Spring MVC适配器模式实践之HandlerAdapter源码分析【享学Spring MVC】

public interface HandlerAdapter {

	// 判断当前的这个HandlerAdapter  是否 支持给与的handler
	// 因为一般来说：每个适配器只能作用于一种处理器（你总不能把手机适配器拿去用于电脑吧）
	boolean supports(Object handler);
	
	// 核心方法：利用 Handler 处理请求，然后返回一个ModelAndView 
	// DispatcherServlet最终就是调用此方法，来返回一个ModelAndView的~
	@Nullable
	ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception;
	// 同HttpServlet 的 getLastModified方法
	// Can simply return -1 if there's no support in the handler class.
	long getLastModified(HttpServletRequest request, Object handler);

}

// 适配`org.springframework.web.servlet.mvc.Controller`这种Handler
public class SimpleControllerHandlerAdapter implements HandlerAdapter {

	@Override
	public boolean supports(Object handler) {
		return (handler instanceof Controller);
	}
	// 最终执行逻辑的还是Handler啊~~~~
	@Override
	@Nullable
	public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
			throws Exception {
		return ((Controller) handler).handleRequest(request, response);
	}
	
	// 此处注意：若处理器实现了`LastModified`接口，那就委托给它了
	// 否则返回-1  表示不要缓存~
	@Override
	public long getLastModified(HttpServletRequest request, Object handler) {
		if (handler instanceof LastModified) {
			return ((LastModified) handler).getLastModified(request);
		}
		return -1L;
	}

}

// @since 2.0
public class HttpRequestHandlerAdapter implements HandlerAdapter {

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

	@Override
	public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {\
		((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;
	}

}

public class SimpleServletHandlerAdapter implements HandlerAdapter {

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

	@Override
	@Nullable
	public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
		((Servlet) handler).service(request, response);
		return null;
	}

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

}

// @since 3.1 @RequestMapping注解是Spring2.5出现的
// 注意：它实现了Ordered接口
public abstract class AbstractHandlerMethodAdapter extends WebContentGenerator implements HandlerAdapter, Ordered {
	
	// 唯一构造函数。传的false表示：忽略掉supportedMethods这个属性
	// 默认它的值是GET、POST、HEAD（见WebContentGenerator）
	public AbstractHandlerMethodAdapter() {
		// no restriction of HTTP methods by default
		super(false);
	}

	// 只处理HandlerMethod 类型的处理器。抽象方法supportsInternal默认返回true
	// 是流出的钩子可以给你自己扩展的
	@Override
	public final boolean supports(Object handler) {
		return (handler instanceof HandlerMethod && supportsInternal((HandlerMethod) handler));
	}

	// 抽象方法交给子类handleInternal去实现
	@Override
	@Nullable
	public final ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
		return handleInternal(request, response, (HandlerMethod) handler);
	}
	...
}

DispatcherServlet：
	protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
		...
		//1、根据URL（当然不一定非得是URL）匹配到一个处理器
		mappedHandler = getHandler(processedRequest);
		if (mappedHandler == null) {
			// 若匹配不到Handler处理器，就404了
			noHandlerFound(processedRequest, response);
			return;
		}

		//2、从Chain里拿出Handler（注意是Object类型哦~ ）然后找到属于它的适配器
		HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
		...
		//3、执行作用在此Handler上的所有拦截器的Pre方法
		if (!mappedHandler.applyPreHandle(processedRequest, response)) {
			return;
		}
		//4、真正执行handle方法（也就是你自己书写的逻辑方法），得到一个ModelAndView
		mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

		//5、视图渲染
		applyDefaultViewName(processedRequest, mv);
		//6、执行拦截器的post方法（可见它是视图渲染完成了才会执行的哦~）
		mappedHandler.applyPostHandle(processedRequest, response, mv);
		...
		//7、执行拦截器的afterCompletion方法（不管抛出与否）
	}