为什么不能把这个斜线省略掉呢？

在resin 3.0.9 及以前版本下，下面几种写法都是可以的，而放到Tomcat 5.0 下则抛出这个异常：
　　严重: Parse error in application web.XML
　　Java.lang.IllegalArgumentException: Invalid <url-pattern> * in filter mapping
　　 at org.apache.commons.digester.Digester.createSAXException(Digester.java:2540)
　　 at org.apache.commons.digester.Digester.createSAXException(Digester.java:2566)
　　 at org.apache.commons.digester.Digester.endElement(Digester.java:1061)
　　 at org.apache.xerces.parsers.AbstractSAXParser.endElement(Unknown Source)
　　 at org.apache.xerces.impl.XMLDocumentFragmentScannerImpl.scanEndElement(Unknown Source)
　　 at org.apache.xerces.impl.XMLDocumentFragmentScannerImpl$FragmentContentDispatcher.dispatch(Unknown Source)
　　 at org.apache.xerces.impl.XMLDocumentFragmentScannerImpl.scanDocument(Unknown Source)
　　 at org.apache.xerces.parsers.XML11Configuration.parse(Unknown Source)
　　 at org.apache.xerces.parsers.XML11Configuration.parse(Unknown Source)
　　 at org.apache.xerces.parsers.XMLParser.parse(Unknown Source)
　　 at org.apache.xerces.parsers.AbstractSAXParser.parse(Unknown Source)
　　 at org.apache.commons.digester.Digester.parse(Digester.java:1548)
　　 at org.apache.catalina.startup.ContextConfig.applicationConfig(ContextConfig.java:263)
　　 at org.apache.catalina.startup.ContextConfig.start(ContextConfig.java:624)
　　 at org.apache.catalina.startup.ContextConfig.lifecycleEvent(ContextConfig.java:216)
　　 at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:119)
　　 at org.apache.catalina.core.StandardContext.start(StandardContext.java:4290)
　　 at org.apache.catalina.core.StandardHostDeployer.start(StandardHostDeployer.java:830)
　　 at org.apache.catalina.core.StandardHost.start(StandardHost.java:991)
　　 at org.apache.catalina.manager.ManagerServlet.start(ManagerServlet.java:1322)
　　 at org.apache.catalina.manager.HtmlManagerServlet.start(HTMLManagerServlet.java:530)
　　 at org.apache.catalina.manager.HTMLManagerServlet.doGet(HTMLManagerServlet.java:104)
　　 at javax.servlet.http.HttpServlet.service(HttpServlet.java:689)
　　 at javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
　　 at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:237)
　　 at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:157)
　　 at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:214)
　　 at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104)