SpringMVC源码情操陶冶-HandlerAdapter适配器简析

springmvc中对业务的具体处理是通过HandlerAdapter适配器操作的

HandlerAdapter接口方法

列表如下

/**
	 * Given a handler instance, return whether or not this {@code HandlerAdapter}
	 * can support it. Typical HandlerAdapters will base the decision on the handler
	 * type. HandlerAdapters will usually only support one handler type each.
	 * <p>A typical implementation:
	 * <p>{@code
	 * return (handler instanceof MyHandler);
	 * }
	 * @param handler handler object to check
	 * @return whether or not this object can use the given handler
	 */
	boolean supports(Object handler);

	/**
	 * Use the given handler to handle this request.
	 * The workflow that is required may vary widely.
	 * @param request current HTTP request
	 * @param response current HTTP response
	 * @param handler handler to use. This object must have previously been passed
	 * to the {@code supports} method of this interface, which must have
	 * returned {@code true}.
	 * @throws Exception in case of errors
	 * @return ModelAndView object with the name of the view and the required
	 * model data, or {@code null} if the request has been handled directly
	 */
	ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception;

	/**
	 * Same contract as for HttpServlet's {@code getLastModified} method.
	 * Can simply return -1 if there's no support in the handler class.
	 * @param request current HTTP request
	 * @param handler handler to use
	 * @return the lastModified value for the given handler
	 * @see javax.servlet.http.HttpServlet#getLastModified
	 * @see org.springframework.web.servlet.mvc.LastModified#getLastModified
	 */
	long getLastModified(HttpServletRequest request, Object handler);

下面针对以上接口对springmvc内置的实现类作下简析

AbstractHandlerMethodAdapter-处理HandlerMethod业务

处理handler类型为HandlerMethod.class的请求，这是常用的请求方式，一般都是返回视图给前台页面

	@Override
	public final boolean supports(Object handler) {
		return (handler instanceof HandlerMethod && supportsInternal((HandlerMethod) handler));
	
	@Override
	public final ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
			throws Exception {
		//供子类实现调用
		return handleInternal(request, response, (HandlerMethod) handler);
	}

	@Override
	public final long getLastModified(HttpServletRequest request, Object handler) {
		//供子类实现调用
		return getLastModifiedInternal(request, (HandlerMethod) handler);
	}

以下看下主要实现类RequestMappingHandlerAdapter的具体实现代码

RequestMappingHandlerAdapter#supportsInternal()

直接返回true，表明handler为HandlerMethod对象即可

	@Override
	protected boolean supportsInternal(HandlerMethod handlerMethod) {
		return true;
	}

RequestMappingHandlerAdapter#handleInternal()-业务处理逻辑

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

		ModelAndView mav;
		//确定请求是否符合,比如是否为GET/POST请求，可配置
		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 {
			//最终通过invokeHandlerMethod()方法创建ModelAndView视图对象，这里涉及到反射机制使用
			mav = invokeHandlerMethod(request, response, handlerMethod);
		}
		//设置关于cache的头部信息
		if (!response.containsHeader(HEADER_CACHE_CONTROL)) {
			if (getSessionAttributesHandler(handlerMethod).hasSessionAttributes()) {
				applyCacheSeconds(response, this.cacheSecondsForSessionAttributeHandlers);
			}
			else {
				prepareResponse(response);
			}
		}

		return mav;
	}

RequestMappingHandlerAdapter的关键方法invokeHandlerMethod()，采用的是反射的思想来获取视图对象，有兴趣的可自行查阅分析

HttpRequestHandlerAdapter-处理HttpRequestHandler接口业务

处理handler类型为HttpRequestHandler.class的请求，简单的http请求，常用的有静态资源映射请求ResourceHttpRequestHandler，其包装在SimpleUrlHandlerMapping中，具体可看>>>SpringMVC源码情操陶冶-ResourcesBeanDefinitionParser静态资源解析器

	@Override
	public boolean supports(Object handler) {
		return (handler instanceof HttpRequestHandler);
	}

	@Override
	public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
			throws Exception {
		//调用handleRequest()接口方法直接返回内容给前端
		//ResourceHttpRequestHandler返回请求的静态资源文件给前端
		((HttpRequestHandler) handler).handleRequest(request, response);
		return null;
	}

	@Override
	public long getLastModified(HttpServletRequest request, Object handler) {
		if (handler instanceof LastModified) {
			return ((LastModified) handler).getLastModified(request);
		}
		return -1L;
	}

SimpleControllerHandlerAdapter-处理Controller接口业务

处理handler类型为Controller.class的请求，一般不采用

@Override
	public boolean supports(Object handler) {
		return (handler instanceof Controller);
	}

	@Override
	public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
			throws Exception {
		//调用Controller接口类的接口方法handleRequest()方法直接响应给前端
		return ((Controller) handler).handleRequest(request, response);
	}

	@Override
	public long getLastModified(HttpServletRequest request, Object handler) {
		if (handler instanceof LastModified) {
			return ((LastModified) handler).getLastModified(request);
		}
		return -1L;
	}

SimpleServletHandlerAdapter-处理Servlet接口业务

处理handler类型为Servlet.class的请求，一般不采用

	@Override
	public boolean supports(Object handler) {
		return (handler instanceof Servlet);
	}

	@Override
	public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
			throws Exception {
		//直接调用Servlet的service接口返回
		((Servlet) handler).service(request, response);
		return null;
	}

	@Override
	public long getLastModified(HttpServletRequest request, Object handler) {
		return -1;
	}