SpringMVC源码情操陶冶-DispatcherServlet父类简析

2022-11-15 10:18:35

阅读源码有助于陶冶情操，本文对springmvc作个简单的向导

springmvc-web.xml配置

<servlet>

        <servlet-name>dispatch</servlet-name>

        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>

        <!--springmvc配置文件加载路径-->

        <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>dispatch</servlet-name>

        <url-pattern>/</url-pattern>

    </servlet-mapping>

DispatcherServlet类结构

查看源码可以得知类结构如下

DispatcherServlet extends FrameworkServlet

FrameworkServlet extends HttpServletBean implements ApplicationContextAware

HttpServletBean extends HttpServlet implements EnvironmentCapable, EnvironmentAware

本文将对Dispatcher的父类作下向导，方便读者以及博主自我查阅

HttpServletBean-web服务抽象类

具体的介绍可以详看官方注释，这里我们只关注它的init方法，代码如下

//开始初始化springmvc servlet，并实例化相应的PropertyValues供子类调用

public final void init() throws ServletException {

		if (logger.isDebugEnabled()) {

			logger.debug("Initializing servlet '" + getServletName() + "'");

		}

		// Set bean properties from init parameters.

		try {

		//此处便是读取<servlet>节点中的<init-param>参数保存至MutablePropertyValues#propertyValueList集合中

			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()));

			//默认为空

			initBeanWrapper(bw);

			//将bean与属性关联

			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.供子类复写

		initServletBean();

		if (logger.isDebugEnabled()) {

			logger.debug("Servlet '" + getServletName() + "' configured successfully");

		}

	}

小结：

从以上代码可见只是简单的获取servlet中的<init-param>参数并绑定到BeanWrapper对象中，并通过initServletBean()方法供子类完善其余的功能。

FrameworkServlet-结合spring的web抽象类

官方简单的解释为：Spring的web基本servlet框架，通过基于javaBean解决方式来集合Spring的application context上下文。

ApplicationContextAware接口

该接口的使用主要是为当前类可以拥有spring application context上下文类，可方便的获取bean对象，内部只有一个接口方法setApplicationContext(ApplicationContext app)，在FrameworkServlet中的实现

public void setApplicationContext(ApplicationContext applicationContext) {

		//由spring调用并进行相应的applicationContext的注入

		if (this.webApplicationContext == null && applicationContext instanceof WebApplicationContext) {

			this.webApplicationContext = (WebApplicationContext) applicationContext;

			this.webApplicationContextInjected = true;

		}

	}

doService()-抽象接口

主要是供子类去实现处理servlet的请求
复写initServletBean()方法，完善功能

@Override

protected final void initServletBean() throws ServletException {

		//打印我们熟悉的日志

		getServletContext().log("Initializing Spring FrameworkServlet '" + getServletName() + "'");

		if (this.logger.isInfoEnabled()) {

			this.logger.info("FrameworkServlet '" + getServletName() + "': initialization started");

		}

		//对该方法的初始化时间作下统计

		long startTime = System.currentTimeMillis();

		try {

			//此处的初始化操作类似于ContextLoader#initWebApplicationContext

			this.webApplicationContext = initWebApplicationContext();

			//供子类调用去初始化另外的功能

			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");

		}

	}

承接initServletBean()方法的initWebApplicationContext()，代码如下

protected WebApplicationContext initWebApplicationContext() {

		//一般来说,spring初始化时间比springmvc要早，所以rootContext一般都存在

		WebApplicationContext rootContext =				WebApplicationContextUtils.getWebApplicationContext(getServletContext());

		WebApplicationContext wac = null;

		//先检查spring是否已经注入了webApplicationContext，其中的刷新操作类似于`ContextLoader#initWebApplicationContext`，初次调用此处为空

		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()) {

					if (cwac.getParent() == null) {

						//springmvc的父类为spring上下文

						cwac.setParent(rootContext);

					}

					//此处方法不同于`ContextLoader`的相同方法

					configureAndRefreshWebApplicationContext(cwac);

				}

			}

		}

		//再而尝试从ServletContext的`contextAttribute`对应的值去获取

		if (wac == null) {

			wac = findWebApplicationContext();

		}

		//不然则创建新的webApplicationContext

		if (wac == null) {

			wac = createWebApplicationContext(rootContext);

		}

		//springmvc的第一次刷新

		if (!this.refreshEventReceived) {

			//调用子类的onRefresh(wac)方法初始化springmvc

			onRefresh(wac);

		}

		//保存至servletContext属性中

		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;

	}

FrameworkServlet#createWebApplicationContext()-springmvc创建上下文对象

protected WebApplicationContext createWebApplicationContext(ApplicationContext parent) {

		//默认为XmlWebApplicationContext.class也可指定contextClass属性在web.xml

		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);

		//设置springmvc的配置文件即 contextConfigLocation属性

		wac.setConfigLocation(getContextConfigLocation());

		//此处与ContextLoader#configureAndRefreshWebApplicationContext()类似

		configureAndRefreshWebApplicationContext(wac);

		return wac;

	}

承接createWebApplicationContext方法的FrameworkServlet#configureAndRefreshWebApplicationContext()-springmvc的刷新处理，不同于spring

protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac) {

		//设置id属性

		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(getServletContext().getContextPath()) + "/" + getServletName());

			}

		}

		wac.setServletContext(getServletContext());

		wac.setServletConfig(getServletConfig());

		//默认的namespace为getServletName()+"-servlet"

		wac.setNamespace(getNamespace());

		wac.addApplicationListener(new SourceFilteringListener(wac, new ContextRefreshListener()));

		ConfigurableEnvironment env = wac.getEnvironment();

		if (env instanceof ConfigurableWebEnvironment) {

			((ConfigurableWebEnvironment) env).initPropertySources(getServletContext(), getServletConfig());

		}

		//空方法

		postProcessWebApplicationContext(wac);

		//读取web.xml中的`context-param`节点中的globalInitializerClasses、contextInitializerClasses并初始化

		applyInitializers(wac);

		//刷新，此处可见Spring源码情操陶冶-AbstractApplicationContext博文

		wac.refresh();

	}

小结：

FrameworkServlet实例化springmvc上下文环境，与spring初始化上下文环境类似

onRefresh()方法开放出来供子类DispatherServlet调用完善springmvc的相关初始化操作

读取init-param为contextConfigLocation属性的值用于加载springmvc的配置文件，其中的bean文件的读取操作可参照Spring源码情操陶冶-AbstractApplicationContext博文

springmvc的namespace为getServletName()+'-servlet'，比如dispatcher-servlet，用于未指定contextConfigLocation属性的话，便会去加载\WEB-INF\${namespace}.xml，比如\WEB-INF\dispatcher-servlet.xml，而对于spring，默认加载的为\WEB-INF\applicationContext.xml

applicationContext.xml和dispatcher-servlet配置文件的加载，既支持classpath方式的加载，也支持WEB-INF方式的加载。后者是通过ServletContextResourceLoader加载的，实质是通过ServletContext.getRealPath()方法加载web环境下的web-inf的资源，其中参数必须以"/"为开头

下节预告

SpringMVC源码情操陶冶-DispatcherServlet类简析

码农公寓

springmvc-web.xml配置

DispatcherServlet类结构

HttpServletBean-web服务抽象类

FrameworkServlet-结合spring的web抽象类

下节预告

相关文章