前言
上篇文章中分析了各個容器相關的 Pipeline 屬性對象的 的 Valve 屬性對象的 invoke 方法。在最後的 StandardWrapperValve 方法裏調用 ApplicationFilterChain#doFilter 方法,本文分析一下這個方法。java
1. ApplicationFilterChain#doFiltersegmentfault
/** * Invoke the next filter in this chain, passing the specified request * and response. If there are no more filters in this chain, invoke * the <code>service()</code> method of the servlet itself. * * @param request The servlet request we are processing * @param response The servlet response we are creating * * @exception IOException if an input/output error occurs * @exception ServletException if a servlet exception occurs */ @Override public void doFilter(ServletRequest request, ServletResponse response) throws IOException, ServletException { if( Globals.IS_SECURITY_ENABLED ) { final ServletRequest req = request; final ServletResponse res = response; try { java.security.AccessController.doPrivileged( new java.security.PrivilegedExceptionAction<Void>() { @Override public Void run() throws ServletException, IOException { internalDoFilter(req,res); return null; } } ); } catch( PrivilegedActionException pe) { Exception e = pe.getException(); if (e instanceof ServletException) throw (ServletException) e; else if (e instanceof IOException) throw (IOException) e; else if (e instanceof RuntimeException) throw (RuntimeException) e; else throw new ServletException(e.getMessage(), e); } } else { internalDoFilter(request,response); } }
doFilter 方法就是簡單調用 internalDoFilter 方法。
2. ApplicationFilterChain#internalDoFilter數組
/** * The int which is used to maintain the current position * in the filter chain. */ private int pos = 0; /** * The int which gives the current number of filters in the chain. */ private int n = 0; private void internalDoFilter(ServletRequest request, ServletResponse response) throws IOException, ServletException { // Call the next filter if there is one if (pos < n) { ApplicationFilterConfig filterConfig = filters[pos++]; try { Filter filter = filterConfig.getFilter(); if (request.isAsyncSupported() && "false".equalsIgnoreCase( filterConfig.getFilterDef().getAsyncSupported())) { request.setAttribute(Globals.ASYNC_SUPPORTED_ATTR, Boolean.FALSE); } 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}; SecurityUtil.doAsPrivilege ("doFilter", filter, classType, args, principal); } else { filter.doFilter(request, response, this); } } catch (IOException | ServletException | RuntimeException e) { throw e; } catch (Throwable e) { e = ExceptionUtils.unwrapInvocationTargetException(e); ExceptionUtils.handleThrowable(e); throw new ServletException(sm.getString("filterChain.filter"), e); } return; } // We fell off the end of the chain -- call the servlet instance try { if (ApplicationDispatcher.WRAP_SAME_OBJECT) { lastServicedRequest.set(request); lastServicedResponse.set(response); } if (request.isAsyncSupported() && !servletSupportsAsync) { request.setAttribute(Globals.ASYNC_SUPPORTED_ATTR, Boolean.FALSE); } // Use potentially wrapped request from this point if ((request instanceof HttpServletRequest) && (response instanceof HttpServletResponse) && 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); } else { servlet.service(request, response); } } catch (IOException | ServletException | RuntimeException e) { throw e; } catch (Throwable e) { e = ExceptionUtils.unwrapInvocationTargetException(e); ExceptionUtils.handleThrowable(e); throw new ServletException(sm.getString("filterChain.servlet"), e); } finally { if (ApplicationDispatcher.WRAP_SAME_OBJECT) { lastServicedRequest.set(null); lastServicedResponse.set(null); } } }
internalDoFilter 方法裏分了兩部分,if (pos < n) 和 if 後面的 try-catch 語句。tomcat
先從 filter 是數組裏獲取下一個 ApplicationFilterConfig 對象。app
ApplicationFilterConfig filterConfig = filters[pos++];
而後經過 filterConfig.getFilter() 獲取一個 Filter 對象,並調用這個 Filter 的 doFilter 方法,並把 ApplicationFilterChain 對象傳入 Filter#doFilteride
在 if (pos < n) 裏的 n 是這個 ApplicationFilterChain 裏包含的 Filter 的總數。this
每次調用 internalDoFilter 方法,pos 就加1,也就是獲取下一個 ApplicationFilterConfig,直到 pos 等於 n 的時候纔不執行 if 語句,爲了達到這個效果,應用程序必須在自定義的在 Filter 裏執行 FilterChain#doFilter 方法,才能再次進入 ApplicationFilterChain#internalDoFilter 方法,這樣就完成了調用 ApplicationFilterChain 裏全部的 Filter 的 doFilter 方法。
這種方式是責任鏈模式的一種體現。spa
internalDoFilter裏的 try-catch 是在執行完全部的 Filter#doFilter 方法以後執行的。
try 語句塊裏先設置一下屬性,而後執行code
servlet.service(request, response);
經過調用 Servlet 對象的 service 方法來處理請求。對象
到這裏,tomcat 終於把請求交給了應用程序了,tomcat 整個接受請求、轉發處理請求的流程就差很少完結了。
小結本文分析了 ApplicationFilterChain#doFilter 方法,在這個方法裏,tomcat 首先調用了 ApplicationFilterChain 裏全部 Filter 的 doFilter 方法,而後調用 ApplicationFilterChain 裏的 Servlet 對象的 service 方法把請求交給了應用程序。