Spring 启动分析（1）

Spring MVC 启动记录（1）

1、

默认的初始化就是一个DispatchServlet，这个serlet的初始化过程就是整个spring mvc启动的过程。

1-1、默认初始化父类的init方法

GenericServlet的init 

 public void init(ServletConfig config) throws ServletException {
	this.config = config;
	this.init();
 }

 public void init() throws ServletException {

 }

然后调用子类HttpServletBean复写的init方法

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

    // Set bean properties from init parameters.
    try {
        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);
        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();

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

然后调用initServletBean方法，触发子类FrameworkServlet的initServletBean方法调用

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();
			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");
		}
}

其中调用到本地方法initWebApplicationContext方法

protected WebApplicationContext initWebApplicationContext() {
        //获取rootContext
		WebApplicationContext rootContext =
				WebApplicationContextUtils.getWebApplicationContext(getServletContext());
		WebApplicationContext wac = null;

		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);
				}
			}
		}
        //为空则进一步获取
		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();
		}
        //没有则创建
		if (wac == null) {
			// No context instance is defined for this servlet -> create a local one
			wac = createWebApplicationContext(rootContext);
		}
        //创建完刷新
		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;
	}

其中getWebApplicationContext的方法

public static WebApplicationContext getWebApplicationContext(ServletContext sc) {
		return getWebApplicationContext(sc, WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE);
	}

public static WebApplicationContext getWebApplicationContext(ServletContext sc, String attrName) {
		Assert.notNull(sc, "ServletContext must not be null");
		Object attr = sc.getAttribute(attrName);
		if (attr == null) {
			return null;
		}
		if (attr instanceof RuntimeException) {
			throw (RuntimeException) attr;
		}
		if (attr instanceof Error) {
			throw (Error) attr;
		}
		if (attr instanceof Exception) {
			throw new IllegalStateException((Exception) attr);
		}
		if (!(attr instanceof WebApplicationContext)) {
			throw new IllegalStateException("Context attribute is not of type WebApplicationContext: " + attr);
		}
		return (WebApplicationContext) attr;
	}

findWebApplicationContext方法如下：在之前的基础上按照attributeName找不到则全部遍历

public static WebApplicationContext findWebApplicationContext(ServletContext sc) {
		WebApplicationContext wac = getWebApplicationContext(sc);
		if (wac == null) {
			Enumeration<String> attrNames = sc.getAttributeNames();
			while (attrNames.hasMoreElements()) {
				String attrName = attrNames.nextElement();
				Object attrValue = sc.getAttribute(attrName);
				if (attrValue instanceof WebApplicationContext) {
					if (wac != null) {
						throw new IllegalStateException("No unique WebApplicationContext found: more than one " +
								"DispatcherServlet registered with publishContext=true?");
					}
					wac = (WebApplicationContext) attrValue;
				}
			}
		}
		return wac;
	}

没有则进一步创建

FrameworkServlet的方法


protected WebApplicationContext createWebApplicationContext(WebApplicationContext parent) {
		return createWebApplicationContext((ApplicationContext) parent);
}

protected WebApplicationContext createWebApplicationContext(ApplicationContext parent) {
		Class<?> contextClass = getContextClass();
        //默认的context class  XmlWebApplicationContext.class;
		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());

		configureAndRefreshWebApplicationContext(wac);

		return wac;
	}

其中获取contextClass是由FrameworkServlet的本地属性定义

public static final Class<?> DEFAULT_CONTEXT_CLASS = XmlWebApplicationContext.class;

判断完类型后初始化 XmlWebApplicationContext.class这个类

调用BeanUtils的instanceClass方法

BeanUtils
//检查是否为接口或者为空，获取构造器反射类进一步调用
public static <T> T instantiateClass(Class<T> clazz) throws BeanInstantiationException {
		Assert.notNull(clazz, "Class must not be null");
		if (clazz.isInterface()) {
			throw new BeanInstantiationException(clazz, "Specified class is an interface");
		}
		try {
			return instantiateClass(clazz.getDeclaredConstructor());
		}
		catch (NoSuchMethodException ex) {
			throw new BeanInstantiationException(clazz, "No default constructor found", ex);
		}
}
//暴力破解私有构造，调用Constructor实例化一个实例
public static <T> T instantiateClass(Constructor<T> ctor, Object... args) throws BeanInstantiationException {
		Assert.notNull(ctor, "Constructor must not be null");
		try {
			ReflectionUtils.makeAccessible(ctor);
			return ctor.newInstance(args);
		}
		catch (InstantiationException ex) {
			throw new BeanInstantiationException(ctor.getDeclaringClass(),
					"Is it an abstract class?", ex);
		}
		catch (IllegalAccessException ex) {
			throw new BeanInstantiationException(ctor.getDeclaringClass(),
					"Is the constructor accessible?", ex);
		}
		catch (IllegalArgumentException ex) {
			throw new BeanInstantiationException(ctor.getDeclaringClass(),
					"Illegal arguments for constructor", ex);
		}
		catch (InvocationTargetException ex) {
			throw new BeanInstantiationException(ctor.getDeclaringClass(),
					"Constructor threw exception", ex.getTargetException());
		}
	}

直接 获取ServletContext 中的getAttribute调用是否有初始化过的ApplicationContext对象

进而初始化XmlWebApplicationContext类

该类图如下

只有三个默认属性，集成如下，顾初始化所以的父类构造器,继承如下

初始化web xml中的severlet配置到spring的beanwrapper中