websphere 中SystemOut.log显示报错信息：抛出的异常：javax.servlet.ServletException

websphere 中SystemOut.log显示报错信息：

[11-10-8 16:08:11:529 CST] 00000020 ServletWrappe E   SRVE0068E: 未捕获到 servlet FilterProxyServlet 的其中一个服务方法中抛出的异常。抛出的异常：javax.servlet.ServletException
 at com.ibm.ws.webcontainer.filter.WebAppFilterChain.doFilter(WebAppFilterChain.java:166)
 at com.ibm.ws.webcontainer.filter.WebAppFilterChain._doFilter(WebAppFilterChain.java:87)
 at com.ibm.ws.webcontainer.filter.WebAppFilterManager.doFilter(WebAppFilterManager.java:761)
 at com.ibm.ws.webcontainer.filter.WebAppFilterManager.doFilter(WebAppFilterManager.java:673)
 at com.ibm.ws.webcontainer.servlet.ServletWrapper.handleRequest(ServletWrapper.java:498)
 at com.ibm.ws.wswebcontainer.servlet.ServletWrapper.handleRequest(ServletWrapper.java:464)
 at com.ibm.wsspi.webcontainer.servlet.GenericServletWrapper.handleRequest(GenericServletWrapper.java:122)
 at com.ibm.ws.jsp.webcontainerext.AbstractJSPExtensionServletWrapper.handleRequest(AbstractJSPExtensionServletWrapper.java:196)
 at com.ibm.ws.webcontainer.webapp.WebAppRequestDispatcher.forward(WebAppRequestDispatcher.java:308)
 at com.ibm.ws.webcontainer.servlet.FilterProxyServlet.dispatch(FilterProxyServlet.java:73)
 at com.ibm.ws.webcontainer.servlet.FilterProxyServlet.service(FilterProxyServlet.java:52)
 at com.ibm.ws.webcontainer.servlet.ServletWrapper.service(ServletWrapper.java:989)
 at com.ibm.ws.webcontainer.servlet.ServletWrapper.service(ServletWrapper.java:930)
 at com.ibm.ws.webcontainer.filter.WebAppFilterChain.doFilter(WebAppFilterChain.java:145)
 at com.topsoft.writ.web.javabean.SetEncodingFilter.doFilter(SetEncodingFilter.java:42)
 at com.ibm.ws.webcontainer.filter.FilterInstanceWrapper.doFilter(FilterInstanceWrapper.java:190)
 at com.ibm.ws.webcontainer.filter.WebAppFilterChain.doFilter(WebAppFilterChain.java:130)
 at com.ibm.ws.webcontainer.filter.WebAppFilterChain._doFilter(WebAppFilterChain.java:87)
 at com.ibm.ws.webcontainer.filter.WebAppFilterManager.doFilter(WebAppFilterManager.java:761)
 at com.ibm.ws.webcontainer.filter.WebAppFilterManager.doFilter(WebAppFilterManager.java:673)
 at com.ibm.ws.webcontainer.filter.WebAppFilterManager.invokeFilters(WebAppFilterManager.java:688)
 at com.ibm.ws.wswebcontainer.filter.WebAppFilterManager.invokeFilters(WebAppFilterManager.java:96)
 at com.ibm.ws.webcontainer.extension.DefaultExtensionProcessor.invokeFilters(DefaultExtensionProcessor.java:652)
 at com.ibm.ws.webcontainer.extension.DefaultExtensionProcessor.handleRequest(DefaultExtensionProcessor.java:472)
 at com.ibm.ws.wswebcontainer.extension.DefaultExtensionProcessor.handleRequest(DefaultExtensionProcessor.java:113)
 at com.ibm.ws.webcontainer.webapp.WebApp.handleRequest(WebApp.java:3168)
 at com.ibm.ws.webcontainer.webapp.WebGroup.handleRequest(WebGroup.java:254)
 at com.ibm.ws.webcontainer.WebContainer.handleRequest(WebContainer.java:811)
 at com.ibm.ws.wswebcontainer.WebContainer.handleRequest(WebContainer.java:1433)
 at com.ibm.ws.webcontainer.channel.WCChannelLink.ready(WCChannelLink.java:96)
 at com.ibm.ws.http.channel.inbound.impl.HttpInboundLink.handleDiscrimination(HttpInboundLink.java:465)
 at com.ibm.ws.http.channel.inbound.impl.HttpInboundLink.handleNewInformation(HttpInboundLink.java:394)
 at com.ibm.ws.http.channel.inbound.impl.HttpInboundLink.ready(HttpInboundLink.java:274)
 at com.ibm.ws.tcp.channel.impl.NewConnectionInitialReadCallback.sendToDiscriminators(NewConnectionInitialReadCallback.java:214)
 at com.ibm.ws.tcp.channel.impl.NewConnectionInitialReadCallback.complete(NewConnectionInitialReadCallback.java:113)
 at com.ibm.ws.tcp.channel.impl.AioReadCompletionListener.futureCompleted(AioReadCompletionListener.java:152)
 at com.ibm.io.async.AbstractAsyncFuture.invokeCallback(AbstractAsyncFuture.java:213)
 at com.ibm.io.async.AbstractAsyncFuture.fireCompletionActions(AbstractAsyncFuture.java:195)
 at com.ibm.io.async.AsyncFuture.completed(AsyncFuture.java:136)
 at com.ibm.io.async.ResultHandler.complete(ResultHandler.java:194)
 at com.ibm.io.async.ResultHandler.runEventProcessingLoop(ResultHandler.java:741)
 at com.ibm.io.async.ResultHandler$2.run(ResultHandler.java:863)
 at com.ibm.ws.util.ThreadPool$Worker.run(ThreadPool.java:1469)
---- Begin backtrace for Nested Throwables
java.lang.NullPointerException
 at com.ibm._jsp._login._jspService(_login.java:86)
 at com.ibm.ws.jsp.runtime.HttpJspBase.service(HttpJspBase.java:85)
 at javax.servlet.http.HttpServlet.service(HttpServlet.java:856)
 at com.ibm.ws.webcontainer.servlet.ServletWrapper.service(ServletWrapper.java:989)
 at com.ibm.ws.webcontainer.servlet.ServletWrapper.service(ServletWrapper.java:930)
 at com.ibm.ws.webcontainer.filter.WebAppFilterChain.doFilter(WebAppFilterChain.java:118)
 at com.ibm.ws.webcontainer.filter.WebAppFilterChain._doFilter(WebAppFilterChain.java:87)
 at com.ibm.ws.webcontainer.filter.WebAppFilterManager.doFilter(WebAppFilterManager.java:761)
 at com.ibm.ws.webcontainer.filter.WebAppFilterManager.doFilter(WebAppFilterManager.java:673)
 at com.ibm.ws.webcontainer.servlet.ServletWrapper.handleRequest(ServletWrapper.java:498)
 at com.ibm.ws.wswebcontainer.servlet.ServletWrapper.handleRequest(ServletWrapper.java:464)
 at com.ibm.wsspi.webcontainer.servlet.GenericServletWrapper.handleRequest(GenericServletWrapper.java:122)
 at com.ibm.ws.jsp.webcontainerext.AbstractJSPExtensionServletWrapper.handleRequest(AbstractJSPExtensionServletWrapper.java:196)
 at com.ibm.ws.webcontainer.webapp.WebAppRequestDispatcher.forward(WebAppRequestDispatcher.java:308)
 at com.ibm.ws.webcontainer.servlet.FilterProxyServlet.dispatch(FilterProxyServlet.java:73)
 at com.ibm.ws.webcontainer.servlet.FilterProxyServlet.service(FilterProxyServlet.java:52)
 at com.ibm.ws.webcontainer.servlet.ServletWrapper.service(ServletWrapper.java:989)
 at com.ibm.ws.webcontainer.servlet.ServletWrapper.service(ServletWrapper.java:930)
 at com.ibm.ws.webcontainer.filter.WebAppFilterChain.doFilter(WebAppFilterChain.java:145)
 at com.topsoft.writ.web.javabean.SetEncodingFilter.doFilter(SetEncodingFilter.java:42)
 at com.ibm.ws.webcontainer.filter.FilterInstanceWrapper.doFilter(FilterInstanceWrapper.java:190)
 at com.ibm.ws.webcontainer.filter.WebAppFilterChain.doFilter(WebAppFilterChain.java:130)
 at com.ibm.ws.webcontainer.filter.WebAppFilterChain._doFilter(WebAppFilterChain.java:87)
 at com.ibm.ws.webcontainer.filter.WebAppFilterManager.doFilter(WebAppFilterManager.java:761)
 at com.ibm.ws.webcontainer.filter.WebAppFilterManager.doFilter(WebAppFilterManager.java:673)
 at com.ibm.ws.webcontainer.filter.WebAppFilterManager.invokeFilters(WebAppFilterManager.java:688)
 at com.ibm.ws.wswebcontainer.filter.WebAppFilterManager.invokeFilters(WebAppFilterManager.java:96)
 at com.ibm.ws.webcontainer.extension.DefaultExtensionProcessor.invokeFilters(DefaultExtensionProcessor.java:652)
 at com.ibm.ws.webcontainer.extension.DefaultExtensionProcessor.handleRequest(DefaultExtensionProcessor.java:472)
 at com.ibm.ws.wswebcontainer.extension.DefaultExtensionProcessor.handleRequest(DefaultExtensionProcessor.java:113)
 at com.ibm.ws.webcontainer.webapp.WebApp.handleRequest(WebApp.java:3168)
 at com.ibm.ws.webcontainer.webapp.WebGroup.handleRequest(WebGroup.java:254)
 at com.ibm.ws.webcontainer.WebContainer.handleRequest(WebContainer.java:811)
 at com.ibm.ws.wswebcontainer.WebContainer.handleRequest(WebContainer.java:1433)
 at com.ibm.ws.webcontainer.channel.WCChannelLink.ready(WCChannelLink.java:96)
 at com.ibm.ws.http.channel.inbound.impl.HttpInboundLink.handleDiscrimination(HttpInboundLink.java:465)
 at com.ibm.ws.http.channel.inbound.impl.HttpInboundLink.handleNewInformation(HttpInboundLink.java:394)
 at com.ibm.ws.http.channel.inbound.impl.HttpInboundLink.ready(HttpInboundLink.java:274)
 at com.ibm.ws.tcp.channel.impl.NewConnectionInitialReadCallback.sendToDiscriminators(NewConnectionInitialReadCallback.java:214)
 at com.ibm.ws.tcp.channel.impl.NewConnectionInitialReadCallback.complete(NewConnectionInitialReadCallback.java:113)
 at com.ibm.ws.tcp.channel.impl.AioReadCompletionListener.futureCompleted(AioReadCompletionListener.java:152)
 at com.ibm.io.async.AbstractAsyncFuture.invokeCallback(AbstractAsyncFuture.java:213)
 at com.ibm.io.async.AbstractAsyncFuture.fireCompletionActions(AbstractAsyncFuture.java:195)
 at com.ibm.io.async.AsyncFuture.completed(AsyncFuture.java:136)
 at com.ibm.io.async.ResultHandler.complete(ResultHandler.java:194)
 at com.ibm.io.async.ResultHandler.runEventProcessingLoop(ResultHandler.java:741)
 at com.ibm.io.async.ResultHandler$2.run(ResultHandler.java:863)
 at com.ibm.ws.util.ThreadPool$Worker.run(ThreadPool.java:1469)

请问这个是怎么回事？怎么解决？