Servlet中的Filter在Struts2中的执行流程

1.Servlet中filter的执行流程可以依照web.xml中的filter配置进行顺序执行。我们知道web.xml中元素执行的顺序 context-param->listener->filter->servlet。

   且无论这类元素摆放位置如何，都是遵循这个原则的。

下面看个例子

web.xml的配置：

<!-- 编码过滤器 --> <filter> <filter-name>setCharacterEncoding</filter-name> <filter-class>com.company.strutstudy.web.servletstudy.filter.EncodingFilter</filter-class> <init-param> <param-name>encoding</param-name> <param-value>utf-8</param-value> </init-param> </filter> <filter-mapping> <filter-name>setCharacterEncoding</filter-name> <url-pattern>/*</url-pattern> </filter-mapping> <!-- 一个简单的sevlet读取init参数的配置 --> <servlet> <servlet-name>helloworld</servlet-name> <servlet-class>com.company.strutstudy.web.servletstudy.servlet.HelloWorldServlet</servlet-class> <init-param> <param-name>encoding</param-name> <param-value>UTF-8</param-value> </init-param> </servlet> <servlet-mapping> <servlet-name>helloworld</servlet-name> <url-pattern>/hello</url-pattern> </servlet-mapping> <!--禁用浏览器缓存的过滤器 --> <filter> <filter-name>nocachefilter</filter-name> <filter-class>com.company.strutstudy.web.servletstudy.filter.NoCacheFilter</filter-class> </filter> <filter-mapping> <filter-name>nocachefilter</filter-name> <url-pattern>/*</url-pattern> </filter-mapping>

执行结果：

before encoding utf-8 filter！ cache do the before! doservice...UTF-8 doget... dopost... cache do the after! after encoding utf-8 filter！

ps：servlet在filter配置之前，那filter也会进行执行，且在servlet之前。
2.在struts2中配置执行filter，经过debug源码发现，一旦这个filter配置在struts2的filterDispatcher后面，在filterDispatcher中的dofilter中会自动过滤掉该filter。

web.xml的配置：

<!-- 编码过滤器 --> <filter> <filter-name>setCharacterEncoding</filter-name> <filter-class>com.company.strutstudy.web.servletstudy.filter.EncodingFilter</filter-class> <init-param> <param-name>encoding</param-name> <param-value>utf-8</param-value> </init-param> </filter> <filter-mapping> <filter-name>setCharacterEncoding</filter-name> <url-pattern>/*</url-pattern> </filter-mapping>  <!-- 加载struts2核心 --> <filter> <filter-name>StrutsFilter</filter-name> <filter-class>org.apache.struts2.dispatcher.FilterDispatcher</filter-class> <init-param> <param-name>packages</param-name> <param-value>com.company.strutstudy.web.action</param-value> </init-param> </filter> <filter-mapping> <filter-name>StrutsFilter</filter-name> <url-pattern>/*</url-pattern> </filter-mapping> <!--禁用浏览器缓存的过滤器 --> <filter> <filter-name>nocachefilter</filter-name> <filter-class>com.company.strutstudy.web.servletstudy.filter.NoCacheFilter</filter-class> </filter> <filter-mapping> <filter-name>nocachefilter</filter-name> <url-pattern>/*</url-pattern> </filter-mapping>

EncodingFilter源码：

public class EncodingFilter implements Filter { private String encoding; private Map<String, String> params = new HashMap<String, String>(); // 项目结束时就已经进行销毁 public void destroy() { System.out.println("end do the encoding filter!"); params=null; encoding=null; } public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws IOException, ServletException { //UtilTimerStack.push("EncodingFilter_doFilter:"); System.out.println("before encoding " + encoding + " filter！"); req.setCharacterEncoding(encoding); // resp.setCharacterEncoding(encoding); // resp.setContentType("text/html;charset="+encoding); chain.doFilter(req, resp); System.out.println("after encoding " + encoding + " filter！"); System.err.println("----------------------------------------"); //UtilTimerStack.pop("EncodingFilter_doFilter:"); }  // 项目启动时就已经进行读取 public void init(FilterConfig config) throws ServletException { System.out.println("begin do the encoding filter!"); encoding = config.getInitParameter("encoding"); for (Enumeration e = config.getInitParameterNames(); e .hasMoreElements();) { String name = (String) e.nextElement(); String value = config.getInitParameter(name); params.put(name, value); } } }

Struts2中的FilterDipatcher中的doFilter方法源码：

      /**      * 当执行完编码Filter后，filter链表对象filterchain会执行其后的配置的filterDispatcher，随后执行该filter的dofilter方法。      */      public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {         HttpServletRequest request = (HttpServletRequest) req;         HttpServletResponse response = (HttpServletResponse) res;         ServletContext servletContext = getServletContext();         String timerKey = "FilterDispatcher_doFilter: ";         try {             UtilTimerStack.push(timerKey);             request = prepareDispatcherAndWrapRequest(request, response);             ActionMapping mapping;             try {             //得到存储Action信息的ActionMapping对象，actionMapper被注入，如何被注入待研究                 mapping = actionMapper.getMapping(request, dispatcher.getConfigurationManager());             } catch (Exception ex) {                 LOG.error("error getting ActionMapping", ex);                 dispatcher.sendError(request, response, servletContext, HttpServletResponse.SC_INTERNAL_SERVER_ERROR, ex);                 return;             }             if (mapping == null) {//如果这个请求是action请求，那么这里得到的mapping不会是null                 // there is no action in this request, should we look for a static resource?                 String resourcePath = RequestUtils.getServletPath(request);                  if ("".equals(resourcePath) && null != request.getPathInfo()) {                     resourcePath = request.getPathInfo();                 }               //如果请求的资源以/struts开头，则当作静态资源处里                 if (serveStatic && resourcePath.startsWith("/struts")) {                     findStaticResource(resourcePath, findAndCheckResources(resourcePath), request, response);                 } else {                 //否则继续往下传，知道没有filter为止                     // this is a normal request, let it pass through                     chain.doFilter(request, response);                 }                 // The framework did its job here                 return;             }            //得到存储Action信息的ActionMapping对象             dispatcher.serviceAction(request, response, servletContext, mapping);          } finally {             try {                 ActionContextCleanUp.cleanUp(req);             } finally {                 UtilTimerStack.pop(timerKey);             }         }     } 

NoCacheFilter的源码：

public class NoCacheFilter implements Filter{  public void destroy() {  }  public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException { /*           并不是所有的浏览器都能完全支持上面的三个响应头，因此最好是同时使用上面的三个响应头。 Expires数据头：值为GMT时间值，为-1指浏览器不要缓存页面 Cache-Control响应头有两个常用值： no-cache指浏览器不要缓存当前页面； ax-age:xxx指浏览器缓存页面xxx秒。  */ HttpServletResponse hres=(HttpServletResponse) res; hres.setDateHeader("Expires",-1); hres.setHeader("Cache-Control","no-cache");  hres.setHeader("Pragma","no-cache"); System.out.println("cache do the before!"); chain.doFilter(req, res); System.out.println("cache do the after!"); } public void init(FilterConfig config) throws ServletException { } }

执行结果：

before encoding utf-8 filter！ do action!  after encoding utf-8 filter！