SpringMVC源码分析--容器初始化（四）FrameworkServlet

在上一篇博客SpringMVC源码分析--容器初始化（三）HttpServletBean我们介绍了HttpServletBean的init函数，其主要作用是初始化了一下SpringMVC配置文件的地址contextConfigLocation的配置属性，然后其调用的子类FrameworkServlet的initServletBean方法。

其实FrameworkServlet是springMVC初始化IOC容器的核心，通过读取配置的contextConfigLocation配置的springMVC配置文件的地址来读取各种初始化信息和Bean注入信息，来完成springMVC IOC 容器的初始化。接下来我们通过源码一步一步进行分析。

首先我们看initServletBean函数方法，其主要的操作就是this.webApplicationContext = initWebApplicationContext()完成webApplicationContext的初始化，webApplicationContext 即为springMVC的IOC容器，其实现类是XMLWebApplicationContext，

这样我们发现，初始化工作在initWebApplicationContext函数方法中。

//创建springMVC的IOC容器
@Override
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 {
//创建springMVC的IOC容器
this.webApplicationContext = initWebApplicationContext();
//没有任何具体实现
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");
}
}

initWebApplicationContext函数方法是整个springMVC IOC实现的实现过程，函数代码段如下，

WebApplicationContext rootContext =WebApplicationContextUtils.getWebApplicationContext(getServletContext())是从ServletContext中获取IOC容器，因为我们知道spring web在初始化时会将初始化的webApplicationContex保存到ServletContext中，这样我们就可以获取到spring web容器了，并且把它作为父容器。

if (this.webApplicationContext != null) 当容器已经存在时，我们就不需要重新创建，只需要刷新一下，将springMVC配置文件中的属性加载到webApplicationContext中就可以了，当不存在时我们就需要一步一步的创建webApplicationContext了。

wac = findWebApplicationContext()在ServletContext中查找WebApplicationContext，说不定它已经被存放到ServletContext中去了。

如果没有我们就需要创建wac = createWebApplicationContext(rootContext)，这个步骤我们会接下来分析，创建完之后我们调用onRefresh(wac)，这个方法在子类DispatcherServlet中实现，去初始化一些其他操作，现在已经完成了webApplicationContext的初始化工作了接下来就需要把webApplicationContext存放到ServletContext中去了getServletContext().setAttribute(attrName,
wac)，最后调用return wac完成springMVC IOC容器的初始化。

/**
*初始化和发布web应用上下文，封装了建立Spring容器上下文的整个过程
*
*/
protected WebApplicationContext initWebApplicationContext() {
//获取由ContextLoaderListener初始化并注册在ServletContext中的根上下文，一般是Spring的IOC容器记为rootContext
WebApplicationContext rootContext =
WebApplicationContextUtils.getWebApplicationContext(getServletContext());
WebApplicationContext wac = null;
//如果webApplicationContext已经不为空，表示这个Servlet类是通过编程式注册到容器中的(Servlet 3.0 +中的ServletContext.addServlet（）)，
//上下文也由编程式传入。若这个传入的上下文还没有被初始化，将rootContext上下文设置为它的父上下文，然后将其初始化，否则直接使用。
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);
}
}
}
//判断wac是否为空判断是否已经完成上面的上下文的设置
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
//如果为空，说明该Servlet不是由编程式注册到容器中的，在ServletContext中查找上下文，查找得到
//说明上下文已经以别的方式初始化并注册在contextAttribute下，直接使用
wac = findWebApplicationContext();
}
if (wac == null) {
// No context instance is defined for this servlet -> create a local one
//此时还为空，调用以下方法创建一个全新的以rootContext为父上下文的上下文，作为SpringMVC配置元素的上下文
//大多数情况下我们所使用的上下文就是这个新建的上下文
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.
//在DispatcherServlet中复写，会初始化一系列属性
onRefresh(wac);
}

if (this.publishContext) {
// Publish the context as a servlet context attribute.
//将这个上下文发布到ServletContext中，也就是将上下文以一个和Servlet类在web.xml中注册名字有关的值为键
//设置为ServletContext的一个属性
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;
}

上面我们介绍了springMVC IOC容器的初始化操作，但很多具体操作是在其他函数中完成的，接下来我们一一分析，

findWebApplicationContext函数是从ServletContext中查找webApplicationContext，springMVC初始化完成之后我们会看到它会将webApplicationContext保存到ServletContext中，这样我们可以在ServletContext中获取到它。

//从当前容器中查找SpringMVC的IOC容器
protected WebApplicationContext findWebApplicationContext() {
String attrName = getContextAttribute();
if (attrName == null) {
return null;
}
WebApplicationContext wac =
WebApplicationContextUtils.getWebApplicationContext(getServletContext(), attrName);
if (wac == null) {
throw new IllegalStateException("No WebApplicationContext found: initializer not registered?");
}
return wac;
}

在上面介绍中我们并没有真正介绍到webApplicationContext初始化的完整过程，其完整实现是在createWebApplicationContext函数中，其首先会实例化一个IOC容器，这只是一个空容器，并没有相关属性wac =(ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);

接下来的操作就是对wac设置相关属性

wac.setEnvironment(getEnvironment())设置环境

wac.setParent(parent)设置parent,这样就把springMVC和Spring的两个IOC容器连接了在一起

wac.setConfigLocation(getContextConfigLocation())设置web.xml中的springMVC的配置文件，各种bean的注入

configureAndRefreshWebApplicationContext(wac)，这个函数是关键，是解析springMVC配置文件完成初始化的过程。

return wac返回已经初始化的webApplicationContext

//创建springMVC的IOC容器，
protected WebApplicationContext createWebApplicationContext(ApplicationContext parent) {
//获取类XMLWebApplicationContext
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");
}
//实例化一个IOC容器
ConfigurableWebApplicationContext wac =
(ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
//设置IOC容器相关的属性，这样springMVC的IOC容器就创建好了
wac.setEnvironment(getEnvironment());

//设置parent,这样就把springMVC和Spring的两个IOC容器连接了在一起
wac.setParent(parent);
//设置web.xml中的springMVC的配置文件，各种bean的注入
wac.setConfigLocation(getContextConfigLocation());

//初始化springMVC各种的相关配置，各种注入的Controller，配置文件等
configureAndRefreshWebApplicationContext(wac);

return wac;
}

上面我们介绍到configureAndRefreshWebApplicationContext函数是完成springMVC配置文件初始化过程的函数，其实它也是比较简单的，也是设置springMVC IOC容器的相关属性，

最终调用wac.refresh()，通过AbstractApplicationContext来完成对springMVC xml配置文件的解析初始化操作，这边我们就不再深入探究，在spring IOC容器初始化时我们再详细介绍。

/*配置或者刷新应用上下文*/
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());
}
}
//设置springMVC IOC容器的相关属性
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);
//初始化springMVC各种的相关配置，各种注入的Controller，配置文件等
wac.refresh();
}

通过以上函数的操作就完成了springMVC IOC容器的初始化操作，并且把spring web初始化的IOC容器作为父容器，这样springMVC就可以获得父容器中注入的各种Bean，同时初始化的IOC容器webApplicationContext也会被存放到ServletContex中，这样在整个的web容器中都可以得到并使用IOC容器中的各种属性。

FrameworkServlet完整源码解析：

//FrameworkServlet类的设计目的就是用来建立一个和Servlet关联的Spring容器上下文
//并将其注册到ServletContext中，跳脱开SpringMVC体系，我们也能通过继承FrameworkServlet类
//得到与Spring容器整合的好处，FrameworkServlet和HttpServletBean一样，是一个可以独立使用的类

@SuppressWarnings("serial")
public abstract class FrameworkServlet extends HttpServletBean implements ApplicationContextAware {

//servlet命名空间前缀
public static final String DEFAULT_NAMESPACE_SUFFIX = "-servlet";

//FrameworkServlet类的上下文
public static final Class<?> DEFAULT_CONTEXT_CLASS = XmlWebApplicationContext.class;

public static final String SERVLET_CONTEXT_PREFIX = FrameworkServlet.class.getName() + ".CONTEXT.";

private static final String INIT_PARAM_DELIMITERS = ",; \t\n";

private static final boolean responseGetStatusAvailable =
ClassUtils.hasMethod(HttpServletResponse.class, "getStatus");

private String contextAttribute;

private Class<?> contextClass = DEFAULT_CONTEXT_CLASS;

private String contextId;

private String namespace;

// web.xml中配置的contextConfigLocation属性，就是springMVC的配置文件
private String contextConfigLocation;

/** Actual ApplicationContextInitializer instances to apply to the context */
private final List<ApplicationContextInitializer<ConfigurableApplicationContext>> contextInitializers =
new ArrayList<ApplicationContextInitializer<ConfigurableApplicationContext>>();

/** Comma-delimited ApplicationContextInitializer class names set through init param */
private String contextInitializerClasses;

/** Should we publish the context as a ServletContext attribute? */
private boolean publishContext = true;

/** Should we publish a ServletRequestHandledEvent at the end of each request? */
private boolean publishEvents = true;

/** Expose LocaleContext and RequestAttributes as inheritable for child threads? */
private boolean threadContextInheritable = false;

/** Should we dispatch an HTTP OPTIONS request to {@link #doService}? */
private boolean dispatchOptionsRequest = false;

/** Should we dispatch an HTTP TRACE request to {@link #doService}? */
private boolean dispatchTraceRequest = false;

/** WebApplicationContext for this servlet */
private WebApplicationContext webApplicationContext;

/** If the WebApplicationContext was injected via {@link #setApplicationContext} */
private boolean webApplicationContextInjected = false;

/** Flag used to detect whether onRefresh has already been called */
private boolean refreshEventReceived = false;

public FrameworkServlet() {
}

public FrameworkServlet(WebApplicationContext webApplicationContext) {
this.webApplicationContext = webApplicationContext;
}

public void setContextAttribute(String contextAttribute) {
this.contextAttribute = contextAttribute;
}

public String getContextAttribute() {
return this.contextAttribute;
}

public void setContextClass(Class<?> contextClass) {
this.contextClass = contextClass;
}

public Class<?> getContextClass() {
return this.contextClass;
}

public void setContextId(String contextId) {
this.contextId = contextId;
}

public String getContextId() {
return this.contextId;
}

public void setNamespace(String namespace) {
this.namespace = namespace;
}

public String getNamespace() {
return (this.namespace != null ? this.namespace : getServletName() + DEFAULT_NAMESPACE_SUFFIX);
}

//web.xml中配置文件的地址
public void setContextConfigLocation(String contextConfigLocation) {
this.contextConfigLocation = contextConfigLocation;
}

public String getContextConfigLocation() {
return this.contextConfigLocation;
}

@SuppressWarnings("unchecked")
public void setContextInitializers(ApplicationContextInitializer<?>... initializers) {
if (initializers != null) {
for (ApplicationContextInitializer<?> initializer : initializers) {
this.contextInitializers.add((ApplicationContextInitializer<ConfigurableApplicationContext>) initializer);
}
}
}

public void setContextInitializerClasses(String contextInitializerClasses) {
this.contextInitializerClasses = contextInitializerClasses;
}

public void setPublishContext(boolean publishContext) {
this.publishContext = publishContext;
}

public void setPublishEvents(boolean publishEvents) {
this.publishEvents = publishEvents;
}

public void setThreadContextInheritable(boolean threadContextInheritable) {
this.threadContextInheritable = threadContextInheritable;
}

public void setDispatchOptionsRequest(boolean dispatchOptionsRequest) {
this.dispatchOptionsRequest = dispatchOptionsRequest;
}

public void setDispatchTraceRequest(boolean dispatchTraceRequest) {
this.dispatchTraceRequest = dispatchTraceRequest;
}

@Override
public void setApplicationContext(ApplicationContext applicationContext) {
if (this.webApplicationContext == null && applicationContext instanceof WebApplicationContext) {
this.webApplicationContext = (WebApplicationContext) applicationContext;
this.webApplicationContextInjected = true;
}
}

//创建springMVC的IOC容器
@Override
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 {
//创建springMVC的IOC容器
this.webApplicationContext = initWebApplicationContext();
//没有任何具体实现
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");
}
}

/**
*初始化和发布web应用上下文，封装了建立Spring容器上下文的整个过程
*
*/
protected WebApplicationContext initWebApplicationContext() {
//获取由ContextLoaderListener初始化并注册在ServletContext中的根上下文，一般是Spring的IOC容器记为rootContext
WebApplicationContext rootContext =
WebApplicationContextUtils.getWebApplicationContext(getServletContext());
WebApplicationContext wac = null;
//如果webApplicationContext已经不为空，表示这个Servlet类是通过编程式注册到容器中的(Servlet 3.0 +中的ServletContext.addServlet（）)，
//上下文也由编程式传入。若这个传入的上下文还没有被初始化，将rootContext上下文设置为它的父上下文，然后将其初始化，否则直接使用。
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);
}
}
}
//判断wac是否为空判断是否已经完成上面的上下文的设置
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
//如果为空，说明该Servlet不是由编程式注册到容器中的，在ServletContext中查找上下文，查找得到
//说明上下文已经以别的方式初始化并注册在contextAttribute下，直接使用
wac = findWebApplicationContext();
}
if (wac == null) {
// No context instance is defined for this servlet -> create a local one
//此时还为空，调用以下方法创建一个全新的以rootContext为父上下文的上下文，作为SpringMVC配置元素的上下文
//大多数情况下我们所使用的上下文就是这个新建的上下文
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.
//在DispatcherServlet中复写，会初始化一系列属性
onRefresh(wac);
}

if (this.publishContext) {
// Publish the context as a servlet context attribute.
//将这个上下文发布到ServletContext中，也就是将上下文以一个和Servlet类在web.xml中注册名字有关的值为键
//设置为ServletContext的一个属性
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;
}

//从当前容器中查找SpringMVC的IOC容器
protected WebApplicationContext findWebApplicationContext() {
String attrName = getContextAttribute();
if (attrName == null) {
return null;
}
WebApplicationContext wac =
WebApplicationContextUtils.getWebApplicationContext(getServletContext(), attrName);
if (wac == null) {
throw new IllegalStateException("No WebApplicationContext found: initializer not registered?");
}
return wac;
}

//创建springMVC的IOC容器，
protected WebApplicationContext createWebApplicationContext(ApplicationContext parent) {
//获取类XMLWebApplicationContext
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");
}
//实例化一个IOC容器
ConfigurableWebApplicationContext wac =
(ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
//设置IOC容器相关的属性，这样springMVC的IOC容器就创建好了
wac.setEnvironment(getEnvironment());

//设置parent,这样就把springMVC和Spring的两个IOC容器连接了在一起
wac.setParent(parent);
//设置web.xml中的springMVC的配置文件，各种bean的注入
wac.setConfigLocation(getContextConfigLocation());

//初始化springMVC各种的相关配置，各种注入的Controller，配置文件等
configureAndRefreshWebApplicationContext(wac);

return wac;
}
/*配置或者刷新应用上下文*/
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());
}
}
//设置springMVC IOC容器的相关属性
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);
//初始化springMVC各种的相关配置，各种注入的Controller，配置文件等
wac.refresh();
}

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

protected void postProcessWebApplicationContext(ConfigurableWebApplicationContext wac) {
}

protected void applyInitializers(ConfigurableApplicationContext wac) {
String globalClassNames = getServletContext().getInitParameter(ContextLoader.GLOBAL_INITIALIZER_CLASSES_PARAM);
if (globalClassNames != null) {
for (String className : StringUtils.tokenizeToStringArray(globalClassNames, INIT_PARAM_DELIMITERS)) {
this.contextInitializers.add(loadInitializer(className, wac));
}
}

if (this.contextInitializerClasses != null) {
for (String className : StringUtils.tokenizeToStringArray(this.contextInitializerClasses, INIT_PARAM_DELIMITERS)) {
this.contextInitializers.add(loadInitializer(className, wac));
}
}

AnnotationAwareOrderComparator.sort(this.contextInitializers);
for (ApplicationContextInitializer<ConfigurableApplicationContext> initializer : this.contextInitializers) {
initializer.initialize(wac);
}
}

@SuppressWarnings("unchecked")
private ApplicationContextInitializer<ConfigurableApplicationContext> loadInitializer(
String className, ConfigurableApplicationContext wac) {
try {
Class<?> initializerClass = ClassUtils.forName(className, wac.getClassLoader());
Class<?> initializerContextClass =
GenericTypeResolver.resolveTypeArgument(initializerClass, ApplicationContextInitializer.class);
if (initializerContextClass != null) {
Assert.isAssignable(initializerContextClass, wac.getClass(), String.format(
"Could not add context initializer [%s] since its generic parameter [%s] " +
"is not assignable from the type of application context used by this " +
"framework servlet [%s]: ", initializerClass.getName(), initializerContextClass.getName(),
wac.getClass().getName()));
}
return BeanUtils.instantiateClass(initializerClass, ApplicationContextInitializer.class);
}
catch (Exception ex) {
throw new IllegalArgumentException(String.format("Could not instantiate class [%s] specified " +
"via 'contextInitializerClasses' init-param", className), ex);
}
}

public String getServletContextAttributeName() {
return SERVLET_CONTEXT_PREFIX + getServletName();
}

/**
* Return this servlet's WebApplicationContext.
*/
public final WebApplicationContext getWebApplicationContext() {
return this.webApplicationContext;
}

protected void initFrameworkServlet() throws ServletException {
}

public void refresh() {
WebApplicationContext wac = getWebApplicationContext();
if (!(wac instanceof ConfigurableApplicationContext)) {
throw new IllegalStateException("WebApplicationContext does not support refresh: " + wac);
}
((ConfigurableApplicationContext) wac).refresh();
}

//WebApplicationContext刷新通知
public void onApplicationEvent(ContextRefreshedEvent event) {
this.refreshEventReceived = true;
onRefresh(event.getApplicationContext());
}

protected void onRefresh(ApplicationContext context) {
// For subclasses: do nothing by default.
}

/**
* Close the WebApplicationContext of this servlet.
* @see org.springframework.context.ConfigurableApplicationContext#close()
*/
@Override
public void destroy() {
getServletContext().log("Destroying Spring FrameworkServlet '" + getServletName() + "'");
// Only call close() on WebApplicationContext if locally managed...
if (this.webApplicationContext instanceof ConfigurableApplicationContext && !this.webApplicationContextInjected) {
((ConfigurableApplicationContext) this.webApplicationContext).close();
}
}

/**
* Override the parent class implementation in order to intercept PATCH
* requests.
*/
@Override
protected void service(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {

String method = request.getMethod();
if (method.equalsIgnoreCase(RequestMethod.PATCH.name())) {
processRequest(request, response);
}
else {
super.service(request, response);
}
}

//get请求
@Override
protected final void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {

processRequest(request, response);
}

//post请求
@Override
protected final void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {

processRequest(request, response);
}

//put请求
@Override
protected final void doPut(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {

processRequest(request, response);
}

//delete请求
@Override
protected final void doDelete(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {

processRequest(request, response);
}

@Override
protected void doOptions(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {

if (this.dispatchOptionsRequest || CorsUtils.isPreFlightRequest(request)) {
processRequest(request, response);
if (response.containsHeader("Allow")) {
// Proper OPTIONS response coming from a handler - we're done.
return;
}
}

// Use response wrapper for Servlet 2.5 compatibility where
// the getHeader() method does not exist
super.doOptions(request, new HttpServletResponseWrapper(response) {
@Override
public void setHeader(String name, String value) {
if ("Allow".equals(name)) {
value = (StringUtils.hasLength(value) ? value + ", " : "") + RequestMethod.PATCH.name();
}
super.setHeader(name, value);
}
});
}

@Override
protected void doTrace(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {

if (this.dispatchTraceRequest) {
processRequest(request, response);
if ("message/http".equals(response.getContentType())) {
// Proper TRACE response coming from a handler - we're done.
return;
}
}
super.doTrace(request, response);
}

protected final void processRequest(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {

long startTime = System.currentTimeMillis();
Throwable failureCause = null;

LocaleContext previousLocaleContext = LocaleContextHolder.getLocaleContext();
LocaleContext localeContext = buildLocaleContext(request);

RequestAttributes previousAttributes = RequestContextHolder.getRequestAttributes();
ServletRequestAttributes requestAttributes = buildRequestAttributes(request, response, previousAttributes);

WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
asyncManager.registerCallableInterceptor(FrameworkServlet.class.getName(), new RequestBindingInterceptor());

initContextHolders(request, localeContext, requestAttributes);

try {
doService(request, response);
}
catch (ServletException ex) {
failureCause = ex;
throw ex;
}
catch (IOException ex) {
failureCause = ex;
throw ex;
}
catch (Throwable ex) {
failureCause = ex;
throw new NestedServletException("Request processing failed", ex);
}

finally {
resetContextHolders(request, previousLocaleContext, previousAttributes);
if (requestAttributes != null) {
requestAttributes.requestCompleted();
}

if (logger.isDebugEnabled()) {
if (failureCause != null) {
this.logger.debug("Could not complete request", failureCause);
}
else {
if (asyncManager.isConcurrentHandlingStarted()) {
logger.debug("Leaving response open for concurrent processing");
}
else {
this.logger.debug("Successfully completed request");
}
}
}

publishRequestHandledEvent(request, response, startTime, failureCause);
}
}

protected LocaleContext buildLocaleContext(HttpServletRequest request) {
return new SimpleLocaleContext(request.getLocale());
}

protected ServletRequestAttributes buildRequestAttributes(
HttpServletRequest request, HttpServletResponse response, RequestAttributes previousAttributes) {

if (previousAttributes == null || previousAttributes instanceof ServletRequestAttributes) {
return new ServletRequestAttributes(request, response);
}
else {
return null;  // preserve the pre-bound RequestAttributes instance
}
}

private void initContextHolders(
HttpServletRequest request, LocaleContext localeContext, RequestAttributes requestAttributes) {

if (localeContext != null) {
LocaleContextHolder.setLocaleContext(localeContext, this.threadContextInheritable);
}
if (requestAttributes != null) {
RequestContextHolder.setRequestAttributes(requestAttributes, this.threadContextInheritable);
}
if (logger.isTraceEnabled()) {
logger.trace("Bound request context to thread: " + request);
}
}

private void resetContextHolders(HttpServletRequest request,
LocaleContext prevLocaleContext, RequestAttributes previousAttributes) {

LocaleContextHolder.setLocaleContext(prevLocaleContext, this.threadContextInheritable);
RequestContextHolder.setRequestAttributes(previousAttributes, this.threadContextInheritable);
if (logger.isTraceEnabled()) {
logger.trace("Cleared thread-bound request context: " + request);
}
}

private void publishRequestHandledEvent(
HttpServletRequest request, HttpServletResponse response, long startTime, Throwable failureCause) {

if (this.publishEvents) {
// Whether or not we succeeded, publish an event.
long processingTime = System.currentTimeMillis() - startTime;
int statusCode = (responseGetStatusAvailable ? response.getStatus() : -1);
this.webApplicationContext.publishEvent(
new ServletRequestHandledEvent(this,
request.getRequestURI(), request.getRemoteAddr(),
request.getMethod(), getServletConfig().getServletName(),
WebUtils.getSessionId(request), getUsernameForRequest(request),
processingTime, failureCause, statusCode));
}
}

protected String getUsernameForRequest(HttpServletRequest request) {
Principal userPrincipal = request.getUserPrincipal();
return (userPrincipal != null ? userPrincipal.getName() : null);
}

protected abstract void doService(HttpServletRequest request, HttpServletResponse response)
throws Exception;

//监听WebApplicationContext的刷新情况
private class ContextRefreshListener implements ApplicationListener<ContextRefreshedEvent> {

@Override
public void onApplicationEvent(ContextRefreshedEvent event) {
FrameworkServlet.this.onApplicationEvent(event);
}
}

private class RequestBindingInterceptor extends CallableProcessingInterceptorAdapter {

@Override
public <T> void preProcess(NativeWebRequest webRequest, Callable<T> task) {
HttpServletRequest request = webRequest.getNativeRequest(HttpServletRequest.class);
if (request != null) {
HttpServletResponse response = webRequest.getNativeRequest(HttpServletResponse.class);
initContextHolders(request, buildLocaleContext(request), buildRequestAttributes(request, response, null));
}
}
@Override
public <T> void postProcess(NativeWebRequest webRequest, Callable<T> task, Object concurrentResult) {
HttpServletRequest request = webRequest.getNativeRequest(HttpServletRequest.class);
if (request != null) {
resetContextHolders(request, null, null);
}
}
}

}