HttpServlet#service
protected void service(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
//擷取請求類型
String method = req.getMethod();
//如果是get請求
if (method.equals(METHOD_GET)) {
//檢查是不是開啟了頁面緩存 通過header頭的 Last-Modified/If-Modified-Since
//擷取Last-Modified的值
long lastModified = getLastModified(req);
if (lastModified == -1) {
// servlet doesn't support if-modified-since, no reason
// to go through further expensive logic
//沒有開啟頁面緩存調用doGet方法
doGet(req, resp);
} else {
long ifModifiedSince;
try {
//擷取If-Modified-Since的值
ifModifiedSince = req.getDateHeader(HEADER_IFMODSINCE);
} catch (IllegalArgumentException iae) {
ifModifiedSince = -1;
}
if (ifModifiedSince < (lastModified / 1000 * 1000)) {
// If the servlet mod time is later, call doGet()
// Round down to the nearest second for a proper compare
// A ifModifiedSince of -1 will always be less
//更新Last-Modified
maybeSetLastModified(resp, lastModified);
//調用doGet方法
doGet(req, resp);
} else {
//設定304狀态碼 在HttpServletResponse中定義了很多常用的狀态碼
resp.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
}
}
} else if (method.equals(METHOD_HEAD)) {
//調用doHead方法
long lastModified = getLastModified(req);
maybeSetLastModified(resp, lastModified);
doHead(req, resp);
} else if (method.equals(METHOD_POST)) {
//調用doPost方法
doPost(req, resp);
} else if (method.equals(METHOD_PUT)) {
//調用doPost方法
doPut(req, resp);
} else if (method.equals(METHOD_DELETE)) {
//調用doPost方法
doDelete(req, resp);
} else if (method.equals(METHOD_OPTIONS)) {
//調用doPost方法
doOptions(req,resp);
} else if (method.equals(METHOD_TRACE)) {
//調用doPost方法
doTrace(req,resp);
} else {
//伺服器不支援的方法 直接傳回錯誤資訊
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);
}
} 根據請求類型調用響應的請求方法如果GET類型，調用doGet方法
POST類型，調用doPost方法。
這些方法都是在HttpServlet中定義的，平時我們做web開發的時候主要是繼承HttpServlet這個類，然後重寫它的doPost或者doGet方法。
我們的FrameworkServlet這個子類就重寫了這些方法中的一部分：doGet、doPost、doPut、doDelete、doOption、doTrace。
這裡我們隻說我們最常用的doGet和doPost這兩個方法。通過翻開源碼我們發現，這兩個方法體的内容是一樣的，都是調用了processRequest
FrameworkServlet#processRequest
protected final void processRequest(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
long startTime = System.currentTimeMillis();
Throwable failureCause = null;
LocaleContext previousLocaleContext = LocaleContextHolder.getLocaleContext();
//國際化
LocaleContext localeContext = buildLocaleContext(request);
RequestAttributes previousAttributes = RequestContextHolder.getRequestAttributes();
//建構ServletRequestAttributes對象
ServletRequestAttributes requestAttributes = buildRequestAttributes(request, response, previousAttributes);
//異步管理
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
asyncManager.registerCallableInterceptor(FrameworkServlet.class.getName(), new RequestBindingInterceptor());
//初始化ContextHolders
initContextHolders(request, localeContext, requestAttributes);
//執行doService
try {
doService(request, response);
}
finally {
//重新設定ContextHolders
resetContextHolders(request, previousLocaleContext, previousAttributes);
if (requestAttributes != null) {
requestAttributes.requestCompleted();
}
//釋出請求處理事件
publishRequestHandledEvent(request, response, startTime, failureCause);
}
} 國際化的設定，建立ServletRequestAttributes對象，初始化上下文holders(即将Request對象放入到線程上下文中)，調用doService方法。
國際化的設定
DispatcherServlet#buildLocaleContext這個方法中完成的，其源碼如下：
protected LocaleContext buildLocaleContext(final HttpServletRequest request) {
if (this.localeResolver instanceof LocaleContextResolver) {
return ((LocaleContextResolver) this.localeResolver).resolveLocaleContext(request);
}
else {
return new LocaleContext() {
@Override
public Locale getLocale() {
return localeResolver.resolveLocale(request);
}
};
}
} 沒有配置國際化解析器的話，那麼它會使用預設的解析器：AcceptHeaderLocaleResolver，即從Header中擷取國際化的資訊。
除了AcceptHeaderLocaleResolver之外，SpringMVC中還提供了這樣的幾種解析器：CookieLocaleResolver、SessionLocaleResolver、FixedLocaleResolver。分别從cookie、session中去國際化資訊和JVM預設的國際化資訊(Local.getDefault())。
initContextHolders這個方法主要是将Request請求、ServletRequestAttribute對象和國際化對象放入到上下文中。其源碼如下：
private void initContextHolders(
HttpServletRequest request, LocaleContext localeContext, RequestAttributes requestAttributes) {
if (localeContext != null) {
LocaleContextHolder.setLocaleContext(localeContext, this.threadContextInheritable);//threadContextInheritable預設為false
}
if (requestAttributes != null) {//threadContextInheritable預設為false
RequestContextHolder.setRequestAttributes(requestAttributes, this.threadContextInheritable);
}
} RequestContextHolder這個類有什麼用呢？有時候我們想在某些類中擷取HttpServletRequest對象，比如在AOP攔截的類中，那麼我們就可以這樣來擷取Request的對象了，
HttpServletRequest request = (HttpServletRequest) RequestContextHolder.getRequestAttributes().resolveReference(RequestAttributes.REFERENCE_REQUEST); DispatcherServlet#doService
@Override
protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
Map<String, Object> attributesSnapshot = null;
if (WebUtils.isIncludeRequest(request)) {
attributesSnapshot = new HashMap<String, Object>();
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));
}
}
}
//Spring上下文
request.setAttribute(WEB_APPLICATION_CONTEXT_ATTRIBUTE, getWebApplicationContext());
//國際化解析器
request.setAttribute(LOCALE_RESOLVER_ATTRIBUTE, this.localeResolver);
//主題解析器
request.setAttribute(THEME_RESOLVER_ATTRIBUTE, this.themeResolver);
//主題
request.setAttribute(THEME_SOURCE_ATTRIBUTE, getThemeSource());
//重定向的資料
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 {
//調用doDispatch方法-核心方法
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);
}
}
}
} 處理include标簽的請求，将上下文放到request的屬性中，将國際化解析器放到request的屬性中，将主題解析器放到request屬性中，将主題放到request的屬性中，處理重定向的請求資料最後調用doDispatch這個核心的方法對請求進行處理
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