概述
Servlet WebApplicationContext容器的初始化基于我们配置的DispatcherServlet，DispatcherServlet是Servlet 的实现，当Servlet进行初始化调用DispatcherServlet的父类HttpServletBean的init方法进行Servlet的初始化。复写Servlet的init方法的关键步骤如下：
- 将web.xml里面的配置进行赋值
- 可以通过4种不同的方式初始化Servlet WebApplicationContext容器，进行配置和刷新
- 初始化HandlerMapping，HandlerAdapter等组件
DispatcherServlet类的UML
我们看关键的几个实现之间的关系和功能
- HttpServletBean : 将ServletConfig里面的配置赋值到Servlet
- FrameworkServlet : 初始化和配置刷新Servlet WebApplicationContext容器
- DispatcherServlet :初始化 Spring MVC的各个组件，以及处理请求
整体流程
- Servlet WebApplicationContext容器的初始化发生在，DispatcherServlet调用HttpServletBean的
init方法，进行Servlet的初始化。主要将ServletConfig里面的配置赋值到Servlet。 - 之后调用FrameworkServlet的
initServletBean方法进行初始化Servlet WebApplicationContext，并配置和刷新上下文 - 最后调用DispatcherServlet的
onRefresh方法，进行组件的初始化
分步解释
调用HttpServletBean的
init方法，将ServletConfig里面的InitParameter赋值到当前Servlet对象中- 将ServletConfig里面的InitParameter配置转为PropertyValues，同时校验必须配置的配置项
- 将PropertyValues里面的配置赋值到Servlet
//org.springframework.web.servlet.HttpServletBean
public final void init() throws ServletException {
// Set bean properties from init parameters.
// 将ServletConfig里面的配置转为PropertyValues，同时校验必须配置的配置项
PropertyValues pvs \= new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);
if (!pvs.isEmpty()) {
try {
BeanWrapper bw \= PropertyAccessorFactory.forBeanPropertyAccess(this);
ResourceLoader resourceLoader \= new ServletContextResourceLoader(getServletContext());
bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, getEnvironment()));
initBeanWrapper(bw);
// 将ServletConfig里面的配置赋值到Servlet
bw.setPropertyValues(pvs, true);
}
catch (BeansException ex) {
if (logger.isErrorEnabled()) {
logger.error("Failed to set bean properties on servlet '" + getServletName() + "'", ex);
}
throw ex;
}
}
// Let subclasses do whatever initialization they like.
//FrameworkServlet进行了重载
initServletBean();
}
将ServletConfig里面的InitParameter配置转为PropertyValues，同时校验必须配置的配置项
- 获取ServletConfig里面的InitParameter转换为PropertyValue
- 将必填的里面的属性去除从InitParameter存在的属性
- 校验是否全部必填的配置是否填
public ServletConfigPropertyValues(ServletConfig config, Set requiredProperties)
throws ServletException {
Set missingProps \= (!CollectionUtils.isEmpty(requiredProperties) ?
new HashSet<>(requiredProperties) : null);
//获取ServletConfig里面的InitParameter转换为PropertyValue
Enumeration paramNames \= config.getInitParameterNames();
while (paramNames.hasMoreElements()) {
String property \= paramNames.nextElement();
Object value \= config.getInitParameter(property);
addPropertyValue(new PropertyValue(property, value));
// 将必填的里面的属性去除从InitParameter存在的属性
if (missingProps != null) {
missingProps.remove(property);
}
}
// Fail if we are still missing properties.
// 校验是否全部必填的配置是否填
if (!CollectionUtils.isEmpty(missingProps)) {
throw new ServletException(
"Initialization from ServletConfig for servlet '" + config.getServletName() +
"' failed; the following required properties were missing: " +
StringUtils.collectionToDelimitedString(missingProps, ", "));
}
}
- //org.springframework.web.servlet.FrameworkServlet
protected final void initServletBean() throws ServletException {
getServletContext().log("Initializing Spring " + getClass().getSimpleName() + " '" + getServletName() + "'");
if (logger.isInfoEnabled()) {
logger.info("Initializing Servlet '" + getServletName() + "'");
}
long startTime \= System.currentTimeMillis();
try {
//初始化上下文
this.webApplicationContext \= initWebApplicationContext();
initFrameworkServlet();
}
catch (ServletException | RuntimeException ex) {
logger.error("Context initialization failed", ex);
throw ex;
}
if (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";
logger.debug("enableLoggingRequestDetails='" + this.enableLoggingRequestDetails +
"': request parameters and headers will be " + value);
}
if (logger.isInfoEnabled()) {
logger.info("Completed initialization in " + (System.currentTimeMillis() - startTime) + " ms");
}
} 调用FrameworkServlet的
initWebApplicationContext进行初始化，方式有四种，先看initWebApplicationContext的方法，然后具体看初始化的方法- 如果已经实例化Servlet WebApplicationContext，那么将父上下文进行赋值，同时配置和刷新Servlet WebApplicationContext上下文
- 如果没有实例化Servlet WebApplicationContext，那么调用findWebApplicationContext方法，从Servlet上下文中通过contextAttribute属性获取
- 如果还是没有实例化Servlet WebApplicationContext，那么调用createWebApplicationContext，通过属性contextClass赋值的常量DEFAULT\_CONTEXT\_CLASS获取类名，然后通过反射进行获取
- 给子类进行一些刷新工作，DispatcherServlet的初始化组件
- 将Servlet WebApplicationContext存储在ServletContext
// org.springframework.web.servlet.FrameworkServlet
protected WebApplicationContext initWebApplicationContext() {
// 从ContextLoaderListener初始化Root WebApplicationContext赋值到ServletContext存储的上下文获取作为父上下文
WebApplicationContext rootContext \=
WebApplicationContextUtils.getWebApplicationContext(getServletContext());
WebApplicationContext wac \= null;
//已经赋值，有两种方式
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
//将RootWebApplicationContext上下文作为父上下文
cwac.setParent(rootContext);
}
//配置并启动上下文
configureAndRefreshWebApplicationContext(cwac);
}
}
}
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
// 从Servlet上下文中通过contextAttribute属性获取
wac \= findWebApplicationContext();
}
if (wac \== null) {
// No context instance is defined for this servlet -> create a local one
//通过属性contextClass赋值的常量DEFAULT\_CONTEXT\_CLASS获取类名，然后通过反射进行获取
wac \= createWebApplicationContext(rootContext);
}
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.
synchronized (this.onRefreshMonitor) {
//给子类进行一些刷新工作，DispatcherServlet的初始化组件
onRefresh(wac);
}
}
//将Servlet WebApplicationContext存储在ServletContext
if (this.publishContext) {
// Publish the context as a servlet context attribute.
String attrName \= getServletContextAttributeName();
getServletContext().setAttribute(attrName, wac);
}
return wac;
}
已经赋值的方式，有两种
通过构造器进行初始化
//org.springframework.web.servlet.FrameworkServlet
public FrameworkServlet(WebApplicationContext webApplicationContext) {
this.webApplicationContext \= webApplicationContext;
}实现ApplicationContextAware接口，调用
setApplicationContext方法进行初始化//org.springframework.web.servlet.FrameworkServlet
public void setApplicationContext(ApplicationContext applicationContext) {
if (this.webApplicationContext \== null && applicationContext instanceof WebApplicationContext) {
//进行初始化
this.webApplicationContext \= (WebApplicationContext) applicationContext;
this.webApplicationContextInjected \= true;
}
}调用FrameworkServlet的
findWebApplicationContext获取上下文- 如果web.xml里面的配置进行了配置，那么会通过HttpServletBean里面将属性contextAttribute赋值，可以获取到attrName
- 从ServletContext上下文中通过属性attrName获取
//org.springframework.web.servlet.FrameworkServlet
protected WebApplicationContext findWebApplicationContext() {
// 如果web.xml里面的配置进行了配置，那么会通过HttpServletBean里面将属性contextAttribute赋值，可以获取到attrName
String attrName \= getContextAttribute();
if (attrName \== null) {
return null;
}
// 从ServletContext上下文中通过属性attrName获取
WebApplicationContext wac \=
WebApplicationContextUtils.getWebApplicationContext(getServletContext(), attrName);
if (wac \== null) {
throw new IllegalStateException("No WebApplicationContext found: initializer not registered?");
}
return wac;
}
* 调用FrameworkServlet的`createWebApplicationContext`进行初始化
* 获取常量DEFAULT\_CONTEXT\_CLASS，也就是XmlWebApplicationContext.class作为上下文的Class类
* 通过反射进行初始化
* 将RootWebApplicationContext作为父容器
* 进行上下文刷新和配置
//org.springframework.web.servlet.FrameworkServlet
protected WebApplicationContext createWebApplicationContext(@Nullable WebApplicationContext parent) {
return createWebApplicationContext((ApplicationContext) parent);
}
//org.springframework.web.servlet.FrameworkServlet
protected WebApplicationContext createWebApplicationContext(@Nullable ApplicationContext parent) {
//获取常量DEFAULT\_CONTEXT\_CLASS，也就是XmlWebApplicationContext.class
Class contextClass \= getContextClass();
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");
}
//通过反射进行初始化
ConfigurableWebApplicationContext wac \=
(ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
wac.setEnvironment(getEnvironment());
//将RootWebApplicationContext作为父容器
wac.setParent(parent);
String configLocation \= getContextConfigLocation();
if (configLocation != null) {
wac.setConfigLocation(configLocation);
}
//进行上下文刷新
configureAndRefreshWebApplicationContext(wac);
return wac;
}
* 调用FrameworkServlet的`configureAndRefreshWebApplicationContext` 进行配置和刷新
* 将ServletContext，ServletConfig，Namespace赋值到上下文
* 添加SourceFilteringListener，用于上下文刷新完毕调用AbstractApplicationContext的`finishRefresh`方法，然后调用AbstractApplicationContext的`publishEvent`发布ContextRefreshListener，监听器监听刷新完毕调用ContextRefreshListener的`onApplicationEvent`方法，然后进行调用`FrameworkServlet.this.onApplicationEvent(event)`用于刷新Spring MVC组件的初始化
* 刷新上下文
protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac) {
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());
}
}
// 将ServletContext，ServletConfig，Namespace赋值到上下文
wac.setServletContext(getServletContext());
wac.setServletConfig(getServletConfig());
wac.setNamespace(getNamespace());
// 添加SourceFilteringListener，用于上下文刷新完毕调用AbstractApplicationContext的finishRefresh方法，然后调用AbstractApplicationContext的publishEvent发布ContextRefreshListener，监听器监听刷新完毕调用ContextRefreshListener的\`onApplicationEvent\`方法，然后进行调用FrameworkServlet.this.onApplicationEvent(event)用于刷新Spring MVC组件的初始化
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);
//刷新上下文
wac.refresh();
}
* 调用DispatcherServlet的`onRefresh`方法进行组件初始化
//org.springframework.web.servlet.DispatcherServlet
@Override
protected void onRefresh(ApplicationContext context) {
initStrategies(context);
}
* 调用DispatcherServlet的`initStrategies`初始化组件
//org.springframework.web.servlet.DispatcherServlet
protected void initStrategies(ApplicationContext context) {
initMultipartResolver(context);
initLocaleResolver(context);
initThemeResolver(context);
initHandlerMappings(context);
initHandlerAdapters(context);
initHandlerExceptionResolvers(context);
initRequestToViewNameTranslator(context);
initViewResolvers(context);
initFlashMapManager(context);
}
- 调用FrameworkServlet的
initServletBean方法进行初始化ServletWebApplicationContext