SpringMVC源码-DispatcherServlet处理请求概述
请求由Servlet的Service()处理。
FrameworkServlet.service(HttpServletRequest request, HttpServletResponse response)
protected void service(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
HttpMethod httpMethod = HttpMethod.resolve(request.getMethod());
if (httpMethod == HttpMethod.PATCH || httpMethod == null) {
processRequest(request, response);
}
else {
super.service(request, response);
}
}
如果请求方法是patch调用processRequest，否则调用super.service。
HttpServlet.service(HttpServletRequest req, HttpServletResponse resp)
protected void service(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException
{
String method = req.getMethod();
if (method.equals(METHOD_GET)) {
long lastModified = getLastModified(req);
if (lastModified == -1) {
// servlet doesn't support if-modified-since, no reason
// to go through further expensive logic
doGet(req, resp);
} else {
long ifModifiedSince = req.getDateHeader(HEADER_IFMODSINCE);
if (ifModifiedSince < lastModified) {
// 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
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 {
//
// Note that this means NO servlet supports whatever
// method was requested, anywhere on this server.
//
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);
}
}
如果请求方法是get调用doGet，head方法调用doHead，post方法调用doPost，put方法调用doPut，delete方法调用doDelete，options方法调用doOptions，trace方法调用doTrace，若不是上面的方法则设置错误。
FrameworkServlet.doGet(HttpServletRequest request, HttpServletResponse response)
protected final void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
processRequest(request, response);
}
HttpServlet.doHead(HttpServletRequest req, HttpServletResponse resp)
protected void doHead(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException
{
NoBodyResponse response = new NoBodyResponse(resp);
doGet(req, response);
response.setContentLength();
}
head处理方法调用doGet，response设置ContentLength。
FrameworkServlet.doPost(HttpServletRequest request, HttpServletResponse response)
protected final void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
processRequest(request, response);
}
FrameworkServlet.doPut(HttpServletRequest request, HttpServletResponse response)
protected final void doPut(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
processRequest(request, response);
}
FrameworkServlet.doDelete(HttpServletRequest request, HttpServletResponse response)
protected final void doDelete(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
processRequest(request, response);
}
FrameworkServlet.doOptions(HttpServletRequest request, HttpServletResponse response)
protected void doOptions(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
if (this.dispatchOptionsRequest || CorsUtils.isPreFlightRequest(request)) {
processRequest(request, response);
if (response.containsHeader("Allow")) {
// Proper OPTIONS response coming from a handler - we're done.
return;
}
}
// Use response wrapper in order to always add PATCH to the allowed methods
super.doOptions(request, new HttpServletResponseWrapper(response) {
@Override
public void setHeader(String name, String value) {
if ("Allow".equals(name)) {
value = (StringUtils.hasLength(value) ? value + ", " : "") + HttpMethod.PATCH.name();
}
super.setHeader(name, value);
}
});
}
如果dispatchOptionsRequest为true或CorsUtils.isPreFlightRequest检查header是否有CROS头部为true，则调用processRequest。super.doOptions设置Allow header。
FrameworkServlet.doTrace(HttpServletRequest request, HttpServletResponse response)
protected void doTrace(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
if (this.dispatchTraceRequest) {
processRequest(request, response);
if ("message/http".equals(response.getContentType())) {
// Proper TRACE response coming from a handler - we're done.
return;
}
}
super.doTrace(request, response);
}
如果dispatchTraceRequest为true，调用processRequest。super.doTrace设置头部。
FrameworkServlet.dispatchTraceRequest
protected 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 {
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);
}
}
1、创建LocaleContext
2、创建ServletRequestAttributes请求属性
3、创建WebAsyncManager
4、WebAsyncManager将RequestBindingInterceptor注册到CallableInterceptor。
5、initContextHolders设置请求属性
6、调用doService
7、恢复LocaleContext和ServletRequestAttributes
8、发布ServletRequestHandledEvent事件
DispatcherServlet.doService(HttpServletRequest request, HttpServletResponse response)
protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
logRequest(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;
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);
}
RequestPath previousRequestPath = null;
if (this.parseRequestPath) {
previousRequestPath = (RequestPath) request.getAttribute(ServletRequestPathUtils.PATH_ATTRIBUTE);
ServletRequestPathUtils.parseAndCache(request);
}
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);
}
}
ServletRequestPathUtils.setParsedRequestPath(previousRequestPath, request);
}
}
1、logRequest返回request的参数字符串供日志打印。
2、对request的属性做快照
3、request设置属性WEB_APPLICATION_CONTEXT_ATTRIBUTE为WebApplicationContext，设置属性LOCALE_RESOLVER_ATTRIBUTE为localeResolver，设置属性THEME_RESOLVER_ATTRIBUTE为themeResolver，设置属性THEME_SOURCE_ATTRIBUTE为ThemeSource。
4、如果flashMapManager不为null，flashMapManager.retrieveAndUpdate保存以前的FlashMap，匹配当前请求的FlashMap并返回，inputFlashMap不为null设置INPUT_FLASH_MAP_ATTRIBUTE为名，inputFlashMap为值的属性。设置OUTPUT_FLASH_MAP_ATTRIBUTE和FLASH_MAP_MANAGER_ATTRIBUTE属性。
5、如果parseRequestPath为true，解析request的PATH_ATTRIBUTE属性值并缓存。
6、doDispatch分发请求进行处理
7、还原request的属性快照
DispatcherServlet.doDispatch(HttpServletRequest request, HttpServletResponse response)
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) {
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 (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);
}
}
}
}
1、WebAsyncUtils.getAsyncManager获取异步web管理器WebAsyncManager
2、checkMultipart检查是否是文件上传请求
3、调用getHandler获取request的handle
4、如果没有当前请求的handle则调用noHandlerFound
5、调用getHandlerAdapter获取handle对应的HandlerAdapter
6、如果请求类型是GET或HEAD则检查请求的lastModified
7、调用mappedHandler.applyPreHandle处理拦截器的前置方法HandlerInterceptor.preHandle,如果为false则退出
8、HandlerAdapter.handle调用Controller层的方法处理请求并返回ModelAndView
9、applyDefaultViewName处理视图名
10、mappedHandler.applyPostHandle处理拦截器的前置方法HandlerInterceptor.postHandle
11、processDispatchResult渲染视图
12、如果是异步web调用mappedHandler.applyAfterConcurrentHandlingStarted否则cleanupMultipart清理文件上传请求
DispatcherServlet.checkMultipart(HttpServletRequest request)
protected HttpServletRequest checkMultipart(HttpServletRequest request) throws MultipartException {
if (this.multipartResolver != null && this.multipartResolver.isMultipart(request)) {
if (WebUtils.getNativeRequest(request, MultipartHttpServletRequest.class) != null) {
if (DispatcherType.REQUEST.equals(request.getDispatcherType())) {
logger.trace("Request already resolved to MultipartHttpServletRequest, e.g. by MultipartFilter");
}
}
else if (hasMultipartException(request)) {
logger.debug("Multipart resolution previously failed for current request - " +
"skipping re-resolution for undisturbed error rendering");
}
else {
try {
return this.multipartResolver.resolveMultipart(request);
}
catch (MultipartException ex) {
if (request.getAttribute(WebUtils.ERROR_EXCEPTION_ATTRIBUTE) != null) {
logger.debug("Multipart resolution failed for error dispatch", ex);
// Keep processing error dispatch with regular request handle below
}
else {
throw ex;
}
}
}
}
// If not returned before: return original request.
return request;
}
如果multipartResolver不为null且multipartResolver.isMultipart判断request是文件上传请求则
1、WebUtils.getNativeRequest判断request是MultipartHttpServletRequest，若是且request.getDispatcherType()是DispatcherType.REQUEST打印日志
2、hasMultipartException判断是否有异常，若有打印日志
3、调用multipartResolver.resolveMultipart解析request并返回
