一些重要的類

HandlerExecutionChain

用于保存Controller中的方法和對(duì)應(yīng)的HandlerInterceptor對(duì)象

image.png

分配請(qǐng)求過(guò)程

java web HttpServlet提供了service方法用于處理請(qǐng)求，service使用了模板設(shè)計(jì)模式，在內(nèi)部對(duì)于httpget方法會(huì)調(diào)用doGet方法，httppost方法調(diào)用doPost方法...

這些方法在FrameworkServlet里均會(huì)調(diào)用processRequest方法，這個(gè)方法定義如下

protected final void processRequest(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {

long startTime = System.currentTimeMillis();
Throwable failureCause = null;

//進(jìn)行請(qǐng)求線程和LocaleContext,ServletRequestAttributes綁定
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 {
//抽象方法，實(shí)際定義在子類DispatcherServlet中
doService(request, response);
}
catch (ServletException ex) {
failureCause = ex;
throw ex;
}
catch (IOException ex) {
failureCause = ex;
throw ex;
}
catch (Throwable ex) {
failureCause = ex;
throw new NestedServletException("Request processing failed", ex);
}

finally {
//解除請(qǐng)求線程和LocaleContext,ServletRequestAttributes綁定
resetContextHolders(request, previousLocaleContext, previousAttributes);
if (requestAttributes != null) {
requestAttributes.requestCompleted();
}

if (logger.isDebugEnabled()) {
if (failureCause != null) {
this.logger.debug("Could not complete request", failureCause);
}
else {
if (asyncManager.isConcurrentHandlingStarted()) {
logger.debug("Leaving response open for concurrent processing");
}
else {
this.logger.debug("Successfully completed request");
}
}
}

publishRequestHandledEvent(request, response, startTime, failureCause);
}
}

可以看到核心方法是調(diào)用 doService，這個(gè)方法定義在DispatcherServlet中

@Override
protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
if (logger.isDebugEnabled()) {
String resumed = WebAsyncUtils.getAsyncManager(request).hasConcurrentResult() ? " resumed" : "";
logger.debug("DispatcherServlet with name '" + getServletName() + "'" + resumed +
" processing " + request.getMethod() + " request for [" + getRequestUri(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;
//如果是include請(qǐng)求，保存一份request的中的數(shù)據(jù)
if (WebUtils.isIncludeRequest(request)) {
attributesSnapshot = new HashMap<>();
Enumeration<?> attrNames = request.getAttributeNames();
while (attrNames.hasMoreElements()) {
String attrName = (String) attrNames.nextElement();
if (this.cleanupAfterInclude || attrName.startsWith("org.springframework.web.servlet")) {
attributesSnapshot.put(attrName, request.getAttribute(attrName));
}
}
}

// Make framework objects available to handlers and view objects.
//request設(shè)置一些屬性
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());

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 {
//進(jìn)行分發(fā)處理
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);
}
}
}
}

核心方法是調(diào)用doDispatch

核心方法 doDispatch如下

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.
mappedHandler = getHandler(processedRequest);
if (mappedHandler == null || mappedHandler.getHandler() == null) {
noHandlerFound(processedRequest, response);
return;
}

// Determine handler adapter for the current request.
HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

// Process last-modified header, if supported by the handler.
String method = request.getMethod();
boolean isGet = "GET".equals(method);
if (isGet || "HEAD".equals(method)) {
long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
if (logger.isDebugEnabled()) {
logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified);
}
if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
return;
}
}

if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}

// Actually invoke the handler.
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

if (asyncManager.isConcurrentHandlingStarted()) {
return;
}

applyDefaultViewName(processedRequest, mv);
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);
}
}
}
}

調(diào)用doDispatch后發(fā)生事大致可以概括為：

• 構(gòu)造HandlerExecutionChain，根據(jù)請(qǐng)求的路徑找到HandlerMethod(帶有Method反射屬性，也就是對(duì)應(yīng)Controller中的方法)，然后匹配路徑對(duì)應(yīng)的攔截器，有了HandlerMethod和攔截器構(gòu)造個(gè)HandlerExecutionChain對(duì)象。HandlerExecutionChain對(duì)象的獲取是通過(guò)HandlerMapping接口提供的方法中得到。

• 構(gòu)造HandlerAdapter,有了HandlerExecutionChain之后，通過(guò)HandlerAdapter對(duì)象進(jìn)行處理得到ModelAndView對(duì)象，HandlerMethod內(nèi)部handle的時(shí)候，使用各種HandlerMethodArgumentResolver實(shí)現(xiàn)類處理HandlerMethod的參數(shù)，使用各種HandlerMethodReturnValueHandler實(shí)現(xiàn)類處理返回值。 最終返回值被處理成ModelAndView對(duì)象，這期間發(fā)生的異常會(huì)被HandlerExceptionResolver接口實(shí)現(xiàn)類進(jìn)行處理

首先看獲取HandlerExecutionChain的函數(shù) getHandler

protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
for (HandlerMapping hm : this.handlerMappings) {
if (logger.isTraceEnabled()) {
logger.trace(
"Testing handler map [" + hm + "] in DispatcherServlet with name '" + getServletName() + "'");
}
HandlerExecutionChain handler = hm.getHandler(request);
if (handler != null) {
return handler;
}
}
return null;
}

就是調(diào)用了HandlerMapping方法，我們已經(jīng)知道，一般情況下，handlerMappings這個(gè) 數(shù)據(jù)成員里存的是RequestMappingHandlerMapping的一個(gè)實(shí)例，也就是通過(guò)RequestMappingHandlerMapping.getHandler獲取了這個(gè)執(zhí)行序列