spring mvc --DispatcherServlet流程理解代码示例（转）

import java.util.List;

import java.util.Locale;

 

import javax.servlet.ServletException;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

 

import org.springframework.web.servlet.HandlerAdapter;

import org.springframework.web.servlet.HandlerExceptionResolver;

import org.springframework.web.servlet.HandlerExecutionChain;

import org.springframework.web.servlet.HandlerMapping;

import org.springframework.web.servlet.ModelAndView;

import org.springframework.web.servlet.View;

import org.springframework.web.servlet.ViewResolver;

 

public class DispatcherServletDemo {

    private List<HandlerMapping> handlerMappings = null;

    private List<HandlerAdapter> handlerAdapters = null;

    private List<HandlerExceptionResolver> handlerExceptionResolvers = null;

    private List<ViewResolver> viewResolvers = null;

 

    public void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {

        ModelAndView modelAndView = null;

        Exception dispatchException = null;

        HandlerExecutionChain handlerChain = null;

 

        try {

            // get handlerChain that consisting of "handler object" and any "handler interceptors"

            handlerChain = getHandler(request);

            if (handlerChain == null) {

                response.sendError(HttpServletResponse.SC_NOT_FOUND);

                return;

            }

            // get handlerAdapter

            HandlerAdapter handlerAdapter = getHandlerAdapter(handlerChain);

            // insert "handler interceptors" preHandle method

            // call "handler object" by handlerAdapter

            modelAndView = handlerAdapter.handle(request, response, handlerChain.getHandler());

            // insert "handler interceptors" postHandle method

        } catch (Exception ex) {

            dispatchException = ex;

        }

        if (dispatchException != null) {

            modelAndView = processHandlerException(request, response, handlerChain.getHandler(), dispatchException);

        }

        if (modelAndView != null) {

            render(modelAndView, request, response);

        }

        // insert "handler interceptors" afterCompletion method

    }

 

    private HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {

        for (HandlerMapping handlerMapping : handlerMappings) {

            HandlerExecutionChain handler = handlerMapping.getHandler(request);

            if (handler != null) {

                return handler;

            }

        }

        return null;

    }

 

    private HandlerAdapter getHandlerAdapter(HandlerExecutionChain handlerChain) throws ServletException {

        for (HandlerAdapter handlerAdapter : handlerAdapters) {

            if (handlerAdapter.supports(handlerChain)) {

                return handlerAdapter;

            }

        }

        throw new ServletException("No adapter for handler");

    }

 

    private ModelAndView processHandlerException(HttpServletRequest request, HttpServletResponse response,

            Object handler, Exception dispatchException) throws Exception {

        ModelAndView exModelAndView = null;

        for (HandlerExceptionResolver handlerExceptionResolver : handlerExceptionResolvers) {

            exModelAndView = handlerExceptionResolver.resolveException(request, response, handler, dispatchException);

            if (exModelAndView != null) {

                break;

            }

        }

        if (exModelAndView != null) {

            return exModelAndView;

        }

        throw dispatchException;

    }

 

    private void render(ModelAndView modelAndView, HttpServletRequest request, HttpServletResponse response)

            throws Exception {

        Locale locale = null; // LocaleResolver

        View view = null;

        if (modelAndView.isReference()) {

            for (ViewResolver viewResolver : this.viewResolvers) {

                View v = viewResolver.resolveViewName(modelAndView.getViewName(), locale);

                if (v != null) {

                    view = v;

                    break;

                }

            }

            if (view == null) {

                throw new ServletException("Could not resolve view with the name");

            }

        } else {

            view = modelAndView.getView();

        }

        view.render(modelAndView.getModel(), request, response);

    }

}