public static ApplicationFilterChain createFilterChain(ServletRequest request,Wrapper wrapper, Servlet servlet) {
//传入参数必须有一个servlet，这个servlet是在链的末尾被调用的. 这个servlet的查找过程是根据request的URI从web.xml配置中匹配出来的// If there is no servlet to execute, return nullif (servlet == null)return null;// Create and initialize a filter chain objectApplicationFilterChain filterChain = null;if (request instanceof Request) {//.....} else {// Request dispatcher in usefilterChain = new ApplicationFilterChain();}
// 责任链上绑定一个servletfilterChain.setServlet(servlet);filterChain.setServletSupportsAsync(wrapper.isAsyncSupported());// Acquire the filter mappings for this ContextStandardContext context = (StandardContext) wrapper.getParent();FilterMap filterMaps[] = context.findFilterMaps();// If there are no filter mappings, we are doneif ((filterMaps == null) || (filterMaps.length == 0))return (filterChain);// ...
//根据web.xml中filter的配置查找是否和当前request匹配// Add the relevant path-mapped filters to this filter chainfor (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 problemcontinue;}// 和request URI匹配，则filter会加入到责任链中filterChain.addFilter(filterConfig);}/.....// Return the completed filter chainreturn filterChain;}

 1 private void internalDoFilter(ServletRequest request,
 2                                   ServletResponse response)
 3         throws IOException, ServletException {
 4
 5         // Call the next filter if there is one
 6         if (pos < n) {
 7             //调用下一个filter, 每调用一次 当前pos都会++
 8             ApplicationFilterConfig filterConfig = filters[pos++];
 9             try {
10                 Filter filter = filterConfig.getFilter();
11
12                 //...
13                     filter.doFilter(request, response, this);
14
15             } catch (IOException | ServletException | RuntimeException e) {
16                 throw e;
17             } catch (Throwable e) {
18                // ...
19             }
20             return;
21         }
22
23         // We fell off the end of the chain -- call the servlet instance
24         try {
25             if (request.isAsyncSupported() && !servletSupportsAsync) {
26                 request.setAttribute(Globals.ASYNC_SUPPORTED_ATTR,
27                         Boolean.FALSE);
28             }
29             // ...  在链的末尾，调用具体servlet的doService
30                 servlet.service(request, response);
31             //
32         } catch (IOException | ServletException | RuntimeException e) {
33             throw e;
34         } catch (Throwable e) {
35            //...
36         } finally {
37            //...
38         }
39     }