【源码分析】SpringMVC-DispatchServlet初始化

女爷i 2023-10-11 17:19 70阅读 0赞

*  DispatchServlet继承结构

![在这里插入图片描述][b1bd1ed3a9bb469fb6f76e4f9bb63cd8.png]

*  DispatchServlet的init方法

Tomcat创建Servlet后会执行init方法

发现DispathcheServlet中没有init方法，最终在HttpServletBean中找到了init方法，在init方法中调用了initBeanWrapper，而在该方法中调用了initWebApplicationContext，得到了一个ioc容器，具体研究一下这个方法即可。

protected final void initServletBean() throws ServletException {
        
            this.getServletContext().log("Initializing Spring " + this.getClass().getSimpleName() + " '" + this.getServletName() + "'");
            if (this.logger.isInfoEnabled()) {
        
                this.logger.info("Initializing Servlet '" + this.getServletName() + "'");
            }
    
            long startTime = System.currentTimeMillis();
    
            try {
        
                this.webApplicationContext = this.initWebApplicationContext();
                this.initFrameworkServlet();
            } catch (RuntimeException | ServletException var4) {
        
                this.logger.error("Context initialization failed", var4);
                throw var4;
            }
    
            if (this.logger.isDebugEnabled()) {
        
                String value = this.enableLoggingRequestDetails ? "shown which may lead to unsafe logging of potentially sensitive data" : "masked to prevent unsafe logging of potentially sensitive data";
                this.logger.debug("enableLoggingRequestDetails='" + this.enableLoggingRequestDetails + "': request parameters and headers will be " + value);
            }
    
            if (this.logger.isInfoEnabled()) {
        
                this.logger.info("Completed initialization in " + (System.currentTimeMillis() - startTime) + " ms");
            }
    
        }

initWebApplicationContextrootContext是Spring的容器，Spring的容器一启动就创建好了，并保存在了ServletContext中。

![在这里插入图片描述][watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBARGFuY2VEb25rZXk_size_20_color_FFFFFF_t_70_g_se_x_16]  
紧接着调用了createWebApplicationContext方法，而在这个方法中  
ConfigurableWebApplicationContext wac = (ConfigurableWebApplicationContext)BeanUtils.instantiateClass(contextClass);创建了一个springmvc的ioc容器，紧接着执行了 wac.setParent(parent);将spring的容器设置为父容器，因为controller可能会有属性注入，需要从spring的容器中获取。

protected WebApplicationContext createWebApplicationContext(@Nullable ApplicationContext parent) {
        
            Class<?> contextClass = this.getContextClass();
            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 {
        
                ConfigurableWebApplicationContext wac = (ConfigurableWebApplicationContext)BeanUtils.instantiateClass(contextClass);
                wac.setEnvironment(this.getEnvironment());
                wac.setParent(parent);
                String configLocation = this.getContextConfigLocation();
                if (configLocation != null) {
        
                    wac.setConfigLocation(configLocation);
                }
    
                this.configureAndRefreshWebApplicationContext(wac);
                return wac;
            }
        }

来到了configureAndRefreshWebApplicationContext，在这个方法中，有这么一行代码很关键

wac.addApplicationListener(new SourceFilteringListener(wac, new FrameworkServlet.ContextRefreshListener()));  
给新创建出来的容器添加了一个监听，当springmvc的容器启动完成以后，会进行回调。最后执行了wac.refresh方法进行刷新容器。

protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac) {
        
            if (ObjectUtils.identityToString(wac).equals(wac.getId())) {
        
                if (this.contextId != null) {
        
                    wac.setId(this.contextId);
                } else {
        
                    wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX + ObjectUtils.getDisplayString(this.getServletContext().getContextPath()) + '/' + this.getServletName());
                }
            }
    
            wac.setServletContext(this.getServletContext());
            wac.setServletConfig(this.getServletConfig());
            wac.setNamespace(this.getNamespace());
            wac.addApplicationListener(new SourceFilteringListener(wac, new FrameworkServlet.ContextRefreshListener()));
            ConfigurableEnvironment env = wac.getEnvironment();
            if (env instanceof ConfigurableWebEnvironment) {
        
                ((ConfigurableWebEnvironment)env).initPropertySources(this.getServletContext(), this.getServletConfig());
            }
    
            this.postProcessWebApplicationContext(wac);
            this.applyInitializers(wac);
            wac.refresh();
        }

果然，断点来到了FramewordServlet的回调方法

![在这里插入图片描述][watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBARGFuY2VEb25rZXk_size_20_color_FFFFFF_t_70_g_se_x_16 1]

此时获取到的就是一个完整的IOC容器

![在这里插入图片描述][watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBARGFuY2VEb25rZXk_size_13_color_FFFFFF_t_70_g_se_x_16]  
紧接着调用了本类的onRefresh方法，由于创建的是DispatchServlet，那么来到该类的这个方法，

protected void onRefresh(ApplicationContext context) {
        
            this.initStrategies(context);
        }
    
        protected void initStrategies(ApplicationContext context) {
        
            this.initMultipartResolver(context);
            this.initLocaleResolver(context);
            this.initThemeResolver(context);
            this.initHandlerMappings(context);
            this.initHandlerAdapters(context);
            this.initHandlerExceptionResolvers(context);
            this.initRequestToViewNameTranslator(context);
            this.initViewResolvers(context);
            this.initFlashMapManager(context);
        }

关键的核心就是在这，DispatcherServlet拿到容器以后，从容器中获取了各种组件，并进行了初始化。

以initViewResolvers为例：

private void initViewResolvers(ApplicationContext context) {
        
            this.viewResolvers = null;
            if (this.detectAllViewResolvers) {
        
                Map<String, ViewResolver> matchingBeans = BeanFactoryUtils.beansOfTypeIncludingAncestors(context, ViewResolver.class, true, false);
                if (!matchingBeans.isEmpty()) {
        
                    this.viewResolvers = new ArrayList(matchingBeans.values());
                    AnnotationAwareOrderComparator.sort(this.viewResolvers);
                }
            } else {
        
                try {
        
                    ViewResolver vr = (ViewResolver)context.getBean("viewResolver", ViewResolver.class);
                    this.viewResolvers = Collections.singletonList(vr);
                } catch (NoSuchBeanDefinitionException var3) {
        
                }
            }
    
            if (this.viewResolvers == null) {
        
                this.viewResolvers = this.getDefaultStrategies(context, ViewResolver.class);
                if (this.logger.isTraceEnabled()) {
        
                    this.logger.trace("No ViewResolvers declared for servlet '" + this.getServletName() + "': using default strategies from DispatcherServlet.properties");
                }
            }
    
        }

会先从容器中获取该组件，如果能获取到，则直接赋值，如果不能则使用默认的。  
![在这里插入图片描述][watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBARGFuY2VEb25rZXk_size_20_color_FFFFFF_t_70_g_se_x_16 2]

从容器中获取到该组件后，给this.viewResolvers赋值，并进行了排序，多个视图解析器可进行排序。

springmvcr容器中的HandlerMapping、ViewResolver组件是从哪里来的？  
大家都知道，Spring容器初始化是需要一些BeanDefination的，而这些Bean的定义信息通过debug源码发现是从XmlWebApplicationContext的loadBeanDefinitions方法解析来的。

public class XmlWebApplicationContext extends AbstractRefreshableWebApplicationContext {
        
        public static final String DEFAULT_CONFIG_LOCATION = "/WEB-INF/applicationContext.xml";
        public static final String DEFAULT_CONFIG_LOCATION_PREFIX = "/WEB-INF/";
        public static final String DEFAULT_CONFIG_LOCATION_SUFFIX = ".xml";
    
        public XmlWebApplicationContext() {
        
        }
    
        protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
        
            XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);
            beanDefinitionReader.setEnvironment(this.getEnvironment());
            beanDefinitionReader.setResourceLoader(this);
            beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));
            this.initBeanDefinitionReader(beanDefinitionReader);
            this.loadBeanDefinitions(beanDefinitionReader);
        }
    
        protected void initBeanDefinitionReader(XmlBeanDefinitionReader beanDefinitionReader) {
        
        }
    
        protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws IOException {
        
            String[] configLocations = this.getConfigLocations();
            if (configLocations != null) {
        
                String[] var3 = configLocations;
                int var4 = configLocations.length;
    
                for(int var5 = 0; var5 < var4; ++var5) {
        
                    String configLocation = var3[var5];
                    reader.loadBeanDefinitions(configLocation);
                }
            }
    
        }
    
        protected String[] getDefaultConfigLocations() {
        
            return this.getNamespace() != null ? new String[]{
        "/WEB-INF/" + this.getNamespace() + ".xml"} : new String[]{
        "/WEB-INF/applicationContext.xml"};
        }
    }

![在这里插入图片描述][watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBARGFuY2VEb25rZXk_size_20_color_FFFFFF_t_70_g_se_x_16 3]

在beanDefinitionReader里面有个一registry，而这个对象里面保存了我们要创建哪些bean，除了我们自己定义的一些bean以外，容器自身也提前定义好了一些bean，获取到这些bean的定义信息后，交给IOC容易进行bean的实例化与初始化和属性装配。  
![在这里插入图片描述][watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBARGFuY2VEb25rZXk_size_20_color_FFFFFF_t_70_g_se_x_16 4]

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[watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBARGFuY2VEb25rZXk_size_20_color_FFFFFF_t_70_g_se_x_16]: https://img-blog.csdnimg.cn/2d001b744fb9493ab61c2fba88ea73b4.png?x-oss-process=image/watermark,type_d3F5LXplbmhlaQ,shadow_50,text_Q1NETiBARGFuY2VEb25rZXk=,size_20,color_FFFFFF,t_70,g_se,x_16
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[watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBARGFuY2VEb25rZXk_size_13_color_FFFFFF_t_70_g_se_x_16]: https://img-blog.csdnimg.cn/8ec7f874f7e74c838bc6471e9089a793.png?x-oss-process=image/watermark,type_d3F5LXplbmhlaQ,shadow_50,text_Q1NETiBARGFuY2VEb25rZXk=,size_13,color_FFFFFF,t_70,g_se,x_16
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[watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBARGFuY2VEb25rZXk_size_20_color_FFFFFF_t_70_g_se_x_16 4]: https://img-blog.csdnimg.cn/d25baa3de8fa439ca6dff659dbcfb734.png?x-oss-process=image/watermark,type_d3F5LXplbmhlaQ,shadow_50,text_Q1NETiBARGFuY2VEb25rZXk=,size_20,color_FFFFFF,t_70,g_se,x_16