HandlerAdapter接口源码解析

灰太狼 2023-02-21 09:05 206阅读 0赞

> 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][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhb21pbmd5YW5n_size_16_color_FFFFFF_t_70]

##### 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);
    			}
    		}
    	}

GitHub地址：[https://github.com/mingyang66/spring-parent/tree/master/doc/base][https_github.com_mingyang66_spring-parent_tree_master_doc_base]

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[https_github.com_mingyang66_spring-parent_tree_master_doc_base]: https://github.com/mingyang66/spring-parent/tree/master/doc/base