java中使用jxl导出excel文件

[快乐的走在路上]

在执行：
finally {
if (os != null) {
os.close();
}
if (wwb != null) {
wwb.close();
}
} 中wwb.close();语句时报错，求教大神。
java.lang.NullPointerException
at jxl.write.biff.File.close(File.java:116)
at jxl.write.biff.WritableWorkbookImpl.close(WritableWorkbookImpl.java:447)
at com.app.jbxx.action.cxtj.CbtjAction.cbtjDc_xjjyyy(CbtjAction.java:249)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at com.zpf.base.action.BizDispatchAction.dispatchMethod(BizDispatchAction.java:199)
at com.zpf.base.action.BizDispatchAction.execute(BizDispatchAction.java:105)
at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:419)
at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:224)
at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1194)
at org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:432)
at com.zpf.webcontroller.MainServlet.doPost(MainServlet.java:161)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
at com.zpf.webcontroller.MainServlet.service(MainServlet.java:147)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at com.zpf.webcontroller.MainServlet.service(MainServlet.java:131)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:269)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188)
at com.zpf.webcontroller.safe.SaftyFilter.doFilter(SaftyFilter.java:153)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:215)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188)
at com.zpf.webcontroller.EncodingFilter.doFilter(EncodingFilter.java:44)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:215)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:172)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:117)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:108)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:174)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:875)
at org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:665)
at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:528)
at org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:81)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:689)
at java.lang.Thread.run(Thread.java:619)

[三仙半]

你在关闭os时是不是已经把wwb给关闭了？例如，连接数据库时，关闭连接，那么，依赖这个连接的statement和RecordSet就会同时被关闭。 你可以先关闭wwb，然后再关闭os试试，如果不报错，那么我刚才的猜测就是正确的。

[快乐的走在路上]

试了下，还是报错哦。

[快乐的走在路上]

引用 1 楼 zys59 的回复:

你在关闭os时是不是已经把wwb给关闭了？例如，连接数据库时，关闭连接，那么，依赖这个连接的statement和RecordSet就会同时被关闭。 你可以先关闭wwb，然后再关闭os试试，如果不报错，那么我刚才的猜测就是正确的。

试了下，还是报这样的错。

[三仙半]

出错的是你的文件的哪一行，是wwb的问题还是os的问题？Debug一下，看看，出错的那个变量到底被赋值没有，或者赋值了以后什么时候又变成null了

[qq_36030659]

空指针异常，debug看看是不是哪个为空呢。java实现导出excel文件，简单点其实可以用PageOffice插件实现的。