遇到这个问题。求解，

Question

java.lang.NullPointerException

    at com.system.dao.downloadExcel.getExcelResult(downloadExcel.java:81)

    at com.system.servlet.downloadExcelServlet.doPost(downloadExcelServlet.java:65)

    at javax.servlet.http.HttpServlet.service(HttpServlet.java:641)

    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)

    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)

    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)

    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)

    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)

    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)

    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:168)

    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)

    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)

    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)

    at org.apache.coyote.htt
p11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1002)

    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:585)

    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312)

    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)

    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)

    at java.lang.Thread.run(Thread.java:744)

Answer 1

引用来自“随风香飘飘”的评论

创建sheet和初始化嗒

Answer 2

创建sheet和初始化嗒

Answer 3

空指针异常，使用前要判断是否为空