引言
之前我们都是从一些官方文档或者是博客中了解了springMVC的整个处理流程,并且在前面博客我们也自己动手模拟了一个简单的springMVC容器,那么今天我们就对照流程图从源码分析一下S pringMVC的核心处理流程。
一、SpringMVC处理流程图
这张图已经非常清楚的画除了整个SpringMVC的处理流程,里面还写出了每个处理环节当中的类,当然如果没有 分析过源码,那么上面的图看起来会非常的乱。尤其是里面的一些核心类,所以如果想很愉快的欣赏上面的 流程图,就需要我们看过几遍源码。
二、DispatcherServlet 核心处理流程
DispatcherServlet 其实就是一个普通的servlet,所以当一个请求来到servlet的时候,肯定首先会进入service()方法,所以我们的入口方法肯定是service()方法:
进入DispatcherServlet方法:
public class DispatcherServlet extends FrameworkServlet
我们在DispatcherServlet方法中我们没有发现service方法,所以肯定在父类的FrameworkServlet类中
@Override
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);
}
}
从上面代码中我们会发现它继续调用了父类的service方法,所以我们继续进入到HttpServlet类中,在这个类中会见到我们非常熟悉的代码,也就是处理我们常见的几种处理方法:GET HEAD DELETE POST PUT等。
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);
}
}
}
。。。。。。。。。。。
}
这里我们分析Get请求,当我们进入到源码以后会发现,get方法比其他的方法复杂一点,这是因为在get 和 head 方法里面处理一个缓存,也就是这个 lastModified,这在我们前后端分离之前会用到,也就是提高get请求的性能,类似时间戳的作用。这个东西在现在的前后端分离的架构中不是很重要了。
下面我们就开始进入找到get请求的主要实现里面:
这样我们进入到一个processRequest方法,在doservice() 方法之前都是完成一些属性赋值。doservice()就是我们的核心方法
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);
//赋值一些属性 RequestAttributes 非常熟悉哈
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 {
//核心方法
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);
}
}
进入doService()核心方法:
@Override
protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
logRequest(request);
。。。。。。。。。。
//省略的代码主要是往request对象中赋值属性
try {
//核心代码
doDispatch(request, response);
}
}
三、doDispatch()核心方法
核心执行流程图:
开始分析doDispatch()核心方法,这里面完成核心流程,先来总体分析一下里面的几个核心方法,我都已经添加了注释,其实就是我们自己手写框架的时候实现的几个步骤。
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 {
//检查文件上传
processedRequest = checkMultipart(request);
multipartRequestParsed = (processedRequest != request);
// Determine handler for the current request.
//获得处理器HandlerMapping,这里返回的不在单个的HandlerMapping,而是HandlerExecutionChain 处理器+拦截器链
mappedHandler = getHandler(processedRequest);
if (mappedHandler == null) {
noHandlerFound(processedRequest, response);
return;
}
// Determine handler adapter for the current request.
//获得对应的 适配器
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;
}
}
//执行拦截器前
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
// Actually invoke the handler.
//执行具体的处理器逻辑
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
if (asyncManager.isConcurrentHandlingStarted()) {
return;
}
applyDefaultViewName(processedRequest, mv);
//执行拦截器中方法
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);
}
// 处理返回结果和视图
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) 首先我们进入到 mappedHandler = getHandler(processedRequest); 这个方法,也就是完成根据URI获得处理器映射器的流程:
//这个代码是不是非常的熟悉,和我们手写框架中的代码几乎一样
@Nullable
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
if (this.handlerMappings != null) {
for (HandlerMapping mapping : this.handlerMappings) {
//获得对应的处理器+拦截器链
HandlerExecutionChain handler = mapping.getHandler(request);
if (handler != null) {
return handler;
}
}
}
return null;
}
2、mapping.getHandler(request);具体实现逻辑在模板类AbstractHandlerMapping 实现
@Override
@Nullable
public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
//获得框架内置的处理器和拦截器链
Object handler = getHandlerInternal(request);
if (handler == null) {
handler = getDefaultHandler();
}
if (handler == null) {
return null;
}
// Bean name or resolved handler?
if (handler instanceof String) {
String handlerName = (String) handler;
handler = obtainApplicationContext().getBean(handlerName);
}
//获得完整的链 核心方法
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;
}
3、getHandlerExecutionChain(handler, request);
protected HandlerExecutionChain getHandlerExecutionChain(Object handler, HttpServletRequest request) {
//获得HandlerExecutionChain对象,HandlerExecutionChain构造器方法合并interceptors到interceptorList
HandlerExecutionChain chain = (handler instanceof HandlerExecutionChain ?
(HandlerExecutionChain) handler : new HandlerExecutionChain(handler));
String lookupPath = this.urlPathHelper.getLookupPathForRequest(request, LOOKUP_PATH);
// 将adaptedInterceptors添加到chain中,并存入到initInterceptorList中
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;
}
上面几个核心方法我们获得了处理器,下面我们需要根据 处理器获得对应的适配器。
4、getHandlerAdapter(mappedHandler.getHandler());获得适配器
protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {
if (this.handlerAdapters != null) {
for (HandlerAdapter adapter : this.handlerAdapters) {
if (adapter.supports(handler)) {
return adapter;
}
}
}
throw new ServletException("No adapter for handler [" + handler +
"]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler");
}
上面的方法我们就会非常的熟悉,获得适配器的代码和我们自己手写的框架中的代码是一样的。
5、mappedHandler.applyPreHandle(processedRequest, response);执行拦截器前方法,在执行具体的处理逻辑之前执行
boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {
//获得拦截器
HandlerInterceptor[] interceptors = getInterceptors();
if (!ObjectUtils.isEmpty(interceptors)) {
for (int i = 0; i < interceptors.length; i++) {
HandlerInterceptor interceptor = interceptors[i];
//执行拦截器前方法,
if (!interceptor.preHandle(request, response, this.handler)) {
//执行拦截器后方法,规范上有规定,拦截器后的方法必须执行一次
triggerAfterCompletion(request, response, null);
return false;
}
this.interceptorIndex = i;
}
}
return true;
}
6、mv = ha.handle(processedRequest, response, mappedHandler.getHandler()); 执行具体业务逻辑
7、处理以后逻辑
//渲染视图
applyDefaultViewName(processedRequest, mv);
//执行拦截中的方法
mappedHandler.applyPostHandle(processedRequest, response, mv);
//处理返回值逻辑
rocessDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
四、小结
本文从源码分析了springmvc的执行流程,通过这次分析,对于整个执行流程有了更深入的了解, 重要的是培养我们阅读源码的习惯。