Spring-MVC原理简介
前言
现在服务器开发中，非常流行restful形式的接口，最为常见的开源框架有Springmvc，下面我们来简单的剖析一下
一、简单的rest接口
一个简单的rest接口一般都包含了Mapping（映射路径），参数等
@GetMapping("/videos")
public BaseResponse> searchVideos(@RequestParam("keyword") String keyword) {
List list = searchInfoService.searchVideos(keyword);
return ListResponse.list(list);
}
二、映射建立源码分析
restful接口主要使用的几个注解如下
2.1 @RestController
它是@Controller的包装注解
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
// 可以看到RestController包含了@Controller和@ResponseBody
@Controller
@ResponseBody
public @interface RestController {
@AliasFor(annotation = Controller.class)
String value() default "";
}
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
// 看到下面这个@Component注解应该就知道@Controller注解到底是什么作用了
// 相当于把这个controller注入到容器中
@Component
public @interface Controller {
@AliasFor(annotation = Component.class)
String value() default "";
}
2.2 @RequestMapping
在RequestMappingHandlerMapping中完成注解属性的解析
protected RequestMappingInfo createRequestMappingInfo(
RequestMapping requestMapping, @Nullable RequestCondition customCondition) {
RequestMappingInfo.Builder builder = RequestMappingInfo
.paths(resolveEmbeddedValuesInPatterns(requestMapping.path()))
.methods(requestMapping.method())
.params(requestMapping.params())
.headers(requestMapping.headers())
.consumes(requestMapping.consumes())
.produces(requestMapping.produces())
.mappingName(requestMapping.name());
if (customCondition != null) {
builder.customCondition(customCondition);
}
return builder.options(this.config).build();
}
但是RequestMappingHandlerMapping继承了InitializingBean，spring容器加载之后会调用下afterPropertiesSet方法，这个方法辗转会调用到AbstractHandlerMethodMapping.assertUniqueMethodMapping方法，检验url路径是否唯一，确认唯一才会把刚才得到的Mapping存放到mappingLookup这个链式hashMap中。
private void assertUniqueMethodMapping(HandlerMethod newHandlerMethod, T mapping) {
HandlerMethod handlerMethod = this.mappingLookup.get(mapping);
if (handlerMethod != null && !handlerMethod.equals(newHandlerMethod)) {
throw new IllegalStateException(
"Ambiguous mapping. Cannot map '" + newHandlerMethod.getBean() + "' method \n" +
newHandlerMethod + "\nto " + mapping + ": There is already '" +
handlerMethod.getBean() + "' bean method\n" + handlerMethod + " mapped.");
}
}
2.3 @ResponseBody
关于这个注解我们可以在RequestResponseBodyMethodProcessor类中找到痕迹
public boolean supportsReturnType(MethodParameter returnType) {
return (AnnotatedElementUtils.hasAnnotation(returnType.getContainingClass(), ResponseBody.class) ||
returnType.hasMethodAnnotation(ResponseBody.class));
}
这个类的继承结构如下：
这个类实现了接口HandlerMethodReturnValueHandler，也就是说如果supportsReturnType返回的是true，就会调用接口中的另外一个方法实现handleReturnValue，然后顺藤摸瓜，在RequestResponseBodyMethodProcessor的父类中可以看到如下代码，实际上它是通过HttpMessageConverter完成对象的转换。所以我们可以自己实现HttpMessageConverter转换对象类型
protectedvoid writeWithMessageConverters(@Nullable T value, MethodParameter returnType, ServletServerHttpRequest inputMessage, ServletServerHttpResponse outputMessage) throws IOException, HttpMediaTypeNotAcceptableException, HttpMessageNotWritableException { // 略过部分代码 // 略过部分代码 // 略过部分代码 if (selectedMediaType != null) { selectedMediaType = selectedMediaType.removeQualityValue(); // 通过HttpMessageConverter完成对象的转换。，所以我们可以自己实现HttpMessageConverter转换对象类型 for (HttpMessageConverter converter : this.messageConverters) { GenericHttpMessageConverter genericConverter = (converter instanceof GenericHttpMessageConverter ? (GenericHttpMessageConverter) converter : null); if (genericConverter != null ? ((GenericHttpMessageConverter) converter).canWrite(targetType, valueType, selectedMediaType) : converter.canWrite(valueType, selectedMediaType)) { body = getAdvice().beforeBodyWrite(body, returnType, selectedMediaType, (Class>) converter.getClass(), inputMessage, outputMessage); if (body != null) { Object theBody = body; LogFormatUtils.traceDebug(logger, traceOn -> "Writing [" + LogFormatUtils.formatValue(theBody, traceOn) + "]"); addContentDispositionHeader(inputMessage, outputMessage); if (genericConverter != null) { genericConverter.write(body, targetType, selectedMediaType, outputMessage); } else { ((HttpMessageConverter) converter).write(body, selectedMediaType, outputMessage); } } else { if (logger.isDebugEnabled()) { logger.debug("Nothing to write: null body"); } } return; } } } if (body != null) { throw new HttpMediaTypeNotAcceptableException(this.allSupportedMediaTypes); } }
2.4 @RequestParam
在有请求进来的时候将对应的参数映射到controller方法的形参中，在类RequestParamMethodArgumentResolver中做如下处理
public void contributeMethodArgument(MethodParameter parameter, @Nullable Object value,
UriComponentsBuilder builder, Map uriVariables, ConversionService conversionService) {
Class paramType = parameter.getNestedParameterType();
if (Map.class.isAssignableFrom(paramType) || MultipartFile.class == paramType || Part.class == paramType) {
return;
}
// 获取到注解中的参数名称
RequestParam requestParam = parameter.getParameterAnnotation(RequestParam.class);
String name = (requestParam == null || StringUtils.isEmpty(requestParam.name()) ?
parameter.getParameterName() : requestParam.name());
Assert.state(name != null, "Unresolvable parameter name");
// 将参数名称和参数值，放入到queryParams这个map中，然后在后面调用方法时从queryParams里面取值
if (value == null) {
if (requestParam != null &&
(!requestParam.required() || !requestParam.defaultValue().equals(ValueConstants.DEFAULT_NONE))) {
return;
}
builder.queryParam(name);
} else if (value instanceof Collection) {
for (Object element : (Collection) value) {
element = formatUriValue(conversionService, TypeDescriptor.nested(parameter, 1), element);
builder.queryParam(name, element);
}
} else {
builder.queryParam(name, formatUriValue(conversionService, new TypeDescriptor(parameter), value));
}
}
三、请求处理流程
请求处理流程我们从DispatcherServlet开始分析，先看一下它的类结构
上图的类结构看起来有点乱，我们整理一下，是不是清晰很多DispatchServlet继承了抽象的各个Servlet中方法。
再看一下请求从DispatcherServlet开始是怎么处理到我们的Controller中的，请求结果处理的流程忘记画在流程图上，主要使用triggerAfterCompletion方法完成
用简单的文字描述一下流程：请求进来判断请求类型，执行拦截器的前置处理方法，通过代码中建立好的映射关系找到controller中的方法，执行方法，然后执行拦截器中的后置处理方法。
四、处理流程源码分析
4.1 service方法
请求进来需要先将请求对象和返回对象强转
public void service(ServletRequest req, ServletResponse res)
throws ServletException, IOException {
HttpServletRequest request;
HttpServletResponse response;
try {
// 请求进来首先强制转换类型
request = (HttpServletRequest) req;
response = (HttpServletResponse) res;
} catch (ClassCastException e) {
throw new ServletException("non-HTTP request or response");
}
service(request, response);
}
然后判断请求类型
protected void service(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
//获取请求中携带的方法类型
String method = req.getMethod();
if (method.equals(METHOD_GET)) {
// 这个方法返回的就是-1
long lastModified = getLastModified(req);
if (lastModified == -1) {
// tomcat容器不支持这个功能，直接处理get请求
doGet(req, resp);
} else {
long ifModifiedSince;
try {
ifModifiedSince = req.getDateHeader(HEADER_IFMODSINCE);
} catch (IllegalArgumentException iae) {
// Invalid date header - proceed as if none was set
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
maybeSetLastModified(resp, lastModified);
doGet(req, resp);
} else {
resp.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
}
}
//判断需要处理哪一中http的请求方法
} 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 {
// 暂无其他处理请求的方法，这里就直接输出异常提示了
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);
}
}
4.2 doGet方法
doGet方法在FrameworkServlet中重写了
protected final void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
processRequest(request, response);
}
4.3 processRequest方法
处理一下上下文，并调用doService方法去处理request和response
protected final void processRequest(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
long startTime = System.currentTimeMillis();
Throwable failureCause = null;
// 初始化上下文信息
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);
}
}
4.4 doService方法
protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
logRequest(request);
// 保存请求的原始属性快照,
Map 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));
}
}
}
// 请求属性中注入上下文、处理器、主题信息等.
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);
}
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);
}
}
}
}
4.5 doDispatch方法
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 {
// 检查是否为multipart，一般文件流也是通过multipart传递的
processedRequest = checkMultipart(request);
multipartRequestParsed = (processedRequest != request);
// 获取当前请求的处理器.
mappedHandler = getHandler(processedRequest);
if (mappedHandler == null) {
noHandlerFound(processedRequest, response);
return;
}
// 获取处理器的适配器.
HandlerAdapter ha = 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;
}
}
// interceptors的前置处理方法
// interceptors的前置处理方法
// interceptors的前置处理方法
if (!mappedHandler.applyPreHandle(processedRequest, response)) {
return;
}
// 调用适配器处理请求，这里是真正处理请求地方.
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) {
// 4.3版本以后支持在异常处理器的方法上加@ExceptionHandler处理对应异常
dispatchException = new NestedServletException("Handler dispatch failed", err);
}
//处理请求结果
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);
}
}
}
}
4.6 handler
下面主要是看Springmvc的流程怎么一步步的到了controller中的接口了
public final ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
throws Exception {
return handleInternal(request, response, (HandlerMethod) handler);
}
protected ModelAndView handleInternal(HttpServletRequest request,
HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
ModelAndView mav;
checkRequest(request);
// 如果是同步的则加锁执行.
if (this.synchronizeOnSession) {
HttpSession session = request.getSession(false);
if (session != null) {
Object mutex = WebUtils.getSessionMutex(session);
synchronized (mutex) {
mav = invokeHandlerMethod(request, response, handlerMethod);
}
} else {
// No HttpSession available -> no mutex necessary
mav = invokeHandlerMethod(request, response, handlerMethod);
}
} else {
// No synchronization on session demanded at all...
mav = invokeHandlerMethod(request, response, handlerMethod);
}
if (!response.containsHeader(HEADER_CACHE_CONTROL)) {
if (getSessionAttributesHandler(handlerMethod).hasSessionAttributes()) {
applyCacheSeconds(response, this.cacheSecondsForSessionAttributeHandlers);
} else {
prepareResponse(response);
}
}
return mav;
}
protected ModelAndView invokeHandlerMethod(HttpServletRequest request,
HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
ServletWebRequest webRequest = new ServletWebRequest(request, response);
try {
WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);
// 这个方法里面会讲到怎么找到controller中的方法的
ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);
// 一系列的处理器，处理参数啊，处理结果等
ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);
if (this.argumentResolvers != null) {
invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
}
if (this.returnValueHandlers != null) {
invocableMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);
}
invocableMethod.setDataBinderFactory(binderFactory);
invocableMethod.setParameterNameDiscoverer(this.parameterNameDiscoverer);
ModelAndViewContainer mavContainer = new ModelAndViewContainer();
mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request));
modelFactory.initModel(webRequest, mavContainer, invocableMethod);
mavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect);
AsyncWebRequest asyncWebRequest = WebAsyncUtils.createAsyncWebRequest(request, response);
asyncWebRequest.setTimeout(this.asyncRequestTimeout);
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
asyncManager.setTaskExecutor(this.taskExecutor);
asyncManager.setAsyncWebRequest(asyncWebRequest);
asyncManager.registerCallableInterceptors(this.callableInterceptors);
asyncManager.registerDeferredResultInterceptors(this.deferredResultInterceptors);
if (asyncManager.hasConcurrentResult()) {
Object result = asyncManager.getConcurrentResult();
mavContainer = (ModelAndViewContainer) asyncManager.getConcurrentResultContext()[0];
asyncManager.clearConcurrentResult();
LogFormatUtils.traceDebug(logger, traceOn -> {
String formatted = LogFormatUtils.formatValue(result, !traceOn);
return "Resume with async result [" + formatted + "]";
});
invocableMethod = invocableMethod.wrapConcurrentResult(result);
}
invocableMethod.invokeAndHandle(webRequest, mavContainer);
if (asyncManager.isConcurrentHandlingStarted()) {
return null;
}
return getModelAndView(mavContainer, modelFactory, webRequest);
} finally {
webRequest.requestCompleted();
}
}
4.7 getModelFactory
private ModelFactory getModelFactory(HandlerMethod handlerMethod, WebDataBinderFactory binderFactory) {
SessionAttributesHandler sessionAttrHandler = getSessionAttributesHandler(handlerMethod);
Class handlerType = handlerMethod.getBeanType();
Set methods = this.modelAttributeCache.get(handlerType);
if (methods == null) {
//在这里找到controller中的方法
methods = MethodIntrospector.selectMethods(handlerType, MODEL_ATTRIBUTE_METHODS);
this.modelAttributeCache.put(handlerType, methods);
}
List attrMethods = new ArrayList<>();
// Global methods first
this.modelAttributeAdviceCache.forEach((clazz, methodSet) -> {
if (clazz.isApplicableToBeanType(handlerType)) {
Object bean = clazz.resolveBean();
for (Method method : methodSet) {
attrMethods.add(createModelAttributeMethod(binderFactory, bean, method));
}
}
});
for (Method method : methods) {
Object bean = handlerMethod.getBean();
attrMethods.add(createModelAttributeMethod(binderFactory, bean, method));
}
return new ModelFactory(attrMethods, binderFactory, sessionAttrHandler);
}
4.8 triggerAfterCompletion
controller中的方法执行完毕后执行这个方法
private void triggerAfterCompletion(HttpServletRequest request, HttpServletResponse response, @Nullable Exception ex)
throws Exception {
// 获取方法的拦截器
HandlerInterceptor[] interceptors = getInterceptors();
if (!ObjectUtils.isEmpty(interceptors)) {
for (int i = this.interceptorIndex; i >= 0; i--) {
HandlerInterceptor interceptor = interceptors[i];
try {
// 执行拦截器的controller完成后处理方法
interceptor.afterCompletion(request, response, this.handler, ex);
} catch (Throwable ex2) {
logger.error("HandlerInterceptor.afterCompletion threw exception", ex2);
}
}
}
}