SpringMVC的DispatcherServlet处理请求的流程
内容参考https://my.oschina.net/lichhao/blog/104943
SpringMVC请求的大致处理流程图
1、请求的入口
1.1、HttpServlet与FrameworkServlet
从设计上看，SpringMVC是依托Servlet容器来设计的。在SpringMVC初始化之后，同样通过service()方法来接受、处理、返回。
DispatcherServlet的service()方法是他的父类FrameworkServlet实现的。
protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
HttpMethod httpMethod = HttpMethod.resolve(request.getMethod());
if (httpMethod != HttpMethod.PATCH && httpMethod != null) {
super.service(request, response);
} else {
// 最终会调用此方法
this.processRequest(request, response);
}
}protected final void processRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
long startTime = System.currentTimeMillis();
Throwable failureCause = null;
LocaleContext previousLocaleContext = LocaleContextHolder.getLocaleContext();
LocaleContext localeContext = this.buildLocaleContext(request);
RequestAttributes previousAttributes = RequestContextHolder.getRequestAttributes();
ServletRequestAttributes requestAttributes = this.buildRequestAttributes(request, response, previousAttributes);
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
asyncManager.registerCallableInterceptor(FrameworkServlet.class.getName(), new FrameworkServlet.RequestBindingInterceptor());
this.initContextHolders(request, localeContext, requestAttributes);
try {
//doService（）是抽象方法，调用的就是DispatcherServlet的doService方法
this.doService(request, response);
} catch (IOException | ServletException var16) {
failureCause = var16;
throw var16;
} catch (Throwable var17) {
failureCause = var17;
throw new NestedServletException("Request processing failed", var17);
} finally {
this.resetContextHolders(request, previousLocaleContext, previousAttributes);
if (requestAttributes != null) {
requestAttributes.requestCompleted();
}
this.logResult(request, response, (Throwable)failureCause, asyncManager);
this.publishRequestHandledEvent(request, response, startTime, (Throwable)failureCause);
}
}1.2、DispatcherServlet的doService(HttpServletRequest request, HttpServletResponse response)方法
protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
this.logRequest(request);
Map attributesSnapshot = null;
if (WebUtils.isIncludeRequest(request)) {
attributesSnapshot = new HashMap();
Enumeration attrNames = request.getAttributeNames();
label95:
while(true) {
String attrName;
do {
if (!attrNames.hasMoreElements()) {
break label95;
}
attrName = (String)attrNames.nextElement();
} while(!this.cleanupAfterInclude && !attrName.startsWith("org.springframework.web.servlet"));
attributesSnapshot.put(attrName, request.getAttribute(attrName));
}
}
request.setAttribute(WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.getWebApplicationContext());
request.setAttribute(LOCALE_RESOLVER_ATTRIBUTE, this.localeResolver);
request.setAttribute(THEME_RESOLVER_ATTRIBUTE, this.themeResolver);
request.setAttribute(THEME_SOURCE_ATTRIBUTE, this.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 {
//为request设置各种属性，之后真正的业务请求处理在doDispatch中
this.doDispatch(request, response);
} finally {
if (!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted() && attributesSnapshot != null) {
this.restoreAttributesAfterInclude(request, attributesSnapshot);
}
}
} 在doDispatch()方法中，改出现的MVC设计终于尽收眼底。ModelAndView、HandlerExecutionChain、HandleAdapter、HandlerInterceptor等各司其职。这其中HandlerExecutionChain尤为重要，是带有主角光环的
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;
Object dispatchException = null;
try {
processedRequest = this.checkMultipart(request);
multipartRequestParsed = processedRequest != request;
mappedHandler = this.getHandler(processedRequest);
if (mappedHandler == null) {
this.noHandlerFound(processedRequest, response);
return;
}
HandlerAdapter ha = this.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;
}
}
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
this.applyDefaultViewName(processedRequest, mv);
mappedHandler.applyPostHandle(processedRequest, response, mv);
} catch (Exception var20) {
dispatchException = var20;
} catch (Throwable var21) {
dispatchException = new NestedServletException("Handler dispatch failed", var21);
}
this.processDispatchResult(processedRequest, response, mappedHandler, mv, (Exception)dispatchException);
} catch (Exception var22) {
this.triggerAfterCompletion(processedRequest, response, mappedHandler, var22);
} catch (Throwable var23) {
this.triggerAfterCompletion(processedRequest, response, mappedHandler, new NestedServletException("Handler processing failed", var23));
} finally {
if (asyncManager.isConcurrentHandlingStarted()) {
if (mappedHandler != null) {
mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
}
} else if (multipartRequestParsed) {
this.cleanupMultipart(processedRequest);
}
}
}HandlerExecutionChain.java
public class HandlerExecutionChain {
private static final Log logger = LogFactory.getLog(HandlerExecutionChain.class);
//handler对象
private final Object handler;
//拦截器链，可以在handler执行前后调用。类似AOP环绕通知一样
@Nullable
private HandlerInterceptor[] interceptors;
@Nullable
private List interceptorList;
private int interceptorIndex;
public HandlerExecutionChain(Object handler) {
this(handler, (HandlerInterceptor[])null);
}
public HandlerExecutionChain(Object handler, @Nullable HandlerInterceptor... interceptors) {
this.interceptorIndex = -1;
if (handler instanceof HandlerExecutionChain) {
HandlerExecutionChain originalChain = (HandlerExecutionChain)handler;
this.handler = originalChain.getHandler();
this.interceptorList = new ArrayList();
CollectionUtils.mergeArrayIntoCollection(originalChain.getInterceptors(), this.interceptorList);
CollectionUtils.mergeArrayIntoCollection(interceptors, this.interceptorList);
} else {
this.handler = handler;
this.interceptors = interceptors;
}
}
public Object getHandler() {
return this.handler;
}
public void addInterceptor(HandlerInterceptor interceptor) {
this.initInterceptorList().add(interceptor);
}
public void addInterceptor(int index, HandlerInterceptor interceptor) {
this.initInterceptorList().add(index, interceptor);
}
public void addInterceptors(HandlerInterceptor... interceptors) {
if (!ObjectUtils.isEmpty(interceptors)) {
CollectionUtils.mergeArrayIntoCollection(interceptors, this.initInterceptorList());
}
}
private List initInterceptorList() {
if (this.interceptorList == null) {
this.interceptorList = new ArrayList();
if (this.interceptors != null) {
CollectionUtils.mergeArrayIntoCollection(this.interceptors, this.interceptorList);
}
}
this.interceptors = null;
return this.interceptorList;
}
@Nullable
public HandlerInterceptor[] getInterceptors() {
if (this.interceptors == null && this.interceptorList != null) {
this.interceptors = (HandlerInterceptor[])this.interceptorList.toArray(new HandlerInterceptor[0]);
}
return this.interceptors;
}
boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {
HandlerInterceptor[] interceptors = this.getInterceptors();
if (!ObjectUtils.isEmpty(interceptors)) {
for(int i = 0; i < interceptors.length; this.interceptorIndex = i++) {
HandlerInterceptor interceptor = interceptors[i];
if (!interceptor.preHandle(request, response, this.handler)) {
this.triggerAfterCompletion(request, response, (Exception)null);
return false;
}
}
}
return true;
}
void applyPostHandle(HttpServletRequest request, HttpServletResponse response, @Nullable ModelAndView mv) throws Exception {
HandlerInterceptor[] interceptors = this.getInterceptors();
if (!ObjectUtils.isEmpty(interceptors)) {
for(int i = interceptors.length - 1; i >= 0; --i) {
HandlerInterceptor interceptor = interceptors[i];
interceptor.postHandle(request, response, this.handler, mv);
}
}
}
void triggerAfterCompletion(HttpServletRequest request, HttpServletResponse response, @Nullable Exception ex) throws Exception {
HandlerInterceptor[] interceptors = this.getInterceptors();
if (!ObjectUtils.isEmpty(interceptors)) {
for(int i = this.interceptorIndex; i >= 0; --i) {
HandlerInterceptor interceptor = interceptors[i];
try {
interceptor.afterCompletion(request, response, this.handler, ex);
} catch (Throwable var8) {
logger.error("HandlerInterceptor.afterCompletion threw exception", var8);
}
}
}
}
void applyAfterConcurrentHandlingStarted(HttpServletRequest request, HttpServletResponse response) {
HandlerInterceptor[] interceptors = this.getInterceptors();
if (!ObjectUtils.isEmpty(interceptors)) {
for(int i = interceptors.length - 1; i >= 0; --i) {
if (interceptors[i] instanceof AsyncHandlerInterceptor) {
try {
AsyncHandlerInterceptor asyncInterceptor = (AsyncHandlerInterceptor)interceptors[i];
asyncInterceptor.afterConcurrentHandlingStarted(request, response, this.handler);
} catch (Throwable var6) {
logger.error("Interceptor [" + interceptors[i] + "] failed in afterConcurrentHandlingStarted", var6);
}
}
}
}
}
}