springboot 请求响应处理流程

发表于 2023-08-27 更新于 2023-09-05 分类于 Java ， SpringBoot 阅读次数：阅读次数： Disqus：

Tomcat 会把请求委托到
org.springframework.web.servlet.DispatcherServlet#doService

protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
		logRequest(request);

        // 省略前面的代码
		try {
			doDispatch(request, response);
		}

然后就是调用
org.springframework.web.servlet.DispatcherServlet#doDispatch

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {

	try {
		ModelAndView mv = null;
		Exception dispatchException = null;

		try {
			processedRequest = checkMultipart(request);
			multipartRequestParsed = (processedRequest != request);

               // 去获取处理器
			// 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 = HttpMethod.GET.matches(method);
			if (isGet || HttpMethod.HEAD.matches(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());

看下这里的逻辑

@Nullable
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
	if (this.handlerMappings != null) {
		for (HandlerMapping mapping : this.handlerMappings) {
			HandlerExecutionChain handler = mapping.getHandler(request);
			if (handler != null) {
				return handler;
			}
		}
	}
	return null;
}

可以看到有这些 HandlerMapping

而这里面就是前面提到过的
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping
从这就能找到具体的 Handler
com.nicksxs.spbdemo.controller.DemoController#test()
这就是我简单的示例代码

@RequestMapping(value = "/test", method = RequestMethod.GET)
@ResponseBody
public DemoResponse test() {
    String item = "{\"id\": 1, \"name\": \"nick\"}";
    ParserConfig parserConfig = ParserConfig.getGlobalInstance();
    parserConfig.propertyNamingStrategy = PropertyNamingStrategy.SnakeCase;
    DemoResponse response = JSON.parseObject(item, DemoResponse.class, parserConfig);
    return response;
}

下一步是再获取处理器的适配器，
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter

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");
	}

正好这个适配器是调用的父类的 supports 方法

@Override
public final boolean supports(Object handler) {
	return (handler instanceof HandlerMethod && supportsInternal((HandlerMethod) handler));
}

而我这个com.nicksxs.spbdemo.controller.DemoController#test()
就是个包装好的 HandlerMethod
然后就是调用 ha 的 handle 方法，也是通过模板方法，实际调用的是
org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter#handle

@Override
@Nullable
public final ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
		throws Exception {

	return handleInternal(request, response, (HandlerMethod) handler);
}

然后调用
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter#handleInternal

@Override
	protected ModelAndView handleInternal(HttpServletRequest request,
			HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {

		ModelAndView mav;
		checkRequest(request);

		// Execute invokeHandlerMethod in synchronized block if required.
		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 {
            // 是否要锁定 session，否则走到这
			// No synchronization on session demanded at all...
			mav = invokeHandlerMethod(request, response, handlerMethod);
		}

继续调用
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter#invokeHandlerMethod

@Nullable
	protected ModelAndView invokeHandlerMethod(HttpServletRequest request,
			HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {

		ServletWebRequest webRequest = new ServletWebRequest(request, response);
		try {
			WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);
			ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);

            // 包装调用方法，
			ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);
			// 省略一部分非本次关注核心代码
            // 然后是调用到这
			invocableMethod.invokeAndHandle(webRequest, mavContainer);
			if (asyncManager.isConcurrentHandlingStarted()) {
				return null;
			}

			return getModelAndView(mavContainer, modelFactory, webRequest);
		}
		finally {
			webRequest.requestCompleted();
		}
	}

稍微再看一眼
第一步是
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter#createInvocableHandlerMethod

protected ServletInvocableHandlerMethod createInvocableHandlerMethod(HandlerMethod handlerMethod) {
	return new ServletInvocableHandlerMethod(handlerMethod);
}

第二步是
org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod#ServletInvocableHandlerMethod(org.springframework.web.method.HandlerMethod)

   public ServletInvocableHandlerMethod(HandlerMethod handlerMethod) {
	super(handlerMethod);
}

第三步是
org.springframework.web.method.support.InvocableHandlerMethod#InvocableHandlerMethod(org.springframework.web.method.HandlerMethod)

   public InvocableHandlerMethod(HandlerMethod handlerMethod) {
	super(handlerMethod);
}

第四步是
org.springframework.web.method.HandlerMethod#HandlerMethod(org.springframework.web.method.HandlerMethod)

protected HandlerMethod(HandlerMethod handlerMethod) {
	Assert.notNull(handlerMethod, "HandlerMethod is required");
	this.bean = handlerMethod.bean;
	this.beanFactory = handlerMethod.beanFactory;
	this.beanType = handlerMethod.beanType;
	this.method = handlerMethod.method;
	this.bridgedMethod = handlerMethod.bridgedMethod;
	this.parameters = handlerMethod.parameters;
	this.responseStatus = handlerMethod.responseStatus;
	this.responseStatusReason = handlerMethod.responseStatusReason;
	this.description = handlerMethod.description;
	this.resolvedFromHandlerMethod = handlerMethod.resolvedFromHandlerMethod;
}

这是个继承关系，一直调用到最顶层的父类的构造方法，其实就是拷贝，然后继续调用
org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod#invokeAndHandle

public void invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer,
			Object... providedArgs) throws Exception {

        // 调用请求
		Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);
		// 稍微忽略下后面的代码
	}

继续调用
org.springframework.web.method.support.InvocableHandlerMethod#invokeForRequest

@Nullable
public Object invokeForRequest(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,
		Object... providedArgs) throws Exception {

	Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs);
	if (logger.isTraceEnabled()) {
		logger.trace("Arguments: " + Arrays.toString(args));
	}
	return doInvoke(args);
}

来到了最核心处
org.springframework.web.method.support.InvocableHandlerMethod#doInvoke

@Nullable
protected Object doInvoke(Object... args) throws Exception {
	Method method = getBridgedMethod();
	ReflectionUtils.makeAccessible(method);
	try {
		if (KotlinDetector.isSuspendingFunction(method)) {
			return CoroutinesUtils.invokeSuspendingFunction(method, getBean(), args);
		}
           // 会走到这里，获取到 bean，而这个 bean 就是前面构造方法里赋值的，最开始被放在 handler 里面，然后调用方法
		return method.invoke(getBean(), args);
	}