文章目录
保持热爱、奔赴山河
14、SpringMVC执行流程
14.1、SpringMVC常用组件
1 DispatcherServlet（前端控制器）
介绍：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
2 HandlerMapping（处理器映射器）
介绍：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
3 Handler（处理器）
介绍：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
4 HandlerAdapter（处理器适配器）
介绍：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
5 ViewResolver（视图解析器）
介绍：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
6 View（视图）
介绍：视图
作用：将模型数据通过页面展示给用户
14.2、DispatcherServlet初始化过程
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。
继承关系
DispatcherServlet
public class DispatcherServlet extends FrameworkServlet {
}
FrameworkServlet
public abstract class FrameworkServlet extends HttpServletBean implements ApplicationContextAware {
}
HttpServletBean
public abstract class HttpServletBean extends HttpServlet implements EnvironmentCapable, EnvironmentAware {
}
HttpServlet
public abstract class HttpServlet extends GenericServlet{
}
GenericServlet
public abstract class GenericServlet implements Servlet, ServletConfig, java.io.Serializable{
}
Servlet
public interface Servlet {
}
1 初始化WebApplicationContext
所在类：org.springframework.web.servlet.FrameworkServlet
@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 {
//初始化 WebApplicationContext
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");
}
}
所在类：org.springframework.web.servlet.FrameworkServlet
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
// 创建WebApplicationContext
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) {
// 刷新WebApplicationContext
onRefresh(wac);
}
}
if (this.publishContext) {
// Publish the context as a servlet context attribute.
// 将IOC容器在应用域共享
String attrName = getServletContextAttributeName();
getServletContext().setAttribute(attrName, wac);
}
return wac;
}
2 创建WebApplicationContext
所在类：org.springframework.web.servlet.FrameworkServlet
protected WebApplicationContext createWebApplicationContext(@Nullable WebApplicationContext parent) {
return createWebApplicationContext((ApplicationContext) parent);
}
所在类：org.springframework.web.servlet.FrameworkServlet
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");
}
// 通过反射创建 IOC 容器对象
ConfigurableWebApplicationContext wac =
(ConfigurableWebApplicationContext) BeanUtils.instantiateClass(contextClass);
wac.setEnvironment(getEnvironment());
// 设置父容器
wac.setParent(parent);
String configLocation = getContextConfigLocation();
if (configLocation != null) {
wac.setConfigLocation(configLocation);
}
configureAndRefreshWebApplicationContext(wac);
return wac;
}
3 DispatcherServlet初始化策略
FrameworkServlet 创建 WebApplicationContext后，刷新容器，调用onRefresh(wac)，此方法在DispatcherServlet中进行了重写，调用了initStrategies(context)方法，初始化策略，即初始化DispatcherServlet的各个组件
所在类：package org.springframework.web.servlet.FrameworkServlet
protected void onRefresh(ApplicationContext context) {
// For subclasses: do nothing by default.
}
所在类：org.springframework.web.servlet.DispatcherServlet
@Override
protected void onRefresh(ApplicationContext context) {
initStrategies(context);
}
所在类：org.springframework.web.servlet.DispatcherServlet
protected void initStrategies(ApplicationContext context) {
initMultipartResolver(context); // 初始化文件上传解析器
initLocaleResolver(context); // 初始化本地解析器
initThemeResolver(context); //
initHandlerMappings(context); // 初始化处理器映射器
initHandlerAdapters(context); // 初始化处理器适配器
initHandlerExceptionResolvers(context); // 初始化异常解析器
initRequestToViewNameTranslator(context); //
initViewResolvers(context); // 初始化视图解析器
initFlashMapManager(context); //
}
14.3、DispatcherServlet调用组件处理请求
1 processRequest()
FrameworkServlet重写HttpServlet中的service()和doXxx()，这些方法中调用了processRequest(request, response)
所在类：org.springframework.web.servlet.FrameworkServlet
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 {
// 执行服务，doService()是一个抽象方法，在DispatcherServlet中进行了重写
doService(request, response);
}
catch (ServletException | 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();
}
logResult(request, response, failureCause, asyncManager);
publishRequestHandledEvent(request, response, startTime, failureCause);
}
}
2 doService()
所在类：org.springframework.web.servlet.DispatcherServlet
@Override
protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
logRequest(request);
// Keep a snapshot of the request attributes in case of an include,
// to be able to restore the original attributes after the include.
Map<String, Object> attributesSnapshot = null;
if (WebUtils.isIncludeRequest(request)) {
attributesSnapshot = new HashMap<>();
Enumeration<?> attrNames = request.getAttributeNames();
while (attrNames.hasMoreElements()) {
String attrName = (String) attrNames.nextElement();
if (this.cleanupAfterInclude || attrName.startsWith(DEFAULT_STRATEGIES_PREFIX)) {
attributesSnapshot.put(attrName, request.getAttribute(attrName));
}
}
}
// Make framework objects available to handlers and view objects.
request.setAttribute(WEB_APPLICATION_CONTEXT_ATTRIBUTE, getWebApplicationContext());
request.setAttribute(LOCALE_RESOLVER_ATTRIBUTE, this.localeResolver);
request.setAttribute(THEME_RESOLVER_ATTRIBUTE, this.themeResolver);
request.setAttribute(THEME_SOURCE_ATTRIBUTE, getThemeSource());
if (this.flashMapManager != null) {
FlashMap inputFlashMap = this.flashMapManager.retrieveAndUpdate(request, response);
if (inputFlashMap != null) {
request.setAttribute(INPUT_FLASH_MAP_ATTRIBUTE, Collections.unmodifiableMap(inputFlashMap));
}
request.setAttribute(OUTPUT_FLASH_MAP_ATTRIBUTE, new FlashMap());
request.setAttribute(FLASH_MAP_MANAGER_ATTRIBUTE, this.flashMapManager);
}
RequestPath previousRequestPath = null;
if (this.parseRequestPath) {
previousRequestPath = (RequestPath) request.getAttribute(ServletRequestPathUtils.PATH_ATTRIBUTE);
ServletRequestPathUtils.parseAndCache(request);
}
try {
// 处理请求和响应
doDispatch(request, response);
}
finally {
if (!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
// Restore the original attribute snapshot, in case of an include.
if (attributesSnapshot != null) {
restoreAttributesAfterInclude(request, attributesSnapshot);
}
}
if (this.parseRequestPath) {
ServletRequestPathUtils.setParsedRequestPath(previousRequestPath, request);
}
}
}
3 doDispatch()
所在类：org.springframework.web.servlet.DispatcherServlet
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
HttpServletRequest processedRequest = request;
HandlerExecutionChain mappedHandler = null;
boolean multipartRequestParsed = false;
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
try {
ModelAndView mv = null;
Exception dispatchException = null;
try {
processedRequest = checkMultipart(request);
multipartRequestParsed = (processedRequest != request);
// Determine handler for the current request.
// Determine handler for the current request.
/*
mappedHandler：调用链
包含handler、interceptorList、interceptorIndex
handler：浏览器发送的请求所匹配的控制器方法
interceptorList：处理控制器方法的所有拦截器集合
interceptorIndex：拦截器索引，控制拦截器afterCompletion()的执行
*/
mappedHandler = getHandler(processedRequest);
if (mappedHandler == null) {
noHandlerFound(processedRequest, response);
return;
}
// Determine handler adapter for the current request.
// 通过控制器方法创建相应的处理器适配器，调用所对应的控制器方法
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
// Process last-modified header, if supported by the handler.
String method = request.getMethod();
boolean isGet = HttpMethod.GET.matches(method);
if (isGet || HttpMethod.HEAD.matches(method)) {
long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
return;
}
}
// 调用拦截器的preHandle()
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
// Actually invoke the handler.
// 由处理器适配器调用具体的控制器方法，最终获得ModelAndView对象
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
applyDefaultViewName(processedRequest, mv);
// 调用拦截器的postHandle()
mappedHandler.applyPostHandle(processedRequest, response, mv);
}
catch (Exception ex) {
dispatchException = ex;
}
catch (Throwable err) {
// As of 4.3, we're processing Errors thrown from handler methods as well,
// making them available for @ExceptionHandler methods and other scenarios.
dispatchException = new NestedServletException("Handler dispatch failed", err);
}
// 后续处理：处理模型数据和渲染视图
processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
}
catch (Exception ex) {
triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
}
catch (Throwable err) {
triggerAfterCompletion(processedRequest, response, mappedHandler,
new NestedServletException("Handler processing failed", err));
}
finally {
if (asyncManager.isConcurrentHandlingStarted()) {
// Instead of postHandle and afterCompletion
if (mappedHandler != null) {
mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
}
}
else {
// Clean up any resources used by a multipart request.
if (multipartRequestParsed) {
cleanupMultipart(processedRequest);
}
}
}
}
4 processDispatchResult()
private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
@Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv,
@Nullable Exception exception) throws Exception {
boolean errorView = false;
if (exception != null) {
if (exception instanceof ModelAndViewDefiningException) {
logger.debug("ModelAndViewDefiningException encountered", exception);
mv = ((ModelAndViewDefiningException) exception).getModelAndView();
}
else {
Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
mv = processHandlerException(request, response, handler, exception);
errorView = (mv != null);
}
}
// Did the handler return a view to render?
if (mv != null && !mv.wasCleared()) {
// 处理模型数据和渲染视图
render(mv, request, response);
if (errorView) {
WebUtils.clearErrorRequestAttributes(request);
}
}
else {
if (logger.isTraceEnabled()) {
logger.trace("No view rendering, null ModelAndView returned.");
}
}
if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
// Concurrent handling started during a forward
return;
}
if (mappedHandler != null) {
// Exception (if any) is already handled..
// 调用拦截器的afterCompletion()
mappedHandler.triggerAfterCompletion(request, response, null);
}
}
14.4、SpringMVC的执行流程
1 DispatcherServlet
用户向服务器发送请求，请求被SpringMVC DispatcherServlet（前端控制器）捕获。
DispatcherServlet（前端控制器）对请求URL进行解析，得到请求资源标识符（URI），判断请求URI对应的映射：
假设请求的url为 : http://localhost:8080/SpringMVC/hello
如上url拆分成三部分：
http://localhost:8080 ------> 服务器域名
SpringMVC ------> 部署在服务器上的web站点
hello ------> 表示控制器方法
通过分析，如上url表示为：请求位于服务器localhost:8080上的SpringMVC站点的hello控制器方法
2 控制器方法不存在
再判断是否配置了
<!--默认servlet处理-->
<mvc:default-servlet-handler></mvc:default-servlet-handler>
<!--开启mvc注解驱动-->
<mvc:annotation-driven/>
如果没配置，则控制台报映射查找不到，客户端展示404错误
如果有配置，则先交给 DispatcherServlet（前端控制器） 处理，处理不了，再交给默认servlet处理，访问目标资源（一般为静态资源，如：JS,CSS,HTML），找不到客户端也会展示404错误
3 控制器方法存在则执行下面的流程
根据该URI，调用HandlerMapping（处理器映射器）获得该Handler（处理器：controller中的方法）配置的所有相关的对象（包括Handler对象以及Handler对象对应的拦截器），最后以HandlerExecutionChain执行链对象的形式返回。
DispatcherServlet 根据获得的 Handler，选择一个合适的HandlerAdapter（处理器适配器），用于执行控制器方法。
如果成功获得HandlerAdapter（处理器适配器），此时将开始执行拦截器的 preHandler(…)方法【正向】
提取Request中的模型数据，填充Handler入参，开始执行Handler（处理器)方法，处理请求。
在填充Handler的入参过程中，根据你的配置，Spring将帮你做一些额外的工作：
4 额外的工作
a HttpMessageConveter（报文信息转换器@RequestBody注解）： 将请求消息（如Json、xml等数据）转换成一个对象，将对象转换为指定的响应信息
b 数据转换：对请求消息进行数据转换。如String转换成Integer、Double等
c 数据格式化：对请求消息进行数据格式化。 如将字符串转换成格式化数字或格式化日期等
d 数据验证： 验证数据的有效性（长度、格式等），验证结果存储到BindingResult或Error中
5 余下步骤
Handler执行完成后，向DispatcherServlet 返回一个ModelAndView对象。
此时将开始执行拦截器的 postHandle(…)方法【逆向】
根据返回的ModelAndView（此时会判断是否存在异常：如果存在异常，则执行HandlerExceptionResolver进行异常处理）选择一个适合的
ViewResolver（视图解析器)进行视图解析，根据Model和View，来渲染视图
渲染视图完毕执行拦截器的afterCompletion(…)方法【逆向】
将渲染结果返回给客户端
14.5、画图
图为SpringMVC的一个较完整的流程图，实线表示SpringMVC框架提供的技术，不需要开发者实现，虚线表示需要开发者实现。