ApplicationFilterFactory與ApplicationFilterChain-tomcat6.x源碼閱讀

2013-11-11

ApplicationFilterFactory和ApplicationFilterChain都是跟Filter相關的類，前者根據註冊在Wrapper的Filter,通過篩選成產後者,後者是多個Filter集合的管理類。

ApplicationFilterFactory
是個單例工廠類，負責爲Servlet生成FilterChain,在createFilterChain(ServletRequest, Wrapper, Servlet)方法內部,經過URL與Filter URL過濾規則配置爲Servlet生成FilterChain,具體以下：

• 取dispatcher type，用於驗證請求
• 驗證參數正確性，如驗證request
• 建立ApplicationFilterChain對象實例,爲裝載Filter作準備
• 取Wrapper所在Context上的因此Filter定義
• 按路徑(url path)匹配規則篩選Filter，添加Filter到ApplicationChain中
• 按Servlet Name匹配規則篩選Filter，添加Filter到ApplicationChian中

/**
	 * Construct and return a FilterChain implementation that will wrap the
	 * execution of the specified servlet instance. If we should not execute a
	 * filter chain at all, return <code>null</code>.
	 * 
	 * @param request
	 *            The servlet request we are processing
	 * @param servlet
	 *            The servlet instance to be wrapped
	 */
	public ApplicationFilterChain createFilterChain(ServletRequest request,
			Wrapper wrapper, Servlet servlet) {

		// get the dispatcher type
		int dispatcher = -1;
		if (request.getAttribute(DISPATCHER_TYPE_ATTR) != null) {
			Integer dispatcherInt = (Integer) request
					.getAttribute(DISPATCHER_TYPE_ATTR);
			dispatcher = dispatcherInt.intValue();
		}
		String requestPath = null;
		Object attribute = request.getAttribute(DISPATCHER_REQUEST_PATH_ATTR);

		if (attribute != null) {
			requestPath = attribute.toString();
		}

		HttpServletRequest hreq = null;
		if (request instanceof HttpServletRequest)
			hreq = (HttpServletRequest) request;
		// If there is no servlet to execute, return null
		if (servlet == null)
			return (null);

		boolean comet = false;

		// Create and initialize a filter chain object
		ApplicationFilterChain filterChain = null;
		if (request instanceof Request) {
			Request req = (Request) request;
			comet = req.isComet();
			if (Globals.IS_SECURITY_ENABLED) {
				// Security: Do not recycle
				filterChain = new ApplicationFilterChain();
				if (comet) {
					req.setFilterChain(filterChain);
				}
			} else {
				filterChain = (ApplicationFilterChain) req.getFilterChain();
				if (filterChain == null) {
					filterChain = new ApplicationFilterChain();
					req.setFilterChain(filterChain);
				}
			}
		} else {
			// Request dispatcher in use
			filterChain = new ApplicationFilterChain();
		}

		filterChain.setServlet(servlet);

		filterChain
				.setSupport(((StandardWrapper) wrapper).getInstanceSupport());

		// Acquire the filter mappings for this Context
		StandardContext context = (StandardContext) wrapper.getParent();
		FilterMap filterMaps[] = context.findFilterMaps();

		// If there are no filter mappings, we are done
		if ((filterMaps == null) || (filterMaps.length == 0))
			return (filterChain);

		// Acquire the information we will need to match filter mappings
		String servletName = wrapper.getName();

		// Add the relevant path-mapped filters to this filter chain
		for (int i = 0; i < filterMaps.length; i++) {
			if (!matchDispatcher(filterMaps[i], dispatcher)) {
				continue;
			}
			if (!matchFiltersURL(filterMaps[i], requestPath))
				continue;
			ApplicationFilterConfig filterConfig = (ApplicationFilterConfig) context
					.findFilterConfig(filterMaps[i].getFilterName());
			if (filterConfig == null) {
				; // FIXME - log configuration problem
				continue;
			}
			boolean isCometFilter = false;
			if (comet) {
				try {
					isCometFilter = filterConfig.getFilter() instanceof CometFilter;
				} catch (Exception e) {
					// Note: The try catch is there because getFilter has a lot
					// of
					// declared exceptions. However, the filter is allocated
					// much
					// earlier
				}
				if (isCometFilter) {
					filterChain.addFilter(filterConfig);
				}
			} else {
				filterChain.addFilter(filterConfig);
			}
		}

		// Add filters that match on servlet name second
		for (int i = 0; i < filterMaps.length; i++) {
			if (!matchDispatcher(filterMaps[i], dispatcher)) {
				continue;
			}
			if (!matchFiltersServlet(filterMaps[i], servletName))
				continue;
			ApplicationFilterConfig filterConfig = (ApplicationFilterConfig) context
					.findFilterConfig(filterMaps[i].getFilterName());
			if (filterConfig == null) {
				; // FIXME - log configuration problem
				continue;
			}
			boolean isCometFilter = false;
			if (comet) {
				try {
					isCometFilter = filterConfig.getFilter() instanceof CometFilter;
				} catch (Exception e) {
					// Note: The try catch is there because getFilter has a lot
					// of
					// declared exceptions. However, the filter is allocated
					// much
					// earlier
				}
				if (isCometFilter) {
					filterChain.addFilter(filterConfig);
				}
			} else {
				filterChain.addFilter(filterConfig);
			}
		}

		// Return the completed filter chain
		return (filterChain);

	}

以上ApplicationFilterFactory完成了生產ApplicationFilterChain的任務，爲Wrapper(Servlet)從Context上面篩選Filter並添加到FilterChian中。在ApplicationFilterChain中，主要是doFilter(ServletRequest, ServletResponse)方法完成Filter過濾Serlvet且最後調用servlet的service()方法的功能。

ApplicationFilterChain 在ApplicationFilterFactory完成生產FilterChain的任務後，ApplicationFIlterChain的功能則是使用FilterChain來過濾Servlet，因爲它實現了Filterchain接口，因此具備Filterchain的功能，而且最終調用servlet.service()方法，在doFilter(ServletRequest, ServletResponse)方法中調用internalDoFilter(ServletRequest, ServletResponse)來完成，首先使用Filter過濾Servlet，最後完成service方法的調用。具體以下:

• 判斷是否已通過濾到FilterChain鏈最後一個Filter，沒有則繼續調用doFilter(ServletRequest, ServletResponse)
• 在最後一個Filter過濾完成以後，也即在遞歸方法的最內部中，調用servlet.service(request, response);執行servlet
• 在完成service方法調用後，方法遞歸出來，繼續執行每一層Filter中的邏輯定義

/**
	 * 調用doFilter方法遞歸過濾servlet，在遞歸最內部調用servlet.service()
	 * @param request
	 * @param response
	 * @throws IOException
	 * @throws ServletException
	 */
	private void internalDoFilter(ServletRequest request,
			ServletResponse response) throws IOException, ServletException {

		// Call the next filter if there is one
		//判斷是否已經執行到FilterChain鏈尾部
		if (pos < n) {
			//取當前過濾Filter配置信息
			ApplicationFilterConfig filterConfig = filters[pos++];
			Filter filter = null;
			try {
				//取Filter
				filter = filterConfig.getFilter();
				//事件通知
				support.fireInstanceEvent(InstanceEvent.BEFORE_FILTER_EVENT,
						filter, request, response);
				//安全判斷
				if (Globals.IS_SECURITY_ENABLED) {
					final ServletRequest req = request;
					final ServletResponse res = response;
					Principal principal = ((HttpServletRequest) req)
							.getUserPrincipal();

					Object[] args = new Object[] { req, res, this };
					//執行調用Filter的doFilter()方法
					SecurityUtil.doAsPrivilege("doFilter", filter, classType,
							args, principal);

					args = null;
				} else {
					//執行調用Filter的doFilter()方法
					filter.doFilter(request, response, this);
				}
				//完成Filter過濾事件通知
				support.fireInstanceEvent(InstanceEvent.AFTER_FILTER_EVENT,
						filter, request, response);
			} catch (IOException e) {
				if (filter != null)
					support.fireInstanceEvent(InstanceEvent.AFTER_FILTER_EVENT,
							filter, request, response, e);
				throw e;
			} catch (ServletException e) {
				if (filter != null)
					support.fireInstanceEvent(InstanceEvent.AFTER_FILTER_EVENT,
							filter, request, response, e);
				throw e;
			} catch (RuntimeException e) {
				if (filter != null)
					support.fireInstanceEvent(InstanceEvent.AFTER_FILTER_EVENT,
							filter, request, response, e);
				throw e;
			} catch (Throwable e) {
				if (filter != null)
					support.fireInstanceEvent(InstanceEvent.AFTER_FILTER_EVENT,
							filter, request, response, e);
				throw new ServletException(sm.getString("filterChain.filter"),
						e);
			}
			return;
		}

		// We fell off the end of the chain -- call the servlet instance
		try {
			//安全校驗
			if (Globals.STRICT_SERVLET_COMPLIANCE) {
				lastServicedRequest.set(request);
				lastServicedResponse.set(response);
			}

			//調用servlet.service()事件通知
			support.fireInstanceEvent(InstanceEvent.BEFORE_SERVICE_EVENT,
					servlet, request, response);
			if ((request instanceof HttpServletRequest)
					&& (response instanceof HttpServletResponse)) {
				//安全校驗
				if (Globals.IS_SECURITY_ENABLED) {
					final ServletRequest req = request;
					final ServletResponse res = response;
					Principal principal = ((HttpServletRequest) req)
							.getUserPrincipal();
					Object[] args = new Object[] { req, res };
					SecurityUtil.doAsPrivilege("service", servlet,
							classTypeUsedInService, args, principal);
					args = null;
				} else {
					//調用servlet.service()方法
					servlet.service((HttpServletRequest) request,
							(HttpServletResponse) response);
				}
			} else {
				//調用servlet.service()方法
				servlet.service(request, response);
			}
			//完成servlet.service()調用事件通知
			support.fireInstanceEvent(InstanceEvent.AFTER_SERVICE_EVENT,
					servlet, request, response);
		} catch (IOException e) {
			support.fireInstanceEvent(InstanceEvent.AFTER_SERVICE_EVENT,
					servlet, request, response, e);
			throw e;
		} catch (ServletException e) {
			support.fireInstanceEvent(InstanceEvent.AFTER_SERVICE_EVENT,
					servlet, request, response, e);
			throw e;
		} catch (RuntimeException e) {
			support.fireInstanceEvent(InstanceEvent.AFTER_SERVICE_EVENT,
					servlet, request, response, e);
			throw e;
		} catch (Throwable e) {
			support.fireInstanceEvent(InstanceEvent.AFTER_SERVICE_EVENT,
					servlet, request, response, e);
			throw new ServletException(sm.getString("filterChain.servlet"), e);
		} finally {
			//安全校驗
			if (Globals.STRICT_SERVLET_COMPLIANCE) {
				lastServicedRequest.set(null);
				lastServicedResponse.set(null);
			}
		}

	}

在internalDoFilter(ServletRequest, ServletResponse)方法中，能夠看到servlet是在因此FilterChain最一個Filter前置過濾完成後調用，調用完成後依次遞歸出來，逆序調用FilterChain上的Filter後置過濾servlet。在Filter中能夠添加校驗邏輯，日誌記錄等信息。到目前爲止，tomcat已經完成了使用servlet處理請求信息的功能。

FilterChain的模式是設計模式中的責任鏈模式，該模式的必需要通過全部的鏈上過濾完後纔會執行最後的操做。

還堅持