Heritrix定制出现java.lang.reflect.InvocationTargetException问题，怎么办？？、

在定制Extractor的过程中，不能添加自己写的Extractor，报如下错误，怎么办？？
java.lang.reflect.InvocationTargetException
at org.archive.crawler.settings.SettingsHandler.instantiateModuleTypeFromClassName(SettingsHandler.java:441)
at org.apache.jsp.modules_jsp._jspService(modules_jsp.java:578)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:137)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:210)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:295)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:241)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:358)
at org.mortbay.jetty.servlet.WebApplicationHandler$Chain.doFilter(WebApplicationHandler.java:342)
at org.archive.crawler.admin.ui.RootFilter.doFilter(RootFilter.java:67)
at org.mortbay.jetty.servlet.WebApplicationHandler$Chain.doFilter(WebApplicationHandler.java:334)
at org.mortbay.jetty.servlet.WebApplicationHandler.dispatch(WebApplicationHandler.java:286)
at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:567)
at org.mortbay.http.HttpContext.handle(HttpContext.java:1807)
at org.mortbay.jetty.servlet.WebApplicationContext.handle(WebApplicationContext.java:525)
at org.mortbay.http.HttpContext.handle(HttpContext.java:1757)
at org.mortbay.http.HttpServer.service(HttpServer.java:879)
at org.mortbay.http.HttpConnection.service(HttpConnection.java:789)
at org.mortbay.http.HttpConnection.handleNext(HttpConnection.java:960)
at org.mortbay.http.HttpConnection.handle(HttpConnection.java:806)
at org.mortbay.http.SocketListener.handleConnection(SocketListener.java:218)
at org.mortbay.util.ThreadedServer.handle(ThreadedServer.java:300)
at org.mortbay.util.ThreadPool$PoolThread.run(ThreadPool.java:511)
Caused by: java.lang.InstantiationException
at sun.reflect.InstantiationExceptionConstructorAccessorImpl.newInstance(InstantiationExceptionConstructorAccessorImpl.java:30)
at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
at org.archive.crawler.settings.SettingsHandler.instantiateModuleTypeFromClassName(SettingsHandler.java:437)
... 23 more