spring学习-DispatcherServlet的初始化

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我是靠谱客的博主洁净小鸭子，最近开发中收集的这篇文章主要介绍spring学习-DispatcherServlet的初始化，觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

1.servlet容器（如：tomcat）载入web.xml，读取context-param以及listener的配置，初始化ServletContext作为所有servlet的父上下文环境。
2.spring为我们提供的IOC容器，需要我们指定容器的配置文件，然后由该监听器初始化并创建该容器。要求你指定配置文件的地址及文件名称，一定要使用：contextConfigLocation作为参数名称
3.IOC容器会去初始化webApplicationContext加载配置在contextConfigLocation参数下的配置文件，将其中的参数初始化为对象加入到webApplicationContext中作为之后所有的Servlet的父上下文环境
这里写图片描述
4.初始化DispatcherServlet。
4.1调用Servlet中的init（ServletConfig Config）方法

public void init(ServletConfig config) throws ServletException;

4.2这个方法在GenericServlet中实现

public void init(ServletConfig config) throws ServletException {
    this.config = config;//加载当前servlet的配置
    this.init();//这个方法在GenericServlet中是空实现留给子类初始化
    }

4.3HttpServletBean

public final void init() throws ServletException {
        if (logger.isDebugEnabled()) {
            logger.debug("Initializing servlet '" + getServletName() + "'");
        }

        // Set bean properties from init parameters.
        try {
            //这里的代码就是将Servlet包装成一个bean然后初始化它的参数
            PropertyValues pvs = new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);
            BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
            ResourceLoader resourceLoader = new ServletContextResourceLoader(getServletContext());
            bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, getEnvironment()));
            initBeanWrapper(bw);//这个是留给子类实现初始化的，但是DispatcherServlet没有用这个方法，所以上面的代码基本无关
            bw.setPropertyValues(pvs, true);
        }
        catch (BeansException ex) {
            logger.error("Failed to set bean properties on servlet '" + getServletName() + "'", ex);
            throw ex;
        }

        // Let subclasses do whatever initialization they like.
        initServletBean();//这个方法是DispatcherServlet用来初始化的方法

        if (logger.isDebugEnabled()) {
            logger.debug("Servlet '" + getServletName() + "' configured successfully");
        }
    }

4.4FrameworkServlet

protected final void initServletBean() throws ServletException {
        getServletContext().log("Initializing Spring FrameworkServlet '" + getServletName() + "'");
        if (this.logger.isInfoEnabled()) {
            this.logger.info("FrameworkServlet '" + getServletName() + "': initialization started");
        }
        long startTime = System.currentTimeMillis();

        try {
            this.webApplicationContext = initWebApplicationContext();//DispatcherServlet通过这个方法进行初始化
            initFrameworkServlet();
        }
        catch (ServletException ex) {
            this.logger.error("Context initialization failed", ex);
            throw ex;
        }
        catch (RuntimeException ex) {
            this.logger.error("Context initialization failed", ex);
            throw ex;
        }

        if (this.logger.isInfoEnabled()) {
            long elapsedTime = System.currentTimeMillis() - startTime;
            this.logger.info("FrameworkServlet '" + getServletName() + "': initialization completed in " +
                    elapsedTime + " ms");
        }
    }

4.5

protected WebApplicationContext initWebApplicationContext() {
  //这个方法是得到双亲上下文,但是当DispatcherServlet初始时得到的是null
        WebApplicationContext rootContext =
                WebApplicationContextUtils.getWebApplicationContext(getServletContext());
        WebApplicationContext wac = null;

        //如果得到双亲上下文就进行初始化
        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);
                }
            }
        }

        //下面就是查找当前servlet的webApplicationContext存不存在，不存在就创建一个
        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();
        }
        if (wac == null) {
            // No context instance is defined for this servlet -> create a local one
            wac = createWebApplicationContext(rootContext);//下一步就进入到了该方法中
        }

        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.
            onRefresh(wac);
        }

        if (this.publishContext) {
            // Publish the context as a servlet context attribute.
            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;
    }

4.6

protected WebApplicationContext createWebApplicationContext(ApplicationContext parent) {
        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");
        }
        ConfigurableWebApplicationContext wac =
                (ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);

        wac.setEnvironment(getEnvironment());
        wac.setParent(parent);
        wac.setConfigLocation(getContextConfigLocation());
        //以上就是创建webApplicationContext

        configureAndRefreshWebApplicationContext(wac);

        return wac;
    }

4.7

protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac) {
        //该方法进行了上下文容器初始化
        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());
            }
        }

        wac.setServletContext(getServletContext());
        wac.setServletConfig(getServletConfig());
        wac.setNamespace(getNamespace());
        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) {
            ((ConfigurableWebEnvironment) env).initPropertySources(getServletContext(), getServletConfig());
        }

        postProcessWebApplicationContext(wac);
        applyInitializers(wac);
        wac.refresh();
    }

5通过以上几步即可创建一个完整的IOC容器，而完成容器创建之后，DispatcherServlet还做了一件事：初始化Servelt控制器必备对象，这个是在initWebApplicationContext()方法中通过调用onRefresh(wac)方法实现的。

DispatcherServlet

/**
     * This implementation calls {@link #initStrategies}.
     */
    @Override
    protected void onRefresh(ApplicationContext context) {
        initStrategies(context);
    }

    /**
     * Initialize the strategy objects that this servlet uses.
     * <p>May be overridden in subclasses in order to initialize further strategy objects.
     */
    protected void initStrategies(ApplicationContext context) {
        initMultipartResolver(context);
        initLocaleResolver(context);
        initThemeResolver(context);
        initHandlerMappings(context);
        initHandlerAdapters(context);
        initHandlerExceptionResolvers(context);
        initRequestToViewNameTranslator(context);
        initViewResolvers(context);
        initFlashMapManager(context);
    }

加载各类工具。

以上就是我现在的理解，还很粗浅，等我理解深刻一点了再来细化。