本篇将会以Servlet为切入点，通过源码来看web容器中的Controller是如何注册到HandlerMApping中。请求来了之后，web容器是如何根据请求路径找到对应的Controller方法并执行的。
先讲下本文的大概思路和流程图：
5. controller发现和使用流程图
正文开始
Servlet接口的源码
public interface Servlet {
//初始化
public void init(ServletConfig config) throws ServletException;
//响应请求
public void service(ServletRequest req, ServletResponse res)
throws ServletException, IOException;
//获取servlet信息
public String getServletInfo();
//服务停止时回调
public void destroy();
}
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springboot内置了tomcat容器，而tomcat容器是遵循了servlet规范的。servlet规范中定义了初始化、响应、获取配置信息和销毁时回调钩子。从servlet的规范中可以看出，tomcat启动时会调用servlet的init方法，处理请求时会调用service方法，容器销毁时会调用destroy方法。servlet中最核心的实现就是我们所熟知的DispatchServlet，看下DispatchServlet的继承体系
从DispatchServlet的继承体系中，看下Servlet的初始化做了什么。
HttpServletBean中的init方法源码
@Override
public final void init() throws ServletException {
// 设置servlet的属性
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;
}
}
// 具体的初始化方法交给子类实现
initServletBean();
}
//空实现，具体的由子类实现
protected void initServletBean() throws ServletException {
}
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从HttpServletBean中的init方法可以看到，这里核心的就是设置了Servlet的一些 bean properties，继续到子类 FrameworkServlet中看initServletBean方法
@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 {
//这里初始化了web的上下文，这里会初始化Servlet的九大策略
this.webApplicationContext = initWebApplicationContext();
//这个方法也是空实现
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");
}
}
//初始化上下文
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);
}
configureAndRefreshWebApplicationContext(cwac);
}
}
}
if (wac == null) {
wac = findWebApplicationContext();
}
if (wac == null) {
wac = createWebApplicationContext(rootContext);
}
if (!this.refreshEventReceived) {
synchronized (this.onRefreshMonitor) {
//springboot只会进入这个方法，这个方法是空实现，具体实现在子类DispatchServlet
onRefresh(wac);
}
}
if (this.publishContext) {
String attrName = getServletContextAttributeName();
getServletContext().setAttribute(attrName, wac);
}
return wac;
}
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接着跟进DispatchServlet的onRefresh方法，这个方法中会初始化DispatchServlet的九大策略，这里我们只关心initHandlerMappings方法
@Override
protected void onRefresh(ApplicationContext context) {
initStrategies(context);
}
//初始化策略
protected void initStrategies(ApplicationContext context) {
initMultipartResolver(context);
initLocaleResolver(context);
initThemeResolver(context);
//这个是我们关注的核心，Controller注册就在这里实现
initHandlerMappings(context);
//这个是处理Controller方法调用的，逻辑跟上面的initHandlerMappings差不多
initHandlerAdapters(context);
initHandlerExceptionResolvers(context);
initRequestToViewNameTranslator(context);
initViewResolvers(context);
initFlashMapManager(context);
}
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核心看下initHandlerMappings方法
private void initHandlerMappings(ApplicationContext context) {
this.handlerMappings = null;
//默认为true
if (this.detectAllHandlerMappings) {
//默认的HandlerMapping有8个，这里我们只关心RequestMappingHandlerMapping这个类
Map<String, HandlerMapping> matchingBeans =
BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false);
if (!matchingBeans.isEmpty()) {
this.handlerMappings = new ArrayList<>(matchingBeans.values());
//排序
AnnotationAwareOrderComparator.sort(this.handlerMappings);
}
}
else {
try {
HandlerMapping hm = context.getBean(HANDLER_MAPPING_BEAN_NAME, HandlerMapping.class);
//这里就让Serlvet和Controller建立起了间接关系了，这个方法主要是为了给handlerMappings属性赋值
this.handlerMappings = Collections.singletonList(hm);
}
catch (NoSuchBeanDefinitionException ex) {
}
}
//这里如果没有HanlderMapping的话，会给一个默认的处理
if (this.handlerMappings == null) {
this.handlerMappings = getDefaultStrategies(context, HandlerMapping.class);
if (logger.isTraceEnabled()) {
logger.trace("No HandlerMappings declared for servlet '" + getServletName() +
"': using default strategies from DispatcherServlet.properties");
}
}
}
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看下默认的 HandlerMapping 有哪些
这里我们只关心
RequestMappingHandlerMapping这个类，这个类就是处理我们Controller上的RequestMapping注解的类。
注意这里的handlerMappings，后面处理请求的时候，会从handlerMappings中选择一个最合适的HandlerMapping来处理请求
HttpServlet中的service方法源码
/**
* 这个方法只是将ServletRequest强转为HttpServletRequest
* ServletResponse强转为HttpServletResponse
*/
@Override
public void service(ServletRequest req, ServletResponse res)
throws ServletException, IOException {
HttpServletRequest request;
HttpServletResponse response;
try {
request = (HttpServletRequest) req;
response = (HttpServletResponse) res;
} catch (ClassCastException e) {
throw new ServletException(lStrings.getString("http.non_http"));
}
//接着看这个
service(request, response);
}
protected void service(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
//获取方法类型
String method = req.getMethod();
//根据不同的方法类型调用不同的方法，从doGet进去，看子类FrameworkServlet的doGet方法
if (method.equals(METHOD_GET)) {
long lastModified = getLastModified(req);
if (lastModified == -1) {
doGet(req, resp);
} else {
long ifModifiedSince;
try {
ifModifiedSince = req.getDateHeader(HEADER_IFMODSINCE);
} catch (IllegalArgumentException iae) {
ifModifiedSince = -1;
}
if (ifModifiedSince < (lastModified / 1000 * 1000)) {
maybeSetLastModified(resp, lastModified);
doGet(req, resp);
} else {
resp.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
}
}
} else if (method.equals(METHOD_HEAD)) {
long lastModified = getLastModified(req);
maybeSetLastModified(resp, lastModified);
doHead(req, resp);
} else if (method.equals(METHOD_POST)) {
doPost(req, resp);
} else if (method.equals(METHOD_PUT)) {
doPut(req, resp);
} else if (method.equals(METHOD_DELETE)) {
doDelete(req, resp);
} else if (method.equals(METHOD_OPTIONS)) {
doOptions(req,resp);
} else if (method.equals(METHOD_TRACE)) {
doTrace(req,resp);
} else {
String errMsg = lStrings.getString("http.method_not_implemented");
Object[] errArgs = new Object[1];
errArgs[0] = method;
errMsg = MessageFormat.format(errMsg, errArgs);
resp.sendError(HttpServletResponse.SC_NOT_IMPLEMENTED, errMsg);
}
}
//FrameworkServlet的doGet方法
@Override
protected final void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//继续跟
processRequest(request, response);
}
rotected 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 {
//这里处理请求，继续跟，看子类DispatchServlet的doService方法
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);
}
}
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@Override
protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
// 打印日志
logRequest(request);
//保存快照
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));
}
}
}
//设置属性
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 {
//处理请求核心方法
doDispatch(request, response);
}
finally {
if (!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
if (attributesSnapshot != null) {
restoreAttributesAfterInclude(request, attributesSnapshot);
}
}
}
}
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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);
// 获取当前请求的handler
mappedHandler = getHandler(processedRequest);
if (mappedHandler == null) {
//404
noHandlerFound(processedRequest, response);
return;
}
// 获取处理当前请求的handlerAdapter
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
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;
}
}
//调用前置拦截器
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
// 请求对应的方法在这里被执行
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
applyDefaultViewName(processedRequest, mv);
//调用后置拦截器
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);
}
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);
}
}
}
}
@Nullable
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
if (this.handlerMappings != null) {
for (HandlerMapping mapping : this.handlerMappings) {
//这里的mapping就是接下来要讲到的RequestMappingHandlerMapping
HandlerExecutionChain handler = mapping.getHandler(request);
if (handler != null) {
return handler;
}
}
}
return null;
}
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这里可以记录Servlet处理请求的调用链 service -> doGet -> processRequest -> doService -> doDispatch
从上面的继承图可以看出
RequestMappingHandlerMapping实现了InitializingBean接口，所以初始化的时候会调用afterPropertiesSet方法。
@Override
@SuppressWarnings("deprecation")
public void afterPropertiesSet() {
//配置
this.config = new RequestMappingInfo.BuilderConfiguration();
this.config.setUrlPathHelper(getUrlPathHelper());
this.config.setPathMatcher(getPathMatcher());
this.config.setSuffixPatternMatch(useSuffixPatternMatch());
this.config.setTrailingSlashMatch(useTrailingSlashMatch());
this.config.setRegisteredSuffixPatternMatch(useRegisteredSuffixPatternMatch());
this.config.setContentNegotiationManager(getContentNegotiationManager());
//这里是核心，会把所有controller注册进去
super.afterPropertiesSet();
}
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接着看父类
AbstractHandlerMethodMapping的afterPropertiesSet方法
@Override
public void afterPropertiesSet() {
initHandlerMethods();
}
protected void initHandlerMethods() {
for (String beanName : getCandidateBeanNames()) {
if (!beanName.startsWith(SCOPED_TARGET_NAME_PREFIX)) {
//这里会注册controller
processCandidateBean(beanName);
}
}
handlerMethodsInitialized(getHandlerMethods());
}
protected void processCandidateBean(String beanName) {
Class<?> beanType = null;
try {
beanType = obtainApplicationContext().getType(beanName);
}
catch (Throwable ex) {
if (logger.isTraceEnabled()) {
logger.trace("Could not resolve type for bean '" + beanName + "'", ex);
}
}
//这里的isHandler会判断是否有Controller或RequestMapping注解
if (beanType != null && isHandler(beanType)) {
//这里会注册controller，接着跟
detectHandlerMethods(beanName);
}
}
protected void detectHandlerMethods(Object handler) {
//获取类型
Class<?> handlerType = (handler instanceof String ?
obtainApplicationContext().getType((String) handler) : handler.getClass());
if (handlerType != null) {
Class<?> userType = ClassUtils.getUserClass(handlerType);
Map<Method, T> methods = MethodIntrospector.selectMethods(userType,
(MethodIntrospector.MetadataLookup<T>) method -> {
try {
//这里会把RequestMapping转换为RequestMappingInfo
return getMappingForMethod(method, userType);
}
catch (Throwable ex) {
throw new IllegalStateException("Invalid mapping on handler class [" +
userType.getName() + "]: " + method, ex);
}
});
if (logger.isTraceEnabled()) {
logger.trace(formatMappings(userType, methods));
}
methods.forEach((method, mapping) -> {
Method invocableMethod = AopUtils.selectInvocableMethod(method, userType);
//注册到mappingRegistry中，后面会根据request获取对应的HandlerMethod
registerHandlerMethod(handler, invocableMethod, mapping);
});
}
}
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RequestMapping转换为RequestMappingInfo
@Override
@Nullable
protected RequestMappingInfo getMappingForMethod(Method method, Class<?> handlerType) {
//获取方法上的RequestMapping并且转换为RequestMappingInfo
RequestMappingInfo info = createRequestMappingInfo(method);
if (info != null) {
//获取类上的RequestMapping并且转换为RequestMappingInfo（这里就是Controller上的RequestMapping）
RequestMappingInfo typeInfo = createRequestMappingInfo(handlerType);
if (typeInfo != null) {
//将方法上的RequestMapping和类上的RequestMapping合并，这里会合并url
info = typeInfo.combine(info);
}
String prefix = getPathPrefix(handlerType);
if (prefix != null) {
info = RequestMappingInfo.paths(prefix).options(this.config).build().combine(info);
}
}
return info;
}
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这个方法会把方法上的RequestMapping转换为RequestMappingInfo，把类上的RequestMapping转换为RequestMappingInfo，然后再把两个RequestMappingInfo合并成一个（url的合并）。
protected void registerHandlerMethod(Object handler, Method method, T mapping) {
//这里直接注册到mappingRegistry中，后面也直接从mappingRegistry获取
this.mappingRegistry.register(mapping, handler, method);
}
public void register(T mapping, Object handler, Method method) {
if (KotlinDetector.isKotlinType(method.getDeclaringClass())) {
Class<?>[] parameterTypes = method.getParameterTypes();
if ((parameterTypes.length > 0) && "kotlin.coroutines.Continuation".equals(parameterTypes[parameterTypes.length - 1].getName())) {
throw new IllegalStateException("Unsupported suspending handler method detected: " + method);
}
}
this.readWriteLock.writeLock().lock();
try {
//创建HandlerMethod
HandlerMethod handlerMethod = createHandlerMethod(handler, method);
validateMethodMapping(handlerMethod, mapping);
this.mappingLookup.put(mapping, handlerMethod);
List<String> directUrls = getDirectUrls(mapping);
for (String url : directUrls) {
this.urlLookup.add(url, mapping);
}
String name = null;
if (getNamingStrategy() != null) {
name = getNamingStrategy().getName(handlerMethod, mapping);
addMappingName(name, handlerMethod);
}
CorsConfiguration corsConfig = initCorsConfiguration(handler, method, mapping);
if (corsConfig != null) {
this.corsLookup.put(handlerMethod, corsConfig);
}
//这里会添加到MappingRegistry中去
this.registry.put(mapping, new MappingRegistration<>(mapping, handlerMethod, directUrls, name));
}
finally {
this.readWriteLock.writeLock().unlock();
}
}
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这里需要注意的是，注册的Controller是直接注册的HandlerMethod，这个HandlerMethod就是对应的Controller类中具体请求对应的方法，这个对象封装了所有信息，后面获取出HandlerMethod后会通过反射调用具体的方法
进入
RequestMappingHandlerMapping的getHandler方法看下，这个方法在父类AbstractHandlerMapping中实现，这里用到了设计模式中的模版方法。
@Override
@Nullable
public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
//这里获取真正的处理器，子类AbstractHandlerMethodMapping实现
Object handler = getHandlerInternal(request);
if (handler == null) {
//没有的话，使用默认的
handler = getDefaultHandler();
}
if (handler == null) {
return null;
}
// 如果是beanName的话 从ioc容器中获取真正的实例
if (handler instanceof String) {
String handlerName = (String) handler;
handler = obtainApplicationContext().getBean(handlerName);
}
//这里获取对应请求的拦截器链
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;
}
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这里核心关注两个方法，一个是获取处理器的getHandlerInternal方法，一个是获取对应拦截器链的getHandlerExecutionChain方法
@Override
protected HandlerMethod getHandlerInternal(HttpServletRequest request) throws Exception {
String lookupPath = getUrlPathHelper().getLookupPathForRequest(request);
request.setAttribute(LOOKUP_PATH, lookupPath);
this.mappingRegistry.acquireReadLock();
try {
HandlerMethod handlerMethod = lookupHandlerMethod(lookupPath, request);
return (handlerMethod != null ? handlerMethod.createWithResolvedBean() : null);
}
finally {
this.mappingRegistry.releaseReadLock();
}
}
@Nullable
protected HandlerMethod lookupHandlerMethod(String lookupPath, HttpServletRequest request) throws Exception {
List<Match> matches = new ArrayList<>();
List<T> directPathMatches = this.mappingRegistry.getMappingsByUrl(lookupPath);
if (directPathMatches != null) {
addMatchingMappings(directPathMatches, matches, request);
}
if (matches.isEmpty()) {
// No choice but to go through all mappings...
addMatchingMappings(this.mappingRegistry.getMappings().keySet(), matches, request);
}
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;
}
else {
return handleNoMatch(this.mappingRegistry.getMappings().keySet(), lookupPath, request);
}
}
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从上面的方法中可以看出，最后是从mappingRegistry属性中取出的HandlerMethod，mappingRegistry在上面的
RequestMappingHandlerMapping中有详细讲解
protected HandlerExecutionChain getHandlerExecutionChain(Object handler, HttpServletRequest request) {
HandlerExecutionChain chain = (handler instanceof HandlerExecutionChain ?
(HandlerExecutionChain) handler : new HandlerExecutionChain(handler));
//这里会拿到所有的拦截器，然后通过路径匹配到合适的拦截器
String lookupPath = this.urlPathHelper.getLookupPathForRequest(request, LOOKUP_PATH);
for (HandlerInterceptor interceptor : this.adaptedInterceptors) {
if (interceptor instanceof MappedInterceptor) {
MappedInterceptor mappedInterceptor = (MappedInterceptor) interceptor;
if (mappedInterceptor.matches(lookupPath, this.pathMatcher)) {
chain.addInterceptor(mappedInterceptor.getInterceptor());
}
}
else {
chain.addInterceptor(interceptor);
}
}
return chain;
}
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到这就已经拿到了对应的拦截器链和响应请求对应的方法了。接下来就是调用方法了，这里就轮到HandlerAdapter出场了，如何获取
RequestMappingHandlerAdapter的方法getHandlerAdapter这里就跳过了
再回到DispatchServlet的doDispatch方法中的
//这里的ha就是RequestMappingHandlerAdapter类
//核心是RequestMappingHandlerAdapter类的handleInternal方法
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
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@Override
protected ModelAndView handleInternal(HttpServletRequest request,
HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
ModelAndView mav;
checkRequest(request);
if (this.synchronizeOnSession) {
HttpSession session = request.getSession(false);
if (session != null) {
Object mutex = WebUtils.getSessionMutex(session);
synchronized (mutex) {
//这里就是真正调用HandlerMethod的地方了
mav = invokeHandlerMethod(request, response, handlerMethod);
}
}
else {
//这里就是真正调用HandlerMethod的地方了
mav = invokeHandlerMethod(request, response, handlerMethod);
}
}
else {
//这里就是真正调用HandlerMethod的地方了
mav = invokeHandlerMethod(request, response, handlerMethod);
}
if (!response.containsHeader(HEADER_CACHE_CONTROL)) {
if (getSessionAttributesHandler(handlerMethod).hasSessionAttributes()) {
applyCacheSeconds(response, this.cacheSecondsForSessionAttributeHandlers);
}
else {
prepareResponse(response);
}
}
return mav;
}
复制代码
到这里，整个调用的过程就已经到此为止了。其中的HandlerAdapter的注册、获取、处理请求反射调用HandlerMethod等以后的章节再分析。
链接：
https://juejin.cn/post/7026266185729572872
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