SpringMVC源码解析七(初始化过程解析)
在SpringMVC中处理请求的核心类是DispatcherServlet; SpringMVC在DispatcherServlet类的doDispatch()中维护着请求处理流程的主要逻辑
DispatcherServlet的继承关系图:
SpringMVC初始化的触发点:
SpringMVC的初始化是从HttpServletBean#init()开始的;Tomcat在启动时最终会调用GenericServlet#init(javax.servlet.ServletConfig), 在该方法中又调用了GenericServlet#init()方法; 由于HttpServletBean继承了GenericServlet并重写了init()方法, 所以此时调用的是HttpServletBean#init(), 从这里便开始了SpringMVC的初始化历程
GenericServlet#init(javax.servlet.ServletConfig)方法实现:
@Override
public void init(ServletConfig config) throws ServletException {
this.config = config;
this.init();
}GenericServlet#init()方法实现(实际上执行的是HttpServletBean#init()方法):
public void init() throws ServletException {
// NOOP by default
}HttpServletBean#init()方法实现:
@Override
public final void init() throws ServletException {
if (logger.isDebugEnabled()) {
logger.debug("Initializing servlet '" + getServletName() + "'");
}
//PropertyValues: 获取Web.xml里面的servlet的init-param（web.xml）
PropertyValues pvs = new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);
if (!pvs.isEmpty()) {
try {
//BeanWrapper: 封装了bean的行为，提供了设置和获取属性值，它有对应的BeanWrapperImpl
BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
//ResourceLoader: 可以根据一个资源地址加载文件资源。classpath:这种方式指定SpringMVC框架bean配置文件的来源
ResourceLoader resourceLoader = new ServletContextResourceLoader(getServletContext());
bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, getEnvironment()));
initBeanWrapper(bw);
bw.setPropertyValues(pvs, true);
}
catch (BeansException ex) {
if (logger.isErrorEnabled()) {
logger.error("Failed to set bean properties on servlet '" + getServletName() + "'", ex);
}
throw ex;
}
}
/**
* 由子类实现, 进行子类的初始化
* {@link FrameworkServlet#initServletBean()}
*/
initServletBean();
if (logger.isDebugEnabled()) {
logger.debug("Servlet '" + getServletName() + "' configured successfully");
}
}Tomcat部分讲解:
Tomcat在启动后会逐步加载各个组件, 最终会加载到Wrapper容器, 因此会调用StandardWrapper#load()方法; 在此之前的启动逻辑感兴趣的可以看这篇博客:Tomcat源码解析五(容器的启动过程解析)
StandardWrapper#load()方法实现:
@Override
public synchronized void load() throws ServletException {
/**
* 加载Servlet
*/
instance = loadServlet();
if (!instanceInitialized) {
initServlet(instance);
}
if (isJspServlet) {
StringBuilder oname = new StringBuilder(getDomain());
oname.append(":type=JspMonitor");
oname.append(getWebModuleKeyProperties());
oname.append(",name=");
oname.append(getName());
oname.append(getJ2EEKeyProperties());
try {
jspMonitorON = new ObjectName(oname.toString());
Registry.getRegistry(null, null).registerComponent(instance, jspMonitorON, null);
} catch (Exception ex) {
log.warn("Error registering JSP monitoring with jmx " + instance);
}
}
}StandardWrapper#loadServlet()方法实现:
public synchronized Servlet loadServlet() throws ServletException {
// 如果我们已经有实例或实例池，则无需执行任何操作
if (!singleThreadModel && (instance != null))
return instance;
PrintStream out = System.out;
if (swallowOutput) {
SystemLogHandler.startCapture();
}
Servlet servlet;
try {
long t1=System.currentTimeMillis();
// Complain if no servlet class has been specified
if (servletClass == null) {
unavailable(null);
throw new ServletException
(sm.getString("standardWrapper.notClass", getName()));
}
InstanceManager instanceManager = ((StandardContext)getParent()).getInstanceManager();
try {
/**
* 实例化Servlet
*/
servlet = (Servlet) instanceManager.newInstance(servletClass);
} catch (ClassCastException e) {
. . . . . .
}
if (multipartConfigElement == null) {
MultipartConfig annotation =
servlet.getClass().getAnnotation(MultipartConfig.class);
if (annotation != null) {
multipartConfigElement =
new MultipartConfigElement(annotation);
}
}
if (servlet instanceof ContainerServlet) {
((ContainerServlet) servlet).setWrapper(this);
}
classLoadTime=(int) (System.currentTimeMillis() -t1);
if (servlet instanceof SingleThreadModel) {
if (instancePool == null) {
instancePool = new Stack<>();
}
singleThreadModel = true;
}
/**
* 初始化Servlet
*/
initServlet(servlet);
fireContainerEvent("load", this);
loadTime=System.currentTimeMillis() -t1;
} finally {
. . . . . .
}
return servlet;
}分析:
- 通过反射实例化Servlet (Servlet ==> DispatcherServlet)
- 初始化Servlet
(1) Tomcat是如何获取到SpringMVC的核心类DispatcherServlet然后进行初始化的呢?
在web.xml中有这样的一个配置:
spring-mvc
org.springframework.web.servlet.DispatcherServlet
1
spring-mvc
/
Tomcat中在Context容器启动时会发送消息通知各个观察者, 其中有一个观察者就是WebConfig, WebConfig在监听到消息之后,开始解析web.xml, 并对其中配置的Servlet逐个进行实例化, 其中就包括我们配置的DispatcherServlet路径信息; 所以Tomcat就可以通过反射去实例化该类;
解析web.xml配置信息以及实例化DispatcherServlet可以看org.apache.catalina.startup.ContextConfig#webConfig() == > org.apache.catalina.startup.ContextConfig#configureContext(WebXml webxml) 相关逻辑
调用链如下:
org.apache.catalina.core.StandardWrapper#setServletClass(String servletClass)方法是将DispatcherServlet类信息维护到StandardWrapper实例中(每一个StandardWrapper对应一个Servlet)
(2) 初始化Servlet
StandardWrapper#initServlet(Servlet servlet)方法实现: (Servlet => DispatcherServlet)
private synchronized void initServlet(Servlet servlet) throws ServletException {
if (instanceInitialized && !singleThreadModel) return;
// 调用此Servlet的初始化方法
try {
if( Globals.IS_SECURITY_ENABLED) {
boolean success = false;
try {
Object[] args = new Object[] { facade };
/**
* 通过反射执行该Servlet的init()方法
*/
SecurityUtil.doAsPrivilege("init", servlet, classType, args);
success = true;
} finally {
if (!success) {
// destroy() will not be called, thus clear the reference now
SecurityUtil.remove(servlet);
}
}
} else {
servlet.init(facade);
}
instanceInitialized = true;
} catch (UnavailableException f) {
. . . . . .
}
}
GenericServlet#init(javax.servlet.ServletConfig)方法实现:
@Override
public void init(ServletConfig config) throws ServletException {
this.config = config;
this.init();
}HttpServletBean#init()方法实现:
@Override
public final void init() throws ServletException {
if (logger.isDebugEnabled()) {
logger.debug("Initializing servlet '" + getServletName() + "'");
}
//PropertyValues: 获取Web.xml里面的servlet的init-param（web.xml）
PropertyValues pvs = new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);
if (!pvs.isEmpty()) {
try {
//BeanWrapper: 封装了bean的行为，提供了设置和获取属性值，它有对应的BeanWrapperImpl
BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
//ResourceLoader: 可以根据一个资源地址加载文件资源。classpath:这种方式指定SpringMVC框架bean配置文件的来源
ResourceLoader resourceLoader = new ServletContextResourceLoader(getServletContext());
bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, getEnvironment()));
initBeanWrapper(bw);
bw.setPropertyValues(pvs, true);
}
catch (BeansException ex) {
if (logger.isErrorEnabled()) {
logger.error("Failed to set bean properties on servlet '" + getServletName() + "'", ex);
}
throw ex;
}
}
/**
* 由子类实现, 进行子类的初始化
* {@link FrameworkServlet#initServletBean()}
*/
initServletBean();
if (logger.isDebugEnabled()) {
logger.debug("Servlet '" + getServletName() + "' configured successfully");
}
}调用链如下:
FrameworkServlet#initServletBean()方法实现: (注意: FrameworkServlet是HttpServletBean的子类)
@Override
protected final void initServletBean() throws ServletException {
getServletContext().log("Initializing Spring FrameworkServlet '" + getServletName() + "'");
if (logger.isInfoEnabled()) {
logger.info("FrameworkServlet '" + getServletName() + "': initialization started");
}
long startTime = System.currentTimeMillis();
try {
/**
* 初始化应用上下文
*/
this.webApplicationContext = initWebApplicationContext();
//初始化FrameworkServlet
initFrameworkServlet();
}
catch (ServletException | RuntimeException ex) {
logger.error("Context initialization failed", ex);
throw ex;
}
if (logger.isInfoEnabled()) {
long elapsedTime = System.currentTimeMillis() - startTime;
logger.info("FrameworkServlet '" + getServletName() + "': initialization completed in " +
elapsedTime + " ms");
}
}分析:
- 初始化应用上下文
- 初始化FrameworkServlet(为空方法)
FrameworkServlet#initWebApplicationContext()方法实现:
protected WebApplicationContext initWebApplicationContext() {
//获取根节点上下文,通过ContextLoaderListener加载,服务器启动便加载
WebApplicationContext rootContext =
WebApplicationContextUtils.getWebApplicationContext(getServletContext());
WebApplicationContext wac = null;
if (this.webApplicationContext != null) {
wac = this.webApplicationContext;
if (wac instanceof ConfigurableWebApplicationContext) {
ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) wac;
if (!cwac.isActive()) {
if (cwac.getParent() == null) {
//设置根节点上下文为父上下文
cwac.setParent(rootContext);
}
//设置id等等
configureAndRefreshWebApplicationContext(cwac);
}
}
}
if (wac == null) {
/**
* 查找servletContext中已有的WebApplicationContext作为上下文
*/
wac = findWebApplicationContext();
}
if (wac == null) {
/**
* 尝试获取本地已有上下文失败, 创建一个本地上下文
*/
wac = createWebApplicationContext(rootContext);
}
if (!this.refreshEventReceived) {
synchronized (this.onRefreshMonitor) {
onRefresh(wac);
}
}
if (this.publishContext) {
// 将DispatcherServlet的上下文放入servlet上下文中
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;
}分析:
- 尝试从ServletContext中获取已有的WebApplicationContext作为上下文
- 尝试获取本地已有上下文失败, 创建一个本地上下文
FrameworkServlet#createWebApplicationContext(org.springframework.context.ApplicationContext)方法实现:
protected WebApplicationContext createWebApplicationContext(@Nullable ApplicationContext parent) {
Class contextClass = getContextClass();
. . .
//通过反射创建mvc容器
ConfigurableWebApplicationContext wac =
(ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
//设置环境
wac.setEnvironment(getEnvironment());
//设置根上下文为父上下文
wac.setParent(parent);
//设置springmvc.xml的路径
String configLocation = getContextConfigLocation();
if (configLocation != null) {
wac.setConfigLocation(configLocation);
}
/**
* 初始化springmvc容器
*/
configureAndRefreshWebApplicationContext(wac);
return wac;
}分析: 利用反射创建一个WebApplicationContext实例, 并进行相关配置设置, 最后调用初始化方法, 开始SpringMVC容器的初始化
FrameworkServlet#configureAndRefreshWebApplicationContext()方法实现:
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(getServletContext().getContextPath()) + '/' + getServletName());
}
}
wac.setServletContext(getServletContext());
wac.setServletConfig(getServletConfig());
wac.setNamespace(getNamespace());
/**
* 向容器中添加监听器, 监听容器初始化结束事件(事件对象:ContextRefreshListener) <=== 重点
* ContextRefreshListener为FrameworkServlet的内部类
*/
wac.addApplicationListener(new SourceFilteringListener(wac, new ContextRefreshListener()));
ConfigurableEnvironment env = wac.getEnvironment();
if (env instanceof ConfigurableWebEnvironment) {
((ConfigurableWebEnvironment) env).initPropertySources(getServletContext(), getServletConfig());
}
postProcessWebApplicationContext(wac);
applyInitializers(wac);
/**
* 调用Spring中的refresh()方法, 刷新应用环境
* {@link AbstractApplicationContext#refresh()}
*/
wac.refresh();
}分析:
- 注册监听器, 用于监听Spring中IOC容器初始化结束事件, 监听到事件后, 从容器中获取相关组件Bean, 注册到SpringMVC上下文中
- 对ConfigurableWebApplicationContext进行相关配置, 然后调用AbstractApplicationContext#refresh()开始SpringMVC相关配置文件的解析(注:WebApplicationContext与AbstractApplicationContext都继承于ApplicationContext); Spring在refresh()方法执行结束, 也就是容器加载完成, 发送结束事件, 由SimpleApplicationEventMulticaster激活监听器SourceFilteringListener的相关方法, 最终会触发DispatcherServlet的initStrategies(ApplicationContext context)方法, 开始各个组件的注册
_1. FrameworkServlet的内部监听器类ContextRefreshListener实现:
private class ContextRefreshListener implements ApplicationListener {
@Override
public void onApplicationEvent(ContextRefreshedEvent event) {
FrameworkServlet.this.onApplicationEvent(event);
}
} 分析: 当监听者获取到事件后调用FrameworkServlet#onApplicationEvent方法进行处理;
_2.AbstractApplicationContext#finishRefresh实现(refresh()方法实现已省略, 需要看该方法内相关逻辑的可以看Spring源码解析专栏):
protected void finishRefresh() {
//清除上下文级别的资源缓存（例如来自扫描的ASM元数据）
clearResourceCaches();
//为此上下文初始化生命周期处理器
initLifecycleProcessor();
//首先将刷新传播到生命周期处理器
getLifecycleProcessor().onRefresh();
/**
* 发布结束事件(事件对象:ContextRefreshedEvent)
*/
publishEvent(new ContextRefreshedEvent(this));
// Participate in LiveBeansView MBean, if active.
LiveBeansView.registerApplicationContext(this);
}AbstractApplicationContext#publishEvent(org.springframework.context.ApplicationEvent)
==> AbstractApplicationContext#publishEvent(java.lang.Object, org.springframework.core.ResolvableType)
==> SimpleApplicationEventMulticaster#multicastEvent
==> SimpleApplicationEventMulticaster#invokeListener
==> SimpleApplicationEventMulticaster#doInvokeListener
==> SourceFilteringListener#onApplicationEvent
==> SourceFilteringListener#onApplicationEventInternal实现:
protected void onApplicationEventInternal(ApplicationEvent event) {
if (this.delegate == null) {
throw new IllegalStateException(
"Must specify a delegate object or override the onApplicationEventInternal method");
}
/**
* 通过监听适配器调用对应监听器的onApplicationEvent()方法
*/
this.delegate.onApplicationEvent(event);
}GenericApplicationListenerAdapter#onApplicationEvent实现:
@Override
public void onApplicationEvent(ApplicationEvent event) {
/**
* GenericApplicationListenerAdapter适配器中维护着真正的监听器
*/
this.delegate.onApplicationEvent(event);
}FrameworkServlet#onApplicationEvent实现:
public void onApplicationEvent(ContextRefreshedEvent event) {
this.refreshEventReceived = true;
synchronized (this.onRefreshMonitor) {
onRefresh(event.getApplicationContext());
}
}DispatcherServlet#onRefresh实现:
@Override
protected void onRefresh(ApplicationContext context) {
initStrategies(context);
}DispatcherServlet#initStrategies实现:
protected void initStrategies(ApplicationContext context) {
initMultipartResolver(context);
initLocaleResolver(context);
initThemeResolver(context);
initHandlerMappings(context);
initHandlerAdapters(context);
initHandlerExceptionResolvers(context);
initRequestToViewNameTranslator(context);
initViewResolvers(context);
initFlashMapManager(context);
}分析: 在这个方法中完成了SpringMVC各个组件的注册, 注意参数是应用上下文ApplicationContext, SpringMVC便可以通过ApplicationContext从容器中获取到自己的组件对象, 然后进行注册; 关于各个组件的初始化就比较简单了, 这里不再进行解析;
调用链如下:
问题: 为什么要这么做呢?
答: 因为IOC, Spring的控制反转, SpringMVC将对象初始化相关操作交由Spring容器去管理, 等容器初始化完成后, 直接从容器中获取需要的组件对象, 再注册到SpringMVC的中容器中即可
SpringMVC宏观启动过程如下:
Tomcat ==> SpringMVC ==> Spring ==> SpringMVC
流程图(Tomcat启动流程+SpringMVC启动流程):
至此, SpringMVC初始化过程解析完成;
相关文章:
SpringMVC源码解析一(在Spring源码项目中搭建SpringMVC源码模块)
SpringMVC源码解析二(请求过程解析)
SpringMVC源码解析三(处理映射器HandlerMapping的解析)
SpringMVC源码解析四(处理适配器HandlerAdapter的解析)
SpringMVC源码解析五(HandlerMethod执行过程解析)
SpringMVC源码解析六(ModelAndView解析)
SpringMVC源码解析七(初始化过程解析)