SpringMVC(十一)-----HandlerAdapter

目錄

• 推薦公衆号
• 引言
• 上一篇
• 正文
• • 類關系
  • 簡介

推薦公衆号

有彩蛋哦!!!(或者公衆号内點選網賺擷取彩蛋)

引言

之前介紹了，來了一個請求之後，DispatcherServlet如何找打需要執行的方法，現在介紹DispatcherServlet如何執行方法

上一篇

SpringMVC(十)-----AbstractHandlerMethodMapping根據request找HandlerMethod

https://blog.csdn.net/yueloveme/article/details/89917049

正文

類關系

簡介

HttpRequestHandlerAdapter 執行HttpRequestHandler的handleRequest方法

SimpleServletHandlerAdapter 執行的是HttpServlet的service方法

RequestMappingHandlerAdapter執行@RequestMapping注解的方法

SimpleControllerHandlerAdapter 執行Controller的handleRequest方法

public interface HandlerAdapter {

	/**
	 * 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
	 */
	 判斷 是否支援 傳入的 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
	 */
	 執行Handler處理請求
	@Nullable
	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
	 */
	 擷取目前請求的最後更改時間，主要用于供給浏覽器判斷目前請求是否修改過，進而判
	 斷是否可以直接使用之前緩存的結果
	long getLastModified(HttpServletRequest request, Object handler);

}
           

在DispatcherServlet中的位置

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
// Determine handler adapter for the current request.
擷取 執行HandlerMethod的HandlerAdapter
				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 (logger.isDebugEnabled()) {
						logger.debug("Last-Modified value for [" + 
						getRequestUri(request) + "] is: " + lastModified);
					}
					if (new ServletWebRequest(request, 
					response).checkNotModified(lastModified) && isGet) {
						return;
					}
				}

				if (!mappedHandler.applyPreHandle(processedRequest, 
				response)) {
					return;
				}
				執行
				// Actually invoke the handler.
				mv = ha.handle(processedRequest, response, 
				mappedHandler.getHandler());

/**
	 * Return the HandlerAdapter for this handler object.
	 * @param handler the handler object to find an adapter for
	 * @throws ServletException if no HandlerAdapter can be found for the handler. This is a fatal error.
	 */
	 擷取 執行HandlerMethod的HandlerAdapter
	protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {
		if (this.handlerAdapters != null) {
			for (HandlerAdapter ha : this.handlerAdapters) {
				if (logger.isTraceEnabled()) {
					logger.trace("Testing handler adapter [" + ha + "]");
				}
				if (ha.supports(handler)) {
					return ha;
				}
			}
		}
		throw new ServletException("No adapter for handler [" + handler +
				"]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler");
	}