# DispatcherServlet：前端控制器，不需要工程师开发，由框架提供
作用：统一处理请求和响应，整个流程控制的中心，由它调用其它组件处理用户的请求
# HandlerMapping：处理器映射器，不需要工程师开发，由框架提供
作用：根据请求的url、method等信息查找Handler，即控制器方法
# Handler：处理器，需要工程师开发
作用：在DispatcherServlet的控制下Handler对具体的用户请求进行处理
# HandlerAdapter：处理器适配器，不需要工程师开发，由框架提供
作用：通过HandlerAdapter对处理器（控制器方法）进行执行
# ViewResolver：视图解析器，不需要工程师开发，由框架提供
作用：进行视图解析，得到相应的视图，例如：ThymeleafView、InternalResourceView、RedirectView
# View：视图
作用：将模型数据通过页面展示给用户
DispatcherServlet 本质上是一个 Servlet，所以天然的遵循 Servlet 的生命周期。所以宏观上是 Servlet生命周期来进行调度
# 打开DispatcherServlet.java
# DispatcherServlet 继承自FrameworkServlet
public class DispatcherServlet extends FrameworkServlet {
# FrameworkServlet 继承自HttpServletBean
public abstract class FrameworkServlet extends HttpServletBean implements ApplicationContextAware {
# HttpServletBean 继承自HttpServlet
public abstract class HttpServletBean extends HttpServlet implements EnvironmentCapable, EnvironmentAware {
# HttpServlet 继承自GenericServlet
public abstract class HttpServlet extends GenericServlet {
# GenericServlet 实现Servlet接口
public abstract class GenericServlet implements Servlet, ServletConfig, Serializable {
# Servlet 接口
public interface Servlet {
void init(ServletConfig var1) throws ServletException;
ServletConfig getServletConfig();
void service(ServletRequest var1, ServletResponse var2) throws ServletException, IOException;
String getServletInfo();
void destroy();
}
# 查看GenericServlet重写了Servlet 接口中的初始化方法
- 查看左侧重写带上箭头的表示重写了上级接口中的方法
# GenericServlet中初始化方法如下
public void init(ServletConfig config) throws ServletException {
this.config = config;
this.init();
}
# HttpServlet类中没有重写初始化方法
# 查看HttpServletBean类中的初始化方法，调用了initServletBean方法
@Override
public final void init() throws ServletException {
// Set bean properties from init parameters.
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);
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.
initServletBean();
}
# 查看initServletBean方法
protected void initServletBean() throws ServletException {
}
# 查看FrameworkServlet中的initServletBean方法，该类中的initServletBean方法重写的是HttpServletBean中的initServletBean
@Override
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 {
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");
}
}
# 在initServletBean方法中执行如下初始化webApplicationContext
try {
this.webApplicationContext = initWebApplicationContext();
initFrameworkServlet();
}
# 查看initWebApplicationContext方法，通过getWebApplicationContext获取WebApplicationContext ，之后判断是否为空，为空时执行createWebApplicationContext方法
protected WebApplicationContext initWebApplicationContext() {
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);
}
}
}
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();
}
if (wac == null) {
// No context instance is defined for this servlet -> create a local one
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) {
onRefresh(wac);
}
}
if (this.publishContext) {
// Publish the context as a servlet context attribute.
String attrName = getServletContextAttributeName();
getServletContext().setAttribute(attrName, wac);
}
return wac;
}
# 查看createWebApplicationContext方法，调用createWebApplicationContext方法
protected WebApplicationContext createWebApplicationContext(@Nullable WebApplicationContext parent) {
return createWebApplicationContext((ApplicationContext) parent);
}
# 查看createWebApplicationContext方法
protected WebApplicationContext createWebApplicationContext(@Nullable ApplicationContext parent) {
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");
}
// 创建ConfigurableWebApplicationContext 对象
ConfigurableWebApplicationContext wac =
(ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
wac.setEnvironment(getEnvironment());
// spring和springmvc各自有1个容器，这里是将spring的ioc容器设置为springmvc的父容器
wac.setParent(parent);
String configLocation = getContextConfigLocation();
if (configLocation != null) {
wac.setConfigLocation(configLocation);
}
configureAndRefreshWebApplicationContext(wac);
// 最后返回该对象
return wac;
}
# 回到FrameworkServlet类的initWebApplicationContext方法中
if (wac == null) {
// No context instance is defined for this servlet -> create a local one
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) {
// 在上面createWebApplicationContext方法中创建好ConfigurableWebApplicationContext 对象后，刷新
onRefresh(wac);
}
}
if (this.publishContext) {
// Publish the context as a servlet context attribute.
String attrName = getServletContextAttributeName();
// 将创建好的对象添加到共享域中
getServletContext().setAttribute(attrName, wac);
}
# 查看onRefresh方法
protected void onRefresh(ApplicationContext context) {
// For subclasses: do nothing by default.
}
# 查看DispatcherServlet中的onRefresh方法，它重写的是FrameworkServlet类中的onRefresh方法
@Override
protected void onRefresh(ApplicationContext context) {
initStrategies(context);
}
# 查看initStrategies方法
protected void initStrategies(ApplicationContext context) {
// 例如初始化文件上传解析器
initMultipartResolver(context);
initLocaleResolver(context);
initThemeResolver(context);
// 例如初始化处理器映射器
initHandlerMappings(context);
// 例如初始化处理器适配器
initHandlerAdapters(context);
// 例如初始化异常处理器
initHandlerExceptionResolvers(context);
initRequestToViewNameTranslator(context);
// 例如初始化视图解析器
initViewResolvers(context);
initFlashMapManager(context);
}
