SpringMVC 执行流程解析
- 1. ContextLoaderListener
- 2. DispatcherServlet 初始化逻辑
- 3. DispatcherServlet 处理流程
- 4. 总结
注:SpringMVC 版本 5.2.15
![](https://img.laitimes.com/img/9ZDMuAjOiMmIsIjOiQnIsICM38FdsYkRGZkRG9lcvx2bjxiNx8VZ6l2cs0TPB50MVR1Tx0EVOBDOsJGcohVYsR2MMBjVtJWd0ckW65UbM5WOHJWa5kHT20ESjBjUIF2X0hXZ0xCMx81dvRWYoNHLrdEZwZ1Rh5WNXp1bwNjW1ZUba9VZwlHdssmch1mclRXY39CXldWYtlWPzNXZj9mcw1ycz9WL49zZuBnL1cjN0AzMxYTMwITNwEjMwIzLc52YucWbp5GZzNmLn9Gbi1yZtl2Lc9CX6MHc0RHaiojIsJye.png)
上面这张图许多人都看过,本文试图从源码的角度带大家分析一下该过程。
1. ContextLoaderListener
首先我们从 ContextLoaderListener 讲起,它继承自 ServletContextListener,用于监听 Web 应用程序的启动与停止。ContextLoaderListener 中的 contextInitialized() 方法用于初始化 Web 应用程序上下文。
ContextLoaderListener # contextInitialized
public class ContextLoaderListener extends ContextLoader implements ServletContextListener {
...
/**
* Initialize the root web application context.
*/
@Override
public void contextInitialized(ServletContextEvent event) {
initWebApplicationContext(event.getServletContext());
}
...
}
其中又调用了 initWebApplicationContext() 方法初始化 Web 应用程序上下文
ContextLoader # initWebApplicationContext
public WebApplicationContext initWebApplicationContext(ServletContext servletContext) {
if (servletContext.getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE) != null) {
throw new IllegalStateException(
"Cannot initialize context because there is already a root application context present - " +
"check whether you have multiple ContextLoader* definitions in your web.xml!");
}
servletContext.log("Initializing Spring root WebApplicationContext");
Log logger = LogFactory.getLog(ContextLoader.class);
if (logger.isInfoEnabled()) {
logger.info("Root WebApplicationContext: initialization started");
}
long startTime = System.currentTimeMillis();
try {
if (this.context == null) {
// 创建并保存应用程序上下文到属性中
this.context = createWebApplicationContext(servletContext);
}
if (this.context instanceof ConfigurableWebApplicationContext) {
ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) this.context;
if (!cwac.isActive()) {
if (cwac.getParent() == null) {
ApplicationContext parent = loadParentContext(servletContext);
cwac.setParent(parent);
}
// 配置并刷新当前 Web 应用程序上下文
configureAndRefreshWebApplicationContext(cwac, servletContext);
}
}
servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.context);
ClassLoader ccl = Thread.currentThread().getContextClassLoader();
if (ccl == ContextLoader.class.getClassLoader()) {
currentContext = this.context;
}
else if (ccl != null) {
currentContextPerThread.put(ccl, this.context);
}
if (logger.isInfoEnabled()) {
long elapsedTime = System.currentTimeMillis() - startTime;
logger.info("Root WebApplicationContext initialized in " + elapsedTime + " ms");
}
return this.context;
}
catch (RuntimeException | Error ex) {
logger.error("Context initialization failed", ex);
servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, ex);
throw ex;
}
}
该方法中调用了 createWebApplicationContext() 方法创建了 Web 应用程序上下文,并调用 configureAndRefreshWebApplicationContext() 方法配置并刷新当前 Web 应用程序上下文。
ContextLoader # configureAndRefreshWebApplicationContext
protected void configureAndRefreshWebApplicationContext(ConfigurableWebApplicationContext wac, ServletContext sc) {
// 为当前 Web 应用程序上下文设置一个 id
if (ObjectUtils.identityToString(wac).equals(wac.getId())) {
String idParam = sc.getInitParameter(CONTEXT_ID_PARAM);
if (idParam != null) {
wac.setId(idParam);
}
else {
wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX +
ObjectUtils.getDisplayString(sc.getContextPath()));
}
}
// 设置 ServletContext
wac.setServletContext(sc);
String configLocationParam = sc.getInitParameter(CONFIG_LOCATION_PARAM);
if (configLocationParam != null) {
wac.setConfigLocation(configLocationParam);
}
ConfigurableEnvironment env = wac.getEnvironment();
if (env instanceof ConfigurableWebEnvironment) {
((ConfigurableWebEnvironment) env).initPropertySources(sc, null);
}
customizeContext(sc, wac);
// 刷新当前应用程序上下文
wac.refresh();
}
该方法的主要作用是刷新当前应用程序上下文,实际上就是调用了 AbstractApplicationContext # refresh 方法,也就是我们常讲的启动 IOC 容器,这个方法里的具体内容这里就不讲了。
总结:
ContextLoaderListener 的作用是准备好 Web 应用程序上下文,启动 IOC 容器。
2. DispatcherServlet 初始化逻辑
先看一张 DispatcherServlet 的继承关系图
其中 HttpServletBean 有一个 init() 方法,该方法是一个初始化方法
HttpServletBean # init
@Override
public final void init() throws ServletException {
// 获取 web.xml 文件中的 <init-param> 中的参数保存到 PropertyValues 中
PropertyValues pvs = new ServletConfigPropertyValues(getServletConfig(), this.requiredProperties);
if (!pvs.isEmpty()) {
try {
// 将 HttpServletBean 对象转换为 BeanWrapper 对象
BeanWrapper bw = PropertyAccessorFactory.forBeanPropertyAccess(this);
// 创建一个 ResourceLoader 对象
ResourceLoader resourceLoader = new ServletContextResourceLoader(getServletContext());
// 注册属性编辑器
bw.registerCustomEditor(Resource.class, new ResourceEditor(resourceLoader, getEnvironment()));
// 初始化 BeanWrapper 对象
initBeanWrapper(bw);
// 将属性值保存到 BeanWrapper 中
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();
}
该方法中首先尝试获取 web.xml 文件中的 init-param 值,如果获取到的话,则将它保存到 BeanWrapper 中。最后调用了 initServletBean() 方法
FrameworkServlet # 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 {
// 初始化 WebApplicationContext
this.webApplicationContext = initWebApplicationContext();
// 空方法,可由子类去具体实现
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");
}
}
该方法中主要调用了 initWebApplicationContext() 去初始化 web 应用程序上下文
FrameworkServlet # initWebApplicationContext
protected WebApplicationContext initWebApplicationContext() {
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) {
cwac.setParent(rootContext);
}
// 配置并刷新 web 应用程序上下文
configureAndRefreshWebApplicationContext(cwac);
}
}
}
if (wac == null) {
// 去获取 web 应用程序上下文
wac = findWebApplicationContext();
}
if (wac == null) {
// 创建 web 应用程序上下文
wac = createWebApplicationContext(rootContext);
}
if (!this.refreshEventReceived) {
synchronized (this.onRefreshMonitor) {
// 刷新 web 应用程序上下文
onRefresh(wac);
}
}
if (this.publishContext) {
String attrName = getServletContextAttributeName();
getServletContext().setAttribute(attrName, wac);
}
return wac;
}
该方法主要是去创建一个新的 web 应用程序上下文,然后调用 onRefresh() 方法
FrameworkServlet # onRefresh
@Override
protected void onRefresh(ApplicationContext context) {
initStrategies(context);
}
DispatcherServlet # initStrategies
protected void initStrategies(ApplicationContext context) {
// 初始化 文件上传解析器
initMultipartResolver(context);
// 初始化 本地化解析器
initLocaleResolver(context);
// 初始化 主题解析器
initThemeResolver(context);
// 初始化 处理器映射器
initHandlerMappings(context);
// 初始化 处理器映射适配器
initHandlerAdapters(context);
// 初始化 异常解析器
initHandlerExceptionResolvers(context);
// 初始化 请求获取视图名转换器
initRequestToViewNameTranslator(context);
// 初始化 视图解析器
initViewResolvers(context);
// 初始化 FlashMap 管理器
initFlashMapManager(context);
}
该方法中初始化了 SpringMVC 的九大组件。我以 initHandlerMappings() 方法为例讲解一下,其他组件的获取方式和它基本相同。
DispatcherServlet # initHandlerMappings
/**
* Initialize the HandlerMappings used by this class.
* <p>If no HandlerMapping beans are defined in the BeanFactory for this namespace,
* we default to BeanNameUrlHandlerMapping.
*/
private void initHandlerMappings(ApplicationContext context) {
this.handlerMappings = null;
// 从 ApplicationContext 中去获取 HandlerMapping
// 获取不到的话去获取对象名为 handlerMapping 的 HandlerMapping 对象
// 再获取不到的话则注册默认的 HandlerMapping
if (this.detectAllHandlerMappings) {
// 从 ApplicationContext 中获取
Map<String, HandlerMapping> matchingBeans =
BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false);
if (!matchingBeans.isEmpty()) {
this.handlerMappings = new ArrayList<>(matchingBeans.values());
AnnotationAwareOrderComparator.sort(this.handlerMappings);
}
}
else {
try {
// 获取名为 handlerMapping 的 HandlerMapping 对象
HandlerMapping hm = context.getBean(HANDLER_MAPPING_BEAN_NAME, HandlerMapping.class);
this.handlerMappings = Collections.singletonList(hm);
}
catch (NoSuchBeanDefinitionException ex) {
}
}
if (this.handlerMappings == null) {
// 注册默认的 HandlerMapping
this.handlerMappings = getDefaultStrategies(context, HandlerMapping.class);
if (logger.isTraceEnabled()) {
logger.trace("No HandlerMappings declared for servlet '" + getServletName() +
"': using default strategies from DispatcherServlet.properties");
}
}
}
该方法首先从 ApplicationContext 中去获取 HandlerMapping,获取不到的话去获取对象名为 handlerMapping 的 HandlerMapping 对象,再获取不到的话则注册默认的 HandlerMapping。我们看一下这个默认的 HandlerMapping 是怎么获取的。
DispatcherServlet # getDefaultStrategies
protected <T> List<T> getDefaultStrategies(ApplicationContext context, Class<T> strategyInterface) {
String key = strategyInterface.getName();
// 获取逻辑在这
String value = defaultStrategies.getProperty(key);
if (value != null) {
// 获取类名
String[] classNames = StringUtils.commaDelimitedListToStringArray(value);
List<T> strategies = new ArrayList<>(classNames.length);
for (String className : classNames) {
try {
// 创建 Class 对象
Class<?> clazz = ClassUtils.forName(className, DispatcherServlet.class.getClassLoader());
Object strategy = createDefaultStrategy(context, clazz);
strategies.add((T) strategy);
}
catch (ClassNotFoundException ex) {
throw new BeanInitializationException(
"Could not find DispatcherServlet's default strategy class [" + className +
"] for interface [" + key + "]", ex);
}
catch (LinkageError err) {
throw new BeanInitializationException(
"Unresolvable class definition for DispatcherServlet's default strategy class [" +
className + "] for interface [" + key + "]", err);
}
}
return strategies;
}
else {
return new LinkedList<>();
}
}
可以看到会尝试从 defaultStrategies 中获取值。然后将获取到的值通过 Class.forName() 方法去创建对象。那么我们看一下这个 defaultStrategies 是什么。
private static final Properties defaultStrategies;
static {
try {
ClassPathResource resource = new ClassPathResource(DEFAULT_STRATEGIES_PATH, DispatcherServlet.class);
defaultStrategies = PropertiesLoaderUtils.loadProperties(resource);
}
catch (IOException ex) {
throw new IllegalStateException("Could not load '" + DEFAULT_STRATEGIES_PATH + "': " + ex.getMessage());
}
}
defaultStrategies 是 DispatcherServlet 中的一个属性,类型为 Properties 。在 DispatcherServlet 的静态代码块中加载了 DispatcherServlet.properties 文件到了 defaultStrategies 中。
DispatcherServlet.properties
org.springframework.web.servlet.LocaleResolver=org.springframework.web.servlet.i18n.AcceptHeaderLocaleResolver
org.springframework.web.servlet.ThemeResolver=org.springframework.web.servlet.theme.FixedThemeResolver
org.springframework.web.servlet.HandlerMapping=org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping,\
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping,\
org.springframework.web.servlet.function.support.RouterFunctionMapping
org.springframework.web.servlet.HandlerAdapter=org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter,\
org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter,\
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter,\
org.springframework.web.servlet.function.support.HandlerFunctionAdapter
org.springframework.web.servlet.HandlerExceptionResolver=org.springframework.web.servlet.mvc.method.annotation.ExceptionHandlerExceptionResolver,\
org.springframework.web.servlet.mvc.annotation.ResponseStatusExceptionResolver,\
org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver
org.springframework.web.servlet.RequestToViewNameTranslator=org.springframework.web.servlet.view.DefaultRequestToViewNameTranslator
org.springframework.web.servlet.ViewResolver=org.springframework.web.servlet.view.InternalResourceViewResolver
org.springframework.web.servlet.FlashMapManager=org.springframework.web.servlet.support.SessionFlashMapManager
在 DispatcherServlet.properties 中定义了 HandlerMapping、HandlerAdapter、ViewResolver 等类。它们的获取逻辑是相似的。通过文件中定义的全限定名,然后调用 Class.forName() 方法去创建对象。
3. DispatcherServlet 处理流程
以 get 请求为例。当发送 get 请求时,由 FrameworkServlet # doGet 方法进行处理。
FrameworkServlet # doGet
@Override
protected final void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
processRequest(request, response);
}
该方法中又调用了 processRequest() 方法
FrameworkServlet # processRequest
protected final void processRequest(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
long startTime = System.currentTimeMillis();
Throwable failureCause = null;
// 获取一个 LocaleContext 对象
LocaleContext previousLocaleContext = LocaleContextHolder.getLocaleContext();
// 构建一个新的 LocaleContext 对象
LocaleContext localeContext = buildLocaleContext(request);
// 获取一个 RequestAttributes 对象
RequestAttributes previousAttributes = RequestContextHolder.getRequestAttributes();
// 构建一个新的 ServletRequestAttributes 对象
ServletRequestAttributes requestAttributes = buildRequestAttributes(request, response, previousAttributes);
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
asyncManager.registerCallableInterceptor(FrameworkServlet.class.getName(), new RequestBindingInterceptor());
// 初始化资源持有者
// 将 localeContext 保存到 LocaleContextHolder 中
// 将 requestAttributes 保存到 RequestContextHolder 中
initContextHolders(request, localeContext, requestAttributes);
try {
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);
}
}
该方法中新建了一个 LocaleContext 对象和一个 ServletRequestAttributes 对象,并保存到了 LocaleContextHolder 与 RequestContextHolder 中。尤其是 RequestContextHolder 对象,我们可以通过它去获取 HttpServletRequest、HttpServletResponse 等对象。最后调用了 doService() 方法。
DispatcherServlet # doService
@Override
protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
logRequest(request);
// 保留 request attributes 的快照
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);
}
try {
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);
}
}
}
}
该方法中又调用了 doDispatch() 方法
DispatcherServlet # doDispatch
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 {
// 检查是否是上传文件的请求
processedRequest = checkMultipart(request);
multipartRequestParsed = (processedRequest != request);
// 获取 HandlerExecutionChain
// 该方法中确定了用哪个处理器处理当前请求
// 并添加了拦截器
mappedHandler = getHandler(processedRequest);
// 没有找到合适的处理器
if (mappedHandler == null) {
noHandlerFound(processedRequest, response);
return;
}
// 获取 HandlerAdapter
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
// 获取请求方法
String method = request.getMethod();
boolean isGet = "GET".equals(method);
if (isGet || "HEAD".equals(method)) {
long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
return;
}
}
// 执行拦截器的前置处理
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
// 处理请求并返回 ModelAndView 对象
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
applyDefaultViewName(processedRequest, mv);
// 执行拦截器的后置处理
mappedHandler.applyPostHandle(processedRequest, response, mv);
}
catch (Exception ex) {
dispatchException = ex;
}
catch (Throwable err) {
dispatchException = new NestedServletException("Handler dispatch failed", err);
}
// 处理最终的结果
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()) {
if (mappedHandler != null) {
mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
}
}
else {
if (multipartRequestParsed) {
cleanupMultipart(processedRequest);
}
}
}
}
接下来我们看一下 getHandler() 方法
DispatcherServlet # getHandler
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
if (this.handlerMappings != null) {
// 遍历所有的 HandlerMapping 去获取 HandlerExecutionChain
for (HandlerMapping mapping : this.handlerMappings) {
HandlerExecutionChain handler = mapping.getHandler(request);
if (handler != null) {
return handler;
}
}
}
return null;
}
该方法中遍历了所有的 HandlerMapping 去获取 Handler
AbstractHandlerMapping # getHandler
public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
// 获取合适的 Handler
Object handler = getHandlerInternal(request);
if (handler == null) {
// 没有找到合适的 Handler,则使用默认的 Handler
handler = getDefaultHandler();
}
if (handler == null) {
return null;
}
// 获取到了该 Handler 的字符串名,则通过字符串名去获取对应的对象
if (handler instanceof String) {
String handlerName = (String) handler;
handler = obtainApplicationContext().getBean(handlerName);
}
// 为当前请求添加拦截器
HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);
if (logger.isTraceEnabled()) {
logger.trace("Mapped to " + handler);
}
else if (logger.isDebugEnabled() && !request.getDispatcherType().equals(DispatcherType.ASYNC)) {
logger.debug("Mapped to " + executionChain.getHandler());
}
if (hasCorsConfigurationSource(handler) || CorsUtils.isPreFlightRequest(request)) {
CorsConfiguration config = (this.corsConfigurationSource != null ? this.corsConfigurationSource.getCorsConfiguration(request) : null);
CorsConfiguration handlerConfig = getCorsConfiguration(handler, request);
config = (config != null ? config.combine(handlerConfig) : handlerConfig);
executionChain = getCorsHandlerExecutionChain(request, executionChain, config);
}
return executionChain;
}
该方法中去获取合适的 Handler,获取失败的话,则会使用默认的 Handler。并为该请求添加拦截器。
RequestMappingInfoHandlerMapping # getHandlerInternal
protected HandlerMethod getHandlerInternal(HttpServletRequest request) throws Exception {
request.removeAttribute(PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE);
try {
return super.getHandlerInternal(request);
}
finally {
ProducesRequestCondition.clearMediaTypesAttribute(request);
}
}
AbstractHandlerMethodMapping # getHandlerInternal
protected HandlerMethod getHandlerInternal(HttpServletRequest request) throws Exception {
// 获取请求路径
String lookupPath = getUrlPathHelper().getLookupPathForRequest(request);
request.setAttribute(LOOKUP_PATH, lookupPath);
// 加读锁
this.mappingRegistry.acquireReadLock();
try {
// 根据请求路径获取对应的 HandlerMethod
HandlerMethod handlerMethod = lookupHandlerMethod(lookupPath, request);
return (handlerMethod != null ? handlerMethod.createWithResolvedBean() : null);
}
finally {
// 释放读锁
this.mappingRegistry.releaseReadLock();
}
}
该方法中根据请求路径去获取对应的 HandlerMethod
AbstractHandlerMethodMapping # lookupHandlerMethod
protected HandlerMethod lookupHandlerMethod(String lookupPath, HttpServletRequest request) throws Exception {
List<Match> matches = new ArrayList<>();
// 根据请求路径获取对应的映射
List<T> directPathMatches = this.mappingRegistry.getMappingsByUrl(lookupPath);
if (directPathMatches != null) {
// 获取匹配的映射
// 这里面会做一系列的比较
// 如:方法名比较、参数比较、请求头比较等
addMatchingMappings(directPathMatches, matches, request);
}
if (matches.isEmpty()) {
// No choice but to go through all mappings...
addMatchingMappings(this.mappingRegistry.getMappings().keySet(), matches, request);
}
// 匹配到合适的方法,则从中找到最匹配的方法
if (!matches.isEmpty()) {
Match bestMatch = matches.get(0);
if (matches.size() > 1) {
Comparator<Match> comparator = new MatchComparator(getMappingComparator(request));
matches.sort(comparator);
bestMatch = matches.get(0);
if (logger.isTraceEnabled()) {
logger.trace(matches.size() + " matching mappings: " + matches);
}
if (CorsUtils.isPreFlightRequest(request)) {
return PREFLIGHT_AMBIGUOUS_MATCH;
}
Match secondBestMatch = matches.get(1);
if (comparator.compare(bestMatch, secondBestMatch) == 0) {
Method m1 = bestMatch.handlerMethod.getMethod();
Method m2 = secondBestMatch.handlerMethod.getMethod();
String uri = request.getRequestURI();
throw new IllegalStateException(
"Ambiguous handler methods mapped for '" + uri + "': {" + m1 + ", " + m2 + "}");
}
}
request.setAttribute(BEST_MATCHING_HANDLER_ATTRIBUTE, bestMatch.handlerMethod);
handleMatch(bestMatch.mapping, lookupPath, request);
return bestMatch.handlerMethod;
}
// 没有找到合适的方法,返回 null
else {
return handleNoMatch(this.mappingRegistry.getMappings().keySet(), lookupPath, request);
}
}
该方法中会去获取与请求最匹配的方法,获取不到则返回 null。
这里就已经获取完 handler 了,也就是一个 HandlerMethod 对象,比如 TestController # test 。我们往下走。
@Controller
public class TestController {
@GetMapping("/test")
public String test() {
return "test";
}
}
DispatcherServlet # getHandlerAdapter
protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {
if (this.handlerAdapters != null) {
for (HandlerAdapter adapter : this.handlerAdapters) {
if (adapter.supports(handler)) {
return adapter;
}
}
}
throw new ServletException("No adapter for handler [" + handler +
"]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler");
}
该方法就是去找一个对应的 HandlerAdapter,一般是 RequestMappingHandlerAdapter。
AbstractHandlerMethodAdapter # handle
public final ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
throws Exception {
return handleInternal(request, response, (HandlerMethod) handler);
}
RequestMappingHandlerAdapter # handleInternal
protected ModelAndView handleInternal(HttpServletRequest request,
HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
ModelAndView mav;
checkRequest(request);
// Execute invokeHandlerMethod in synchronized block if required.
if (this.synchronizeOnSession) {
HttpSession session = request.getSession(false);
if (session != null) {
Object mutex = WebUtils.getSessionMutex(session);
synchronized (mutex) {
mav = invokeHandlerMethod(request, response, handlerMethod);
}
}
else {
// No HttpSession available -> no mutex necessary
mav = invokeHandlerMethod(request, response, handlerMethod);
}
}
else {
// No synchronization on session demanded at all...
mav = invokeHandlerMethod(request, response, handlerMethod);
}
if (!response.containsHeader(HEADER_CACHE_CONTROL)) {
if (getSessionAttributesHandler(handlerMethod).hasSessionAttributes()) {
applyCacheSeconds(response, this.cacheSecondsForSessionAttributeHandlers);
}
else {
prepareResponse(response);
}
}
return mav;
}
该方法中调用了 invokeHandlerMethod() 方法
RequestMappingHandlerAdapter # invokeHandlerMethod
protected ModelAndView invokeHandlerMethod(HttpServletRequest request,
HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
ServletWebRequest webRequest = new ServletWebRequest(request, response);
try {
// 找到 @InitBinder 标注的方法
// @InitBinder 与 WebDatabinder 一起使用,用于注册自定义的属性编辑器
WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);
// 找到 @ModelAttribute 标注的方法
ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);
ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);
// 注册参数解析器
if (this.argumentResolvers != null) {
invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
}
// 注册返回值解析器
if (this.returnValueHandlers != null) {
invocableMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);
}
invocableMethod.setDataBinderFactory(binderFactory);
// 注册参数名发现器
invocableMethod.setParameterNameDiscoverer(this.parameterNameDiscoverer);
ModelAndViewContainer mavContainer = new ModelAndViewContainer();
mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request));
// 调用 @ModelAttribute 标注的方法,保证它在其他方法执行前先被执行
modelFactory.initModel(webRequest, mavContainer, invocableMethod);
mavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect);
AsyncWebRequest asyncWebRequest = WebAsyncUtils.createAsyncWebRequest(request, response);
asyncWebRequest.setTimeout(this.asyncRequestTimeout);
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
asyncManager.setTaskExecutor(this.taskExecutor);
asyncManager.setAsyncWebRequest(asyncWebRequest);
asyncManager.registerCallableInterceptors(this.callableInterceptors);
asyncManager.registerDeferredResultInterceptors(this.deferredResultInterceptors);
if (asyncManager.hasConcurrentResult()) {
Object result = asyncManager.getConcurrentResult();
mavContainer = (ModelAndViewContainer) asyncManager.getConcurrentResultContext()[0];
asyncManager.clearConcurrentResult();
LogFormatUtils.traceDebug(logger, traceOn -> {
String formatted = LogFormatUtils.formatValue(result, !traceOn);
return "Resume with async result [" + formatted + "]";
});
invocableMethod = invocableMethod.wrapConcurrentResult(result);
}
// 调用该方法
invocableMethod.invokeAndHandle(webRequest, mavContainer);
if (asyncManager.isConcurrentHandlingStarted()) {
return null;
}
// 返回 ModelAndView 对象
return getModelAndView(mavContainer, modelFactory, webRequest);
}
finally {
webRequest.requestCompleted();
}
}
该方法中会找到并注册 @InitBinder 标注的方法,找到并调用 @ModelAttribute 标注的的方法。调用 invokeAndHandleI() 方法,最终返回 ModelAndView 对象
ServletInvocableHandlerMethod # invokeAndHandle
public void invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer,
Object... providedArgs) throws Exception {
// 调用方法并获取返回值
Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);
setResponseStatus(webRequest);
if (returnValue == null) {
if (isRequestNotModified(webRequest) || getResponseStatus() != null || mavContainer.isRequestHandled()) {
disableContentCachingIfNecessary(webRequest);
mavContainer.setRequestHandled(true);
return;
}
}
else if (StringUtils.hasText(getResponseStatusReason())) {
mavContainer.setRequestHandled(true);
return;
}
mavContainer.setRequestHandled(false);
Assert.state(this.returnValueHandlers != null, "No return value handlers");
try {
// 使用对应的 HandlerMethodReturnValueHandler 去处理返回值
this.returnValueHandlers.handleReturnValue(
returnValue, getReturnValueType(returnValue), mavContainer, webRequest);
}
catch (Exception ex) {
if (logger.isTraceEnabled()) {
logger.trace(formatErrorForReturnValue(returnValue), ex);
}
throw ex;
}
}
InvocableHandlerMethod # invokeForRequest
public Object invokeForRequest(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,
Object... providedArgs) throws Exception {
// 获取形参值
Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs);
if (logger.isTraceEnabled()) {
logger.trace("Arguments: " + Arrays.toString(args));
}
// 调用方法
return doInvoke(args);
}
InvocableHandlerMethod # getMethodArgumentValues
protected Object[] getMethodArgumentValues(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,
Object... providedArgs) throws Exception {
// 获取 MethodParameter 数组
MethodParameter[] parameters = getMethodParameters();
if (ObjectUtils.isEmpty(parameters)) {
return EMPTY_ARGS;
}
Object[] args = new Object[parameters.length];
for (int i = 0; i < parameters.length; i++) {
MethodParameter parameter = parameters[i];
parameter.initParameterNameDiscovery(this.parameterNameDiscoverer);
args[i] = findProvidedArgument(parameter, providedArgs);
if (args[i] != null) {
continue;
}
if (!this.resolvers.supportsParameter(parameter)) {
throw new IllegalStateException(formatArgumentError(parameter, "No suitable resolver"));
}
try {
// 解析参数
args[i] = this.resolvers.resolveArgument(parameter, mavContainer, request, this.dataBinderFactory);
}
catch (Exception ex) {
// Leave stack trace for later, exception may actually be resolved and handled...
if (logger.isDebugEnabled()) {
String exMsg = ex.getMessage();
if (exMsg != null && !exMsg.contains(parameter.getExecutable().toGenericString())) {
logger.debug(formatArgumentError(parameter, exMsg));
}
}
throw ex;
}
}
return args;
}
该方法中调用了 resolveArgument() 去解析参数
HandlerMethodArgumentResolverComposite # resolveArgument
public Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {
// 获取 HandlerMethodArgumentResolver -> RequestParamMethodArgumentResolver
HandlerMethodArgumentResolver resolver = getArgumentResolver(parameter);
if (resolver == null) {
throw new IllegalArgumentException("Unsupported parameter type [" +
parameter.getParameterType().getName() + "]. supportsParameter should be called first.");
}
// 解析参数
return resolver.resolveArgument(parameter, mavContainer, webRequest, binderFactory);
}
AbstractNamedValueMethodArgumentResolver # resolveArgument
public final Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {
NamedValueInfo namedValueInfo = getNamedValueInfo(parameter);
MethodParameter nestedParameter = parameter.nestedIfOptional();
Object resolvedName = resolveEmbeddedValuesAndExpressions(namedValueInfo.name);
if (resolvedName == null) {
throw new IllegalArgumentException(
"Specified name must not resolve to null: [" + namedValueInfo.name + "]");
}
Object arg = resolveName(resolvedName.toString(), nestedParameter, webRequest);
if (arg == null) {
if (namedValueInfo.defaultValue != null) {
arg = resolveEmbeddedValuesAndExpressions(namedValueInfo.defaultValue);
}
else if (namedValueInfo.required && !nestedParameter.isOptional()) {
handleMissingValue(namedValueInfo.name, nestedParameter, webRequest);
}
arg = handleNullValue(namedValueInfo.name, arg, nestedParameter.getNestedParameterType());
}
else if ("".equals(arg) && namedValueInfo.defaultValue != null) {
arg = resolveEmbeddedValuesAndExpressions(namedValueInfo.defaultValue);
}
if (binderFactory != null) {
WebDataBinder binder = binderFactory.createBinder(webRequest, null, namedValueInfo.name);
try {
arg = binder.convertIfNecessary(arg, parameter.getParameterType(), parameter);
}
catch (ConversionNotSupportedException ex) {
throw new MethodArgumentConversionNotSupportedException(arg, ex.getRequiredType(),
namedValueInfo.name, parameter, ex.getCause());
}
catch (TypeMismatchException ex) {
throw new MethodArgumentTypeMismatchException(arg, ex.getRequiredType(),
namedValueInfo.name, parameter, ex.getCause());
}
}
handleResolvedValue(arg, namedValueInfo.name, parameter, mavContainer, webRequest);
return arg;
}
AbstractNamedValueMethodArgumentResolver # getNamedValueInfo
private NamedValueInfo getNamedValueInfo(MethodParameter parameter) {
// 先从缓存中获取
NamedValueInfo namedValueInfo = this.namedValueInfoCache.get(parameter);
// 缓存中获取不到
if (namedValueInfo == null) {
// 获取 @RequestParam 中的 value 属性值,如果有,则将参数名设置为该值
namedValueInfo = createNamedValueInfo(parameter);
// 如果没有使用 @RequestParam 注解或使用了但没有设置 value 属性
// 则使用 ASM 框架去获取字节码来获取属性名
namedValueInfo = updateNamedValueInfo(parameter, namedValueInfo);
this.namedValueInfoCache.put(parameter, namedValueInfo);
}
return namedValueInfo;
}
RequestParamMethodArgumentResolver # createNamedValueInfo
protected NamedValueInfo createNamedValueInfo(MethodParameter parameter) {
// 根据 @RequestParam 注解去创建 NamedValueInfo
// 如果 @RequestParam 中的 value 属性有值,则设置参数名为该值
RequestParam ann = parameter.getParameterAnnotation(RequestParam.class);
return (ann != null ? new RequestParamNamedValueInfo(ann) : new RequestParamNamedValueInfo());
}
AbstractNamedValueMethodArgumentResolver # updateNamedValueInfo
private NamedValueInfo updateNamedValueInfo(MethodParameter parameter, NamedValueInfo info) {
String name = info.name;
if (info.name.isEmpty()) {
name = parameter.getParameterName();
if (name == null) {
throw new IllegalArgumentException(
"Name for argument of type [" + parameter.getNestedParameterType().getName() +
"] not specified, and parameter name information not found in class file either.");
}
}
String defaultValue = (ValueConstants.DEFAULT_NONE.equals(info.defaultValue) ? null : info.defaultValue);
return new NamedValueInfo(name, info.required, defaultValue);
}
MethodParameter # getParameterName
public String getParameterName() {
if (this.parameterIndex < 0) {
return null;
}
ParameterNameDiscoverer discoverer = this.parameterNameDiscoverer;
if (discoverer != null) {
String[] parameterNames = null;
if (this.executable instanceof Method) {
parameterNames = discoverer.getParameterNames((Method) this.executable);
}
else if (this.executable instanceof Constructor) {
parameterNames = discoverer.getParameterNames((Constructor<?>) this.executable);
}
if (parameterNames != null) {
this.parameterName = parameterNames[this.parameterIndex];
}
this.parameterNameDiscoverer = null;
}
return this.parameterName;
}
LocalVariableTableParameterNameDiscoverer # getParameterNames
public String[] getParameterNames(Method method) {
Method originalMethod = BridgeMethodResolver.findBridgedMethod(method);
return doGetParameterNames(originalMethod);
}
LocalVariableTableParameterNameDiscoverer # doGetParameterNames
private String[] doGetParameterNames(Executable executable) {
Class<?> declaringClass = executable.getDeclaringClass();
Map<Executable, String[]> map = this.parameterNamesCache.computeIfAbsent(declaringClass, this::inspectClass);
return (map != NO_DEBUG_INFO_MAP ? map.get(executable) : null);
}
LocalVariableTableParameterNameDiscoverer # inspectClass
private Map<Executable, String[]> inspectClass(Class<?> clazz) {
// 获取字节码文件
InputStream is = clazz.getResourceAsStream(ClassUtils.getClassFileName(clazz));
if (is == null) {
if (logger.isDebugEnabled()) {
logger.debug("Cannot find '.class' file for class [" + clazz +
"] - unable to determine constructor/method parameter names");
}
return NO_DEBUG_INFO_MAP;
}
try {
ClassReader classReader = new ClassReader(is);
Map<Executable, String[]> map = new ConcurrentHashMap<>(32);
// ASM 框架提升字节码文件
classReader.accept(new ParameterNameDiscoveringVisitor(clazz, map), 0);
return map;
}
catch (IOException ex) {
if (logger.isDebugEnabled()) {
logger.debug("Exception thrown while reading '.class' file for class [" + clazz +
"] - unable to determine constructor/method parameter names", ex);
}
}
catch (IllegalArgumentException ex) {
if (logger.isDebugEnabled()) {
logger.debug("ASM ClassReader failed to parse class file [" + clazz +
"], probably due to a new Java class file version that isn't supported yet " +
"- unable to determine constructor/method parameter names", ex);
}
}
finally {
try {
is.close();
}
catch (IOException ex) {
}
}
return NO_DEBUG_INFO_MAP;
}
走到这一步便是通过 ASM 框架来提升字节码文件获取参数名称了。所以推荐使用 @ReuquestParam 并设置 value 属性值,这样可以直接获取到参数名,避免了 ASM 框架编辑字节码所带来的性能消耗。
DispatcherServlet # 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);
}
}
if (mv != null && !mv.wasCleared()) {
// 渲染 ModelAndView
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..
mappedHandler.triggerAfterCompletion(request, response, null);
}
}
本方法中调用了 render() 方法去渲染视图
DispatcherServlet # render
protected void render(ModelAndView mv, HttpServletRequest request, HttpServletResponse response) throws Exception {
Locale locale =
(this.localeResolver != null ? this.localeResolver.resolveLocale(request) : request.getLocale());
response.setLocale(locale);
View view;
String viewName = mv.getViewName();
if (viewName != null) {
// 根据 viewName 解析出 View
view = resolveViewName(viewName, mv.getModelInternal(), locale, request);
if (view == null) {
throw new ServletException("Could not resolve view with name '" + mv.getViewName() +
"' in servlet with name '" + getServletName() + "'");
}
}
else {
// No need to lookup: the ModelAndView object contains the actual View object.
view = mv.getView();
if (view == null) {
throw new ServletException("ModelAndView [" + mv + "] neither contains a view name nor a " +
"View object in servlet with name '" + getServletName() + "'");
}
}
// Delegate to the View object for rendering.
if (logger.isTraceEnabled()) {
logger.trace("Rendering view [" + view + "] ");
}
try {
if (mv.getStatus() != null) {
response.setStatus(mv.getStatus().value());
}
view.render(mv.getModelInternal(), request, response);
}
catch (Exception ex) {
if (logger.isDebugEnabled()) {
logger.debug("Error rendering view [" + view + "]", ex);
}
throw ex;
}
}
本方法中调用了 resolveViewName() 去获取 View
DispatcherServlet # resolveViewName
protected View resolveViewName(String viewName, @Nullable Map<String, Object> model,
Locale locale, HttpServletRequest request) throws Exception {
if (this.viewResolvers != null) {
for (ViewResolver viewResolver : this.viewResolvers) {
// 使用 ViewResolver 去解析出 View
View view = viewResolver.resolveViewName(viewName, locale);
if (view != null) {
return view;
}
}
}
return null;
}
本方法中找到合适的 ViewResolver 去解析出 View
public View resolveViewName(String viewName, Locale locale) throws Exception {
// 是否启用了缓存功能,默认启用了
if (!isCache()) {
return createView(viewName, locale);
}
else {
// 先尝试从缓存中取 View
Object cacheKey = getCacheKey(viewName, locale);
View view = this.viewAccessCache.get(cacheKey);
if (view == null) {
synchronized (this.viewCreationCache) {
view = this.viewCreationCache.get(cacheKey);
if (view == null) {
// 缓存中没有去到,交给子类去创建 View
view = createView(viewName, locale);
if (view == null && this.cacheUnresolved) {
view = UNRESOLVED_VIEW;
}
if (view != null && this.cacheFilter.filter(view, viewName, locale)) {
this.viewAccessCache.put(cacheKey, view);
this.viewCreationCache.put(cacheKey, view);
}
}
}
}
else {
if (logger.isTraceEnabled()) {
logger.trace(formatKey(cacheKey) + "served from cache");
}
}
return (view != UNRESOLVED_VIEW ? view : null);
}
}
本方法中判断是否开启了视图缓存功能,默认是开启了的。先尝试从缓存中取 View,取不到的话则交给子类去创建 View。
UrlBasedViewResolver # createView
@Override
protected View createView(String viewName, Locale locale) throws Exception {
// 判断该视图解析器是否能处理这个视图
// 如果不能的话,交给其他视图解析器去处理
if (!canHandle(viewName, locale)) {
return null;
}
// 检查前缀是否为 "redirect:"
// 有的话则是请求重定向
if (viewName.startsWith(REDIRECT_URL_PREFIX)) {
// 截取 "redirect:" 后的字符串
String redirectUrl = viewName.substring(REDIRECT_URL_PREFIX.length());
// 创建重定视图
RedirectView view = new RedirectView(redirectUrl,
isRedirectContextRelative(), isRedirectHttp10Compatible());
String[] hosts = getRedirectHosts();
if (hosts != null) {
view.setHosts(hosts);
}
return applyLifecycleMethods(REDIRECT_URL_PREFIX, view);
}
// 检查前缀是否为 "forward:"
// 有的话则是请求转发
if (viewName.startsWith(FORWARD_URL_PREFIX)) {
String forwardUrl = viewName.substring(FORWARD_URL_PREFIX.length());
InternalResourceView view = new InternalResourceView(forwardUrl);
return applyLifecycleMethods(FORWARD_URL_PREFIX, view);
}
// 如果没有加这两个前缀的话,则回调给父类处理
// 其实最终的处理结果是跟请求转发一样的
return super.createView(viewName, locale);
}
该方法中会获取字符串前缀。前缀为 “redirect:” 则是请求重定向,为 “forward:” 则是请求转发。如果没有这两个前缀的话,又回调到父类 AbstractCachingViewResolver # createView 方法中。
AbstractCachingViewResolver # createView
protected View createView(String viewName, Locale locale) throws Exception {
return loadView(viewName, locale);
}
回调到父类 AbstractCachingViewResolver # createView 方法,并调用了 loadView() 方法
InternalResourceViewResolver # buildView
protected AbstractUrlBasedView buildView(String viewName) throws Exception {
// 可以看到,这里创建的 View 类型跟请求转发的相同
InternalResourceView view = (InternalResourceView) super.buildView(viewName);
if (this.alwaysInclude != null) {
view.setAlwaysInclude(this.alwaysInclude);
}
view.setPreventDispatchLoop(true);
return view;
}
本方法中调用了 buildView() 方法创建 View,可以看到,这里创建的 View 类型跟请求转发的相同
UrlBasedViewResolver # buildView
protected AbstractUrlBasedView buildView(String viewName) throws Exception {
Class<?> viewClass = getViewClass();
Assert.state(viewClass != null, "No view class");
AbstractUrlBasedView view = (AbstractUrlBasedView) BeanUtils.instantiateClass(viewClass);
// 拼接上前缀和后缀
// 可以从 web.xml 文件中获取
view.setUrl(getPrefix() + viewName + getSuffix());
view.setAttributesMap(getAttributesMap());
String contentType = getContentType();
if (contentType != null) {
view.setContentType(contentType);
}
String requestContextAttribute = getRequestContextAttribute();
if (requestContextAttribute != null) {
view.setRequestContextAttribute(requestContextAttribute);
}
Boolean exposePathVariables = getExposePathVariables();
if (exposePathVariables != null) {
view.setExposePathVariables(exposePathVariables);
}
Boolean exposeContextBeansAsAttributes = getExposeContextBeansAsAttributes();
if (exposeContextBeansAsAttributes != null) {
view.setExposeContextBeansAsAttributes(exposeContextBeansAsAttributes);
}
String[] exposedContextBeanNames = getExposedContextBeanNames();
if (exposedContextBeanNames != null) {
view.setExposedContextBeanNames(exposedContextBeanNames);
}
return view;
}
本方法中将 viewName 拼接了前缀和后缀,获取到的便是最终的完整路径。这里并将 View 获取成功了。
AbstractView # render
public void render(@Nullable Map<String, ?> model, HttpServletRequest request,
HttpServletResponse response) throws Exception {
if (logger.isDebugEnabled()) {
logger.debug("View " + formatViewName() +
", model " + (model != null ? model : Collections.emptyMap()) +
(this.staticAttributes.isEmpty() ? "" : ", static attributes " + this.staticAttributes));
}
// 创建并合并属性到 Map 中
// 如:保存到 ModelAndView 或 Model 中的属性
Map<String, Object> mergedModel = createMergedOutputModel(model, request, response);
// 准备好 HttpServletResponse 对象
prepareResponse(request, response);
// 解析出视图
renderMergedOutputModel(mergedModel, getRequestToExpose(request), response);
}
该方法中主要是将我们自己保存到 ModelAndView 或 Model 中的属性转换为 Map 对象。最后调用 renderMergedOutputModel() 方法。
InternalResourceView # renderMergedOutputModel
protected void renderMergedOutputModel(
Map<String, Object> model, HttpServletRequest request, HttpServletResponse response) throws Exception {
// 将属性保存到 request 域中
exposeModelAsRequestAttributes(model, request);
// Expose helpers as request attributes, if any.
exposeHelpers(request);
// 确定请求的 url
String dispatcherPath = prepareForRendering(request, response);
// 获取一个请求转发器
RequestDispatcher rd = getRequestDispatcher(request, dispatcherPath);
if (rd == null) {
throw new ServletException("Could not get RequestDispatcher for [" + getUrl() +
"]: Check that the corresponding file exists within your web application archive!");
}
// 是一个 include 请求,jsp 中经常用到,实现 jsp 页面的复用
if (useInclude(request, response)) {
response.setContentType(getContentType());
if (logger.isDebugEnabled()) {
logger.debug("Including [" + getUrl() + "]");
}
rd.include(request, response);
}
else {
if (logger.isDebugEnabled()) {
logger.debug("Forwarding to [" + getUrl() + "]");
}
// 请求转发
rd.forward(request, response);
}
}
4. 总结
SpringMVC 处理请求的大致流程就是这样了。内容有点多,建议最好还是自己 debug 走一遍代码,梳理出整个脉络才好。