Spring-DispatcherServlet请求处理

Spring-DispatcherServlet初始化详解：http://donald-draper.iteye.com/blog/2325394
Spring的DefaultAnnotationHandlerMapping详解：http://donald-draper.iteye.com/blog/2325453
前面我们已经探究过DispatcherServlet的初始化，下面我们来看看
DispatcherServlet如何处理web请求
//DispatcherServlet

 public class DispatcherServlet extends FrameworkServlet
{
}

从DispatcherServlet我们看不到任何请求处理入口再来看FrameworkServlet

public abstract class FrameworkServlet extends HttpServletBean
    implements ApplicationContextAware
{
 public FrameworkServlet(WebApplicationContext webApplicationContext)
    {
        contextClass = DEFAULT_CONTEXT_CLASS;
        contextInitializers = new ArrayList();
        publishContext = true;
        publishEvents = true;
        threadContextInheritable = false;
        dispatchOptionsRequest = false;
        dispatchTraceRequest = false;
        webApplicationContextInjected = false;
        refreshEventReceived = false;
        this.webApplicationContext = webApplicationContext;
    }
    //在这里我们发现了处理请求的方法，默认方法
     protected void service(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException
    {
        String method = request.getMethod();
        if(method.equalsIgnoreCase(RequestMethod.PATCH.name()))
            processRequest(request, response);
        else
            super.service(request, response);
    }
    //GET
    protected final void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException
    {
        processRequest(request, response);
    }
    //POST
    protected final void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException
    {
        processRequest(request, response);
    }
    //PUT
    protected final void doPut(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException
    {
        processRequest(request, response);
    }
    //DELETE
    protected final void doDelete(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException
    {
        processRequest(request, response);
    }
    //实际处理请求方法
    protected final void processRequest(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException
    {
        try
        {
	   //处理请求
            doService(request, response);
        }
    }
    //带子类DispatcherServlet扩展
     protected abstract void doService(HttpServletRequest httpservletrequest, HttpServletResponse httpservletresponse)
        throws Exception;
    public static final String DEFAULT_NAMESPACE_SUFFIX = "-servlet";
    public static final Class DEFAULT_CONTEXT_CLASS = org/springframework/web/context/support/XmlWebApplicationContext;
    public static final String SERVLET_CONTEXT_PREFIX = (new StringBuilder()).append(org/springframework/web/servlet/FrameworkServlet.getName()).append(".CONTEXT.").toString();
    private static final String INIT_PARAM_DELIMITERS = ",; \t\n";
    private String contextAttribute;
    private Class contextClass;
    private String contextId;
    private String namespace;
    private String contextConfigLocation;
    private final ArrayList contextInitializers;
    private String contextInitializerClasses;
    private boolean publishContext;
    private boolean publishEvents;
    private boolean threadContextInheritable;
    private boolean dispatchOptionsRequest;
    private boolean dispatchTraceRequest;
    private WebApplicationContext webApplicationContext;
    private boolean webApplicationContextInjected;
    private boolean refreshEventReceived;
}

我们来看DispatcherServlet

public class DispatcherServlet extends FrameworkServlet
{
 public DispatcherServlet(WebApplicationContext webApplicationContext)
    {
        super(webApplicationContext);
        detectAllHandlerMappings = true;
        detectAllHandlerAdapters = true;
        detectAllHandlerExceptionResolvers = true;
        detectAllViewResolvers = true;
        throwExceptionIfNoHandlerFound = false;
        cleanupAfterInclude = true;
    }
    //处理请求
     protected void doService(HttpServletRequest request, HttpServletResponse response)
        throws Exception
    {
        //设置请求属性，web上下文，本地化，主题
        request.setAttribute(WEB_APPLICATION_CONTEXT_ATTRIBUTE, getWebApplicationContext());
        request.setAttribute(LOCALE_RESOLVER_ATTRIBUTE, localeResolver);
        request.setAttribute(THEME_RESOLVER_ATTRIBUTE, themeResolver);
        request.setAttribute(THEME_SOURCE_ATTRIBUTE, getThemeSource());
        FlashMap inputFlashMap = flashMapManager.retrieveAndUpdate(request, response);
        if(inputFlashMap != null)
            request.setAttribute(INPUT_FLASH_MAP_ATTRIBUTE, Collections.unmodifiableMap(inputFlashMap));
        request.setAttribute(OUTPUT_FLASH_MAP_ATTRIBUTE, new FlashMap());
        request.setAttribute(FLASH_MAP_MANAGER_ATTRIBUTE, flashMapManager);
	//委托给doDispatch
        doDispatch(request, response);
        
    }

    protected void doDispatch(HttpServletRequest request, HttpServletResponse response)
        throws Exception
    {
        HttpServletRequest processedRequest;
        HandlerExecutionChain mappedHandler;
        boolean multipartRequestParsed;
        WebAsyncManager asyncManager;
        processedRequest = request;
        mappedHandler = null;
        multipartRequestParsed = false;
        asyncManager = WebAsyncUtils.getAsyncManager(request);
        ModelAndView mv;
        Exception dispatchException;
        mv = null;
        dispatchException = null;
        processedRequest = checkMultipart(request);
        multipartRequestParsed = processedRequest != request;
	//获取控制器处理器链
        mappedHandler = getHandler(processedRequest);
        HandlerAdapter ha;
        //获取控制器方法适配器
        ha = getHandlerAdapter(mappedHandler.getHandler());
	//获取处理视图
        mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
	//返回视图
        applyDefaultViewName(request, mv);
    }
   //获取控制器处理器链
   protected HandlerExecutionChain getHandler(HttpServletRequest request)
        throws Exception
    {   
       //List<HashMap<String,HandlerMapping>>
        for(Iterator iterator = handlerMappings.iterator(); iterator.hasNext();)
        { 
            HandlerMapping hm = (HandlerMapping)iterator.next();
            if(logger.isTraceEnabled())
                logger.trace((new StringBuilder()).append("Testing handler map [").append(hm).append("] in DispatcherServlet with name '").append(getServletName()).append("'").toString());
            HandlerExecutionChain handler = hm.getHandler(request);
            if(handler != null)
                return handler;
        }
    }
    //获取控制器方法适配器
    protected HandlerAdapter getHandlerAdapter(Object handler)
        throws ServletException
    {
        //List<HashMap<String,HandlerAdapter>>
        for(Iterator iterator = handlerAdapters.iterator(); iterator.hasNext();)
        {
            HandlerAdapter ha = (HandlerAdapter)iterator.next();
            if(logger.isTraceEnabled())
                logger.trace((new StringBuilder()).append("Testing handler adapter [").append(ha).append("]").toString());
            if(ha.supports(handler))
                return ha;
        }
    }
    private List handlerMappings;//List<HashMap<String,HandlerMapping>>,Key为beanName，value值为HandlerMapping实例
    private List handlerAdapters;//List<HashMap<String,HandlerAdapter>>,Key为beanName，value值为HandlerAdapter实例
    private List handlerExceptionResolvers;
    private List viewResolvers;

    static 
    {
        try
        {
	    //加载默认配置文件
            ClassPathResource resource = new ClassPathResource("DispatcherServlet.properties", org/springframework/web/servlet/DispatcherServlet);
            defaultStrategies = PropertiesLoaderUtils.loadProperties(resource);
        }
    }
}

总结：
DispatcherServlet处理请求实际上是通过FrameworkServlet的Service()和do*类方法，
而这些方式实际的处理逻辑在DispatcherServlet的doService和doDispatch中，doDispatch
先找出控制器处理器，然后再找出控制器方法适配器，通过控制器方法适配器，来处理具体请求。