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Spring中HandlerAdapter接口源码解析

作者:立小研先森

这篇文章主要介绍了Spring中HandlerAdapter接口源码解析,HandlerAdapter是一个适配器接口类,适配器模式是指两个不兼容接口之间的桥梁,要想让一个接口使用另外一个接口的实现中间可以加一层适配器类,需要的朋友可以参考下

HandlerAdapter接口源码

HandlerAdapter是一个适配器接口类,适配器模式是指两个不兼容接口之间的桥梁,要想让一个接口使用另外一个接口的实现中间可以加一层适配器类;举个例子:笔记本没有网线接口,那我想连接网线接通网络如何实现呢?我可以买一个以太网转换器,网线插入转换器上,转换器插入笔记本上就实现了连接网络的功能,那这个转换器起到的就是一个适配器的作用;在接口访问控制器方法的时候是通过HandlerAdapter接口的实现类来进行的,本文以最常用的RequestMappingHandlerAdapter适配器类为主线索来讲解。

接口的源码如下:

public interface HandlerAdapter {
	/**
	 * 判定是否支持传入的handler
	 */
	boolean supports(Object handler);
	/**
	 * 使用给定的handler来处理当前request请求
	 */
	@Nullable
	ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception;
	/**
	 * 返回handler最后修改的时间
	 */
	long getLastModified(HttpServletRequest request, Object handler);
}

HandlerAdapter的实现类有多个,我们以RequestMappingHandlerAdapter适配器类为主线索,而此类又是AbstractHandlerMethodAdapter抽象类的子类;

如下是RequestMappingHandlerAdapter适配器类的关系图

在这里插入图片描述

1.HandlerAdapter接口的初始化

容器加载时DispatcherServlet中的初始化方法initStrategies方法会被调用,里面的

  /**
  * 容器中HandlerAdapter接口实现类集合
  **/
  @Nullable
	private List<HandlerAdapter> handlerAdapters;	
	/**
	 * 初始化handlerAdapters集合,如果在BeanFactory中没有HandlerAdapter,那么将使用默认
	 * 的SimpleControllerHandlerAdapter
	 */
	private void initHandlerAdapters(ApplicationContext context) {
		this.handlerAdapters = null;
		//判定是否检测所有的HandlerAdapter
		if (this.detectAllHandlerAdapters) {
			//查看容器中所有实现了HandlerAdapter的bean 
			Map<String, HandlerAdapter> matchingBeans =
					BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerAdapter.class, true, false);
			if (!matchingBeans.isEmpty()) {
				this.handlerAdapters = new ArrayList<>(matchingBeans.values());
				// We keep HandlerAdapters in sorted order.
				AnnotationAwareOrderComparator.sort(this.handlerAdapters);
			}
		}
		else {
			try {
				HandlerAdapter ha = context.getBean(HANDLER_ADAPTER_BEAN_NAME, HandlerAdapter.class);
				this.handlerAdapters = Collections.singletonList(ha);
			}
			catch (NoSuchBeanDefinitionException ex) {
				// Ignore, we'll add a default HandlerAdapter later.
			}
		}

		// Ensure we have at least some HandlerAdapters, by registering
		// default HandlerAdapters if no other adapters are found.
		if (this.handlerAdapters == null) {
			this.handlerAdapters = getDefaultStrategies(context, HandlerAdapter.class);
			if (logger.isTraceEnabled()) {
				logger.trace("No HandlerAdapters declared for servlet '" + getServletName() +
						"': using default strategies from DispatcherServlet.properties");
			}
		}
	}

上面的代码是从容器中获取HandlerAdapter接口实现类的bean集合

2.RequestMappingHandlerAdapter处理request请求

前端发送过来一个request请求首先进入DispatcherServlet的doService方法,再进入doDispatch方法,那我们看下doDispatch方法的源码:

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);
				//通过request请求获取HandlerExecutionChain处理器执行程序链
        //也即通过request获取匹配的HandlerMapping实现类,通过实现类的getHandler
        //方法获取HandlerExecutionChain处理程序执行器链类,里面包含了请求对应的HandlerMethod
        //及对应的所有拦截器
				// Determine handler for the current request.
				mappedHandler = getHandler(processedRequest);
				if (mappedHandler == null) {
					noHandlerFound(processedRequest, response);
					return;
				}
				//根据上面获取到的HandlerMethod获取匹配到的适配器类
				// 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;
				}
				//根据适配器对象调用具体的方法(如:RequestMappingHandlerAdapter)
				// 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);
				}
			}
		}
	}

跳出本文分析的正文流程,来分析下AbstractHandlerMethodAdapter适配器类;

Abstract base class for {@link HandlerAdapter} implementations that support
handlers of type {@link HandlerMethod}.

源码注解说明类抽象类的实现support方法判定是否支持HandlerMethod;

	/**
	* 判定适配器类是否支持HandlerMethod
	**/
	@Override
	public final boolean supports(Object handler) {
		return (handler instanceof HandlerMethod && supportsInternal((HandlerMethod) handler));
	}

getHandlerAdapter方法实现源码:

	/**
	 * 获取可以处理handler的HandlerAdapter适配器类
	 */
	protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {
		if (this.handlerAdapters != null) {
			for (HandlerAdapter adapter : this.handlerAdapters) {
        //判定适配器类是否支持HandlerMethod
				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");
	}

ha.handle(processedRequest, response, mappedHandler.getHandler());方法会调用AbstractHandlerMethodAdapter适配器类的handle方法:

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

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

而handleInternal方法最终会调用RequestMappingHandlerAdapter类的handlerInternal方法:

@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 {
			// 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;
	}

handleInternal方法又会调用invokeHandlerMethod方法:

	@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);
			//创建HandlerMethod的子类ServletInvocableHandlerMethod的实例对象
			ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);
			if (this.argumentResolvers != null) {
        //设置参数解析器
				invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
			}
			if (this.returnValueHandlers != null) {
        //设置返回值处理程序
				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);
			}
			//调用ServletInvocableHandlerMethod类的invokeAndHandle方法
			invocableMethod.invokeAndHandle(webRequest, mavContainer);
			if (asyncManager.isConcurrentHandlingStarted()) {
				return null;
			}

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

上面的方法会涉及到参数解析器的初始化、返回值处理程序的初始化,那这些返回值处理程序和参数解析程序如何初始化的呢?RequestMappingHandlerAdapter类实现了InitializingBean接口,该类加载后会调用afterPropertiesSet方法,会对这些处理程序进行初始化;

	@Override
	public void afterPropertiesSet() {
		// Do this first, it may add ResponseBody advice beans
		initControllerAdviceCache();
		//参数解析器初始化
		if (this.argumentResolvers == null) {
			List<HandlerMethodArgumentResolver> resolvers = getDefaultArgumentResolvers();
			this.argumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
		}
    //InitBinder的参数解析器初始化
		if (this.initBinderArgumentResolvers == null) {
			List<HandlerMethodArgumentResolver> resolvers = getDefaultInitBinderArgumentResolvers();
			this.initBinderArgumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
		}
    //返回值处理程序初始化
		if (this.returnValueHandlers == null) {
			List<HandlerMethodReturnValueHandler> handlers = getDefaultReturnValueHandlers();
			this.returnValueHandlers = new HandlerMethodReturnValueHandlerComposite().addHandlers(handlers);
		}
	}

调用ServletInvocableHandlerMethod.invokeAndHandle方法源码如下:

	public void invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer,
			Object... providedArgs) throws Exception {
		//调用控制器方法,获取返回值
		Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);
		setResponseStatus(webRequest);

		if (returnValue == null) {
			if (isRequestNotModified(webRequest) || getResponseStatus() != null || mavContainer.isRequestHandled()) {
				disableContentCachingIfNecessary(webRequest);
				mavContainer.setRequestHandled(true);
				return;
			}
		}
		else if (StringUtils.hasText(getResponseStatusReason())) {
			mavContainer.setRequestHandled(true);
			return;
		}

		mavContainer.setRequestHandled(false);
		Assert.state(this.returnValueHandlers != null, "No return value handlers");
		try {
      //将返回值交给HandlerMethodReturnValueHandlerComposite返回值代理类
      //选择合适的HandlerMethodReturnValueHandler实现类处理返回值
			this.returnValueHandlers.handleReturnValue(
					returnValue, getReturnValueType(returnValue), mavContainer, webRequest);
		}
		catch (Exception ex) {
			if (logger.isTraceEnabled()) {
				logger.trace(formatErrorForReturnValue(returnValue), ex);
			}
			throw ex;
		}
	}

调用InvocableHandlerMethod.invokeForRequest方法源码:

	/**
	* 获取request请求参数,调用控制器方法
	**/
  @Nullable
	public Object invokeForRequest(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,
			Object... providedArgs) throws Exception {
		//获取request请求方法的参数
		Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs);
		if (logger.isTraceEnabled()) {
			logger.trace("Arguments: " + Arrays.toString(args));
		}
		return doInvoke(args);
	}

调用InvocableHandlerMethod.doInvoke(Object… args)方法源码:

	/**
	* 使用给定的参数调用控制器方法
	**/
	@Nullable
	protected Object doInvoke(Object... args) throws Exception {
		ReflectionUtils.makeAccessible(getBridgedMethod());
		try {
      //调用真实最终的控制器方法,并返回执行后的结果
			return getBridgedMethod().invoke(getBean(), args);
		}
		catch (IllegalArgumentException ex) {
			assertTargetBean(getBridgedMethod(), getBean(), args);
			String text = (ex.getMessage() != null ? ex.getMessage() : "Illegal argument");
			throw new IllegalStateException(formatInvokeError(text, args), ex);
		}
		catch (InvocationTargetException ex) {
			// Unwrap for HandlerExceptionResolvers ...
			Throwable targetException = ex.getTargetException();
			if (targetException instanceof RuntimeException) {
				throw (RuntimeException) targetException;
			}
			else if (targetException instanceof Error) {
				throw (Error) targetException;
			}
			else if (targetException instanceof Exception) {
				throw (Exception) targetException;
			}
			else {
				throw new IllegalStateException(formatInvokeError("Invocation failure", args), targetException);
			}
		}
	}

到此这篇关于Spring中HandlerAdapter接口源码解析的文章就介绍到这了,更多相关HandlerAdapter接口源码内容请搜索脚本之家以前的文章或继续浏览下面的相关文章希望大家以后多多支持脚本之家!

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