以前项目用的是tomcat7，然后由于客户那边是tomcat6，现在又换回6版本。但是在项目启动的时候，报以下错误：
2014-3-31 10:22:38 org.apache.catalina.core.StandardWrapperValve invoke 严重: Servlet.service() for servlet jsp threw exception java.lang.ClassNotFoundException: org.apache.tomcat.InstanceManager at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1680) at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1526) at org.apache.jasper.servlet.JasperLoader.loadClass(JasperLoader.java:128) at org.apache.jasper.servlet.JasperLoader.loadClass(JasperLoader.java:66) at java.lang.ClassLoader.loadClassInternal(Unknown Source) at java.lang.Class.getDeclaredFields0(Native Method) at java.lang.Class.privateGetDeclaredFields(Unknown Source) at java.lang.Class.getDeclaredFields(Unknown Source) at org.apache.catalina.util.DefaultAnnotationProcessor.processAnnotations(DefaultAnnotationProcessor.java:181) at org.apache.jasper.servlet.JspServletWrapper.getServlet(JspServletWrapper.java:153) at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:340) at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313) at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260) at javax.servlet.http.HttpServlet.service(HttpServlet.java:723) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.springframework.orm.hibernate3.support.OpenSessionInViewFilter.doFilterInternal(OpenSessionInViewFilter.java:198) at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88) at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:76) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293) at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:861) at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:606) at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489) at java.lang.Thread.run(Unknown Source) 2014-3-31 10:22:38 org.apache.catalina.core.ApplicationDispatcher invoke 严重: Servlet.service() for servlet jsp threw exception java.lang.ClassNotFoundException: org.apache.tomcat.InstanceManager at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1680) at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1526) at org.apache.jasper.servlet.JasperLoader.loadClass(JasperLoader.java:128) at org.apache.jasper.servlet.JasperLoader.loadClass(JasperLoader.java:66) at java.lang.ClassLoader.loadClassInternal(Unknown Source) at java.lang.Class.getDeclaredFields0(Native Method) at java.lang.Class.privateGetDeclaredFields(Unknown Source) at java.lang.Class.getDeclaredFields(Unknown Source) at org.apache.catalina.util.DefaultAnnotationProcessor.processAnnotations(DefaultAnnotationProcessor.java:181) at org.apache.jasper.servlet.JspServletWrapper.getServlet(JspServletWrapper.java:153) at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:340) at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313) at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260) at javax.servlet.http.HttpServlet.service(HttpServlet.java:723) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:646) at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:438) at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:374) at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:302) at org.apache.catalina.core.StandardHostValve.custom(StandardHostValve.java:421) at org.apache.catalina.core.StandardHostValve.throwable(StandardHostValve.java:270) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:141) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293) at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:861) at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:606) at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489) at java.lang.Thread.run(Unknown Source) 2014-3-31 10:22:38 org.apache.catalina.core.StandardHostValve custom 严重: Exception Processing ErrorPage[exceptionType=java.lang.Exception, location=/comm/error.jsp] javax.servlet.ServletException: java.lang.NoClassDefFoundError: Lorg/apache/tomcat/InstanceManager; at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:268) at javax.servlet.http.HttpServlet.service(HttpServlet.java:723) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:646) at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:438) at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:374) at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:302) at org.apache.catalina.core.StandardHostValve.custom(StandardHostValve.java:421) at org.apache.catalina.core.StandardHostValve.throwable(StandardHostValve.java:270) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:141) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293) at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:861) at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:606) at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489) at java.lang.Thread.run(Unknown Source) Caused by: java.lang.NoClassDefFoundError: Lorg/apache/tomcat/InstanceManager; at java.lang.Class.getDeclaredFields0(Native Method) at java.lang.Class.privateGetDeclaredFields(Unknown Source) at java.lang.Class.getDeclaredFields(Unknown Source) at org.apache.catalina.util.DefaultAnnotationProcessor.processAnnotations(DefaultAnnotationProcessor.java:181) at org.apache.jasper.servlet.JspServletWrapper.getServlet(JspServletWrapper.java:153) at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:340) at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313) at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260) ... 17 more Caused by: java.lang.ClassNotFoundException: org.apache.tomcat.InstanceManager at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1680) at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1526) at org.apache.jasper.servlet.JasperLoader.loadClass(JasperLoader.java:128) at org.apache.jasper.servlet.JasperLoader.loadClass(JasperLoader.java:66) at java.lang.ClassLoader.loadClassInternal(Unknown Source) ... 25 more
后来解决了，貌似是因为tomcat6 访问tomcat7编译好的项目并不会重新编译，所以此时访问会造成一些jar包找不到的错误。
解决方案：Project-clean（tomcat6对项目进行重新编译）