<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-mvc.xml</param-value>
    		</init-param>
    		<load-on-startup>1</load-on-startup>
    		<async-supported>true</async-supported>
    	</servlet>
    	<servlet-mapping>
    		<servlet-name>SpringMVC</servlet-name>
    		<url-pattern>/</url-pattern>
    	</servlet-mapping>

前面一个是配置spring容器的,后面就是配置springmvc的;DispatcherServlet顾名思义,是一个servlet,先看看DispatcherServlet的类图:  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MzY2MDYz_size_16_color_FFFFFF_t_70 1]

### httpServietBean的init方法 ###

关于servlet就不做过多描述了,servlet入口就是init方法,我们从init方法看,先执行genericServlet的init然后genericServlet又是执行子类httpServietBean的init方法:

@Override
    	public final void init() throws ServletException { 
    		if (logger.isDebugEnabled()) { 
    			logger.debug("Initializing servlet '" + getServletName() + "'");
    		}
    
    		// Set bean properties from init parameters.
    		// 对Servlet初始化参数封装成PropertyValues对象
    		PropertyValues pvs = new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);
    		if (!pvs.isEmpty()) { 
    			try { 
    				//将serlvet封装为BeanWrapper对象
    				BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
    				// 资源加载器
    				ResourceLoader resourceLoader = new ServletContextResourceLoader(getServletContext());
    				// 设置一个属性编辑器
    				bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, getEnvironment()));
    				// 执行init,(留给子类覆盖的,dispatcherServlet都没有覆盖方法,所以是空的)
    				initBeanWrapper(bw);
    				//设置配置
    				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.
    		// 初始化serlvetBean了
    		initServletBean();
    
    		if (logger.isDebugEnabled()) { 
    			logger.debug("Servlet '" + getServletName() + "' configured successfully");
    		}
    	}

### initServletBean方法比较简单: ###

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM4MzY2MDYz_size_16_color_FFFFFF_t_70 2]

#### initWebApplicationContext方法是主要初始化子容器,跟dispatcherservlet的方法: ####

protected WebApplicationContext initWebApplicationContext() { 
    		//获取web.xml配置的spring容器
    		WebApplicationContext rootContext =
    				WebApplicationContextUtils.getWebApplicationContext(getServletContext());
    		WebApplicationContext wac = null;
    
    		// web容器,一般开始为空;springboot项目则不为空;
    		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);
    				}
    			}
    		}
    		// 为空就查找,查找已经绑定的上下文,一般也是空
    		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();
    		}
    		// 根据父容器,创建web容器,就是子容器,这里面子容器进行了刷新
    		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.
    			// 刷新上下文,这里主要加载dispatcherservlet的组件
    			onRefresh(wac);
    		}
    
    		if (this.publishContext) { 
    			// Publish the context as a servlet context attribute.
    			// 将web容器作为servlet上下文属性进行发布
    			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;
    	}

##### createWebApplicationContext就是创建子容器的主要方法: #####

protected WebApplicationContext createWebApplicationContext(WebApplicationContext parent) { 
    		return createWebApplicationContext((ApplicationContext) parent);
    	}
    
    protected WebApplicationContext createWebApplicationContext(ApplicationContext parent) { 
    		// 获取web容器的类型
    		Class<?> contextClass = getContextClass();
    		if (this.logger.isDebugEnabled()) { 
    			this.logger.debug("Servlet with name '" + getServletName() +
    					"' will try to create custom WebApplicationContext context of class '" +
    					contextClass.getName() + "'" + ", using parent context [" + parent + "]");
    		}
    		if (!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)) { 
    			throw new ApplicationContextException(
    					"Fatal initialization error in servlet with name '" + getServletName() +
    					"': custom WebApplicationContext class [" + contextClass.getName() +
    					"] is not of type ConfigurableWebApplicationContext");
    		}
    		// 反射创建web容器
    		ConfigurableWebApplicationContext wac =
    				(ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
    		// 设置环境
    		wac.setEnvironment(getEnvironment());
    		// 设置父容器
    		wac.setParent(parent);
    		//设置配置文件地址
    		wac.setConfigLocation(getContextConfigLocation());
    		// 加载配置,刷新容器
    		configureAndRefreshWebApplicationContext(wac);
    
    		return wac;
    	}

看一下加载配置和刷新容器的地方:

protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac) { 
    		if (ObjectUtils.identityToString(wac).equals(wac.getId())) { 
    			// The application context id is still set to its original default value
    			// -> assign a more useful id based on available information
    			if (this.contextId != null) { 
    				wac.setId(this.contextId);
    			}
    			else { 
    				// Generate default id...
    				wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +
    						ObjectUtils.getDisplayString(getServletContext().getContextPath()) + '/' + getServletName());
    			}
    		}
    		// 设置web容器所属的servletcontext
    		wac.setServletContext(getServletContext());
    		// 设置servletconfig
    		wac.setServletConfig(getServletConfig());
    		// 设置命名空间
    		wac.setNamespace(getNamespace());
    		// 设置监听器
    		wac.addApplicationListener(new SourceFilteringListener(wac, new ContextRefreshListener()));
    
    		// The wac environment's #initPropertySources will be called in any case when the context
    		// is refreshed; do it eagerly here to ensure servlet property sources are in place for
    		// use in any post-processing or initialization that occurs below prior to #refresh
    		ConfigurableEnvironment env = wac.getEnvironment();
    		if (env instanceof ConfigurableWebEnvironment) { 
    			// 刷新之前初始化一些属性资源
    			((ConfigurableWebEnvironment) env).initPropertySources(getServletContext(), getServletConfig());
    		}
    		// web容器的钩子方法,跟spring容器的BeanPostProcess差不多
    		postProcessWebApplicationContext(wac);
    		// 添加一些初始化器,如果没有设置就没有
    		applyInitializers(wac);
    		// 刷新容器就是走的spring容器刷新
    		wac.refresh();
    	}

##### onRefresh刷新dispatcherservlet九大组件的主要地方 #####

onRefresh在frameworkservlet方法里是空的,在dispatcherservlet里重写了onRefresh方法,我们看dispatcherservlet里面的:

@Override
    	protected void onRefresh(ApplicationContext context) { 
    		//初始化九大组件
    		initStrategies(context);
    	}
    
    protected void initStrategies(ApplicationContext context) { 
    		// 初始化文件上传解析器
    		initMultipartResolver(context);
    		// 本地化解析
    		initLocaleResolver(context);
    		// 主题解析器
    		initThemeResolver(context);
    		// 处理器映射器 保存Url映射关系
    		initHandlerMappings(context);
    		// 处理器适配器
    		initHandlerAdapters(context);
    		// 异常解析器
    		initHandlerExceptionResolvers(context);
    		// 视图提取器，从request中获取viemName
    		initRequestToViewNameTranslator(context);
    		// 视图解析器
    		initViewResolvers(context);
    		// 参数解析器
    		initFlashMapManager(context);
    	}

[springmvc_https_docs.spring.io_spring-framework_docs_current_reference_html_web.html_mvc-servlet]: https://docs.spring.io/spring-framework/docs/current/reference/html/web.html#mvc-servlet
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