Tomcat8.x Servlet内部跳转机制 req.getRequestDispatcher("...").forward(req, resp);

// Servlet内部跳转的源代码片段 req.getRequestDispatcher("...").forward(req, resp);
// req.getRequestDispatcher("/hello?parmam1=value1¶m2=value2").forward(req, resp);

// Servlet内部跳转的源代码片段 req.getRequestDispatcher("...").forward(req, resp);
		// req.getRequestDispatcher("/hello?parmam1=value1¶m2=value2").forward(req, resp);
		
		// 取得转发器  ----------------------- 1
		// req.getRequestDispatcher("/hello?parmam1=value1¶m2=value2") ==== org.apache.catalina.core.ApplicationDispatcher
		class org.apache.catalina.connector.RequestFacade{
			public RequestDispatcher getRequestDispatcher(String path) {
				return request.getRequestDispatcher(path);//!!!
			}
		}
		
		class org.apache.catalina.connector.Request{
			public RequestDispatcher getRequestDispatcher(String path) {
				Context context = getContext(); // org.apache.catalina.core.StandardContext
				if (path == null) {
		            return null;
		        } else if (path.startsWith("/")) {
		        	// !!! org.apache.catalina.core.ApplicationContextFacade.getRequestDispatcher("/a/hello-servlet")
		            return (context.getServletContext().getRequestDispatcher(path));
		        }
			}
		}
		
		class org.apache.catalina.core.ApplicationContextFacade{
			public RequestDispatcher getRequestDispatcher(final String path) {
	        	// context == org.apache.catalina.core.ApplicationContext
	            return context.getRequestDispatcher(path);
		    }
		}

		class org.apache.catalina.core.ApplicationContext{
			public RequestDispatcher getRequestDispatcher(String path) {
	
		    	// path == "/hello?parmam1=value1¶m2=value2"
		    	
		    	// path = "/a/b/c/file.jsp"
		    	// path = "/a/b/c/HelloServlet"
		        // Get query string
		        String queryString = null;
		        String normalizedPath = path;
		        int pos = normalizedPath.indexOf('?');
		        if (pos >= 0) {
		            queryString = normalizedPath.substring(pos + 1); // 有带参数  "parmam1=value1¶m2=value2"
		            normalizedPath = normalizedPath.substring(0, pos); // 标准的地址  "/hello"
		        }
	
		        pos = normalizedPath.length();
	
		        // Use the thread local URI and mapping data
		        DispatchData dd = dispatchData.get();
		        if (dd == null) { // 每个线程有各自的副本!!!
		            dd = new DispatchData();
		            dispatchData.set(dd);
		        }
	
		        MessageBytes uriMB = dd.uriMB;
		        uriMB.recycle();
	
		        // Use the thread local mapping data
		        MappingData mappingData = dd.mappingData;
	
		        // Map the URI
		        CharChunk uriCC = uriMB.getCharChunk();
		        try {
		        	// org.apache.catalina.core.StandardContext
		        	// 如:/example
		            uriCC.append(context.getPath(), 0, context.getPath().length());
		            /*
		             * Ignore any trailing path params (separated by ';') for mapping
		             * purposes
		             */
		            int semicolon = normalizedPath.indexOf(';');
		            if (pos >= 0 && semicolon > pos) {
		                semicolon = -1;
		            }
		            uriCC.append(normalizedPath, 0, semicolon > 0 ? semicolon : pos);
		            // uriMB === "/example/a/b/c/file.jsp"
		            // uriMB === "/example/a/b/c/file.jsp"
		            // uriMB === "/example/a/b/c/HellorvSelet"
		            // uriMB === "/test/hello"
		            service.getMapper().map(context, uriMB, mappingData);//!!!! 匹配路由
		            if (mappingData.wrapper == null) { // 找到包装器
		                return (null);
		            }
		            /*
		             * Append any trailing path params (separated by ';') that were
		             * ignored for mapping purposes, so that they're reflected in the
		             * RequestDispatcher's requestURI
		             */
		            if (semicolon > 0) {
		                uriCC.append(normalizedPath, semicolon, pos - semicolon);
		            }
		        } catch (Exception e) {
		            // Should never happen
		            log(sm.getString("applicationContext.mapping.error"), e);
		            return (null);
		        }
		        
	//	      
	//				    HelloServlet
	//				    /hello/*
	//			
		        // 转发地址:/hello?parmam1=value1¶m2=value2
		        // org.apache.catalina.core.StandardWrapper
		        Wrapper wrapper = mappingData.wrapper; // 匹配的StandardWrapper
		        String wrapperPath = mappingData.wrapperPath.toString(); // 如:"/hello"
		        String pathInfo = mappingData.pathInfo.toString();// null
		        Mapping mapping = (new ApplicationMapping(mappingData)).getMapping(); // 创建映射对象,来保存匹配到的信息
	
		        mappingData.recycle(); // 回收掉原来映射器的信息
	
		        String encodedUri = URLEncoder.DEFAULT.encode(uriCC.toString()); // 如: "/test/hello"
	
		        // Construct a RequestDispatcher to process this request
		        // org.apache.catalina.core.ApplicationDispatcher
		        return new ApplicationDispatcher(wrapper, encodedUri, wrapperPath, pathInfo,
		                queryString, mapping, null);
		    }
		}
		
		
		// 调用转发器的forward方法  ----------------------- 2
		// ApplicationDispatcher.forward(req, resp);
		class org.apache.catalina.core.ApplicationDispatcher{
			// 构造函数
			public ApplicationDispatcher(Wrapper wrapper, String requestURI, String servletPath,
		         String pathInfo, String queryString, Mapping mapping, String name) {
	
		        super();
		        // Save all of our configuration parameters
		        this.wrapper = wrapper; // org.apache.catalina.core.StandardWrapper
		        this.context = (Context) wrapper.getParent();
		        this.requestURI = requestURI;
		        this.servletPath = servletPath;
		        this.pathInfo = pathInfo;
		        this.queryString = queryString;
		        this.mapping = mapping;
		        this.name = name;
		    }
			
			// 内部跳转
			public void forward(ServletRequest request, ServletResponse response)
			        throws ServletException, IOException
		    {
	            doForward(request,response);//!!!! 跳转
		    }
			
			private void doForward(ServletRequest request, ServletResponse response)
			        throws ServletException, IOException
		    {
				// 清除数据,回收空间
	            // 不回收编码转换器
	        	// org.apache.catalina.connector.ResponseFacade
	            response.resetBuffer(); 
	            State state = new State(request, response, false); // 创建state对象
	            wrapResponse(state);//!!! 包裹org.apache.catalina.connector.ResponseFacade对象
	         // 包裹 request == org.apache.catalina.connector.RequestFacade
	            ApplicationHttpRequest wrequest =
	                (ApplicationHttpRequest) wrapRequest(state);
	            String contextPath = context.getPath(); // 如: “/test”
	            HttpServletRequest hrequest = state.hrequest; 
	            // hrequest == org.apache.catalina.connector.RequestFacade
	            // wrequest == org.apache.catalina.connector.ApplicationHttpRequest
	            if (hrequest.getAttribute(RequestDispatcher.FORWARD_REQUEST_URI) == null) {
	            	// 把原请求对象RequestFacade的信息,放入新的请求对象ApplicationHttpRequest
	                wrequest.setAttribute(RequestDispatcher.FORWARD_REQUEST_URI,
	                                      hrequest.getRequestURI());
	                wrequest.setAttribute(RequestDispatcher.FORWARD_CONTEXT_PATH,
	                                      hrequest.getContextPath());
	                wrequest.setAttribute(RequestDispatcher.FORWARD_SERVLET_PATH,
	                                      hrequest.getServletPath());
	                wrequest.setAttribute(RequestDispatcher.FORWARD_PATH_INFO,
	                                      hrequest.getPathInfo());
	                wrequest.setAttribute(RequestDispatcher.FORWARD_QUERY_STRING,
	                                      hrequest.getQueryString());
	                Mapping mapping;
	                if (hrequest instanceof org.apache.catalina.servlet4preview.http.HttpServletRequest) {
	                    mapping = ((org.apache.catalina.servlet4preview.http.HttpServletRequest)
	                            hrequest).getMapping(); // 取得路由匹配信息
	                } else {
	                    mapping = (new ApplicationMapping(null)).getMapping();
	                }
	                wrequest.setAttribute(
	                        org.apache.catalina.servlet4preview.RequestDispatcher.FORWARD_MAPPING,
	                        mapping);
	            }

	            // 设置新的请求对象ApplicationHttpRequest的信息
	            wrequest.setContextPath(contextPath);
	            wrequest.setRequestURI(requestURI);
	            wrequest.setServletPath(servletPath);
	            wrequest.setPathInfo(pathInfo);
	            if (queryString != null) {
	                wrequest.setQueryString(queryString);
	                wrequest.setQueryParams(queryString);
	            }
	            wrequest.setMapping(mapping);

	            //  request == org.apache.catalina.connector.RequestFacade
	            //  response == org.apache.catalina.connector.ResponseFacade
	            processRequest(request,response,state); // 处理请求
	            
	            ((ResponseFacade) response).finish(); // 结束请求
	            
	            PrintWriter writer = response.getWriter(); // 关闭输出对象
                writer.close();
		    }
			
			// 处理请求
			private void processRequest(ServletRequest request,
                    ServletResponse response,
                    State state)
				throws IOException, ServletException {
				
				//  request == org.apache.catalina.connector.RequestFacade
				//  response == org.apache.catalina.connector.ResponseFacade
				
				// context === org.apache.catalina.core.StandardContext
	            if (context.getFireRequestListenersOnForwards() &&
	                    !context.fireRequestInitEvent(request)) { // 如果有配置监听器,就出发跳转监听器
	                doInvoke = false;
	            }
	            // state.outerRequest ==  org.apache.catalina.connector.RequestFacade
                // response == org.apache.catalina.connector.ResponseFacade
                invoke(state.outerRequest, response, state);
			}
			
			// 调用
			private void invoke(ServletRequest request, ServletResponse response,
		            State state) throws IOException, ServletException {
		    	
		    	// request ==  org.apache.catalina.connector.RequestFacade
		        // response == org.apache.catalina.connector.ResponseFacade
			
				// wrapper == org.apache.catalina.core.StandardWrapper 是Servlet的包装器
            	// !!!!! 加载Servlet类,创建Servlet对象,反射Servlet对象内部的注解,如:@Resource声明的资源,并进行依赖注入到Servlet对象中!!!
                // !!!!! 调用Servlet对象的init方法
                servlet = wrapper.allocate();

                // Get the FilterChain Here  创建过滤器链条
                ApplicationFilterChain filterChain =
                        ApplicationFilterFactory.createFilterChain(request, wrapper, servlet);
                if ((servlet != null) && (filterChain != null)) {
                    filterChain.doFilter(request, response); // 执行过滤链条
                }
                filterChain.release();  // 回收过滤器链条的资源
                wrapper.deallocate(servlet); // 回收Servlet的资源
			}
		}




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