java.lang.NullPointerException pstmt = conn.prepareStatement(sql)報錯

時間 2019-12-06

標籤 java.lang.nullpointerexception java lang nullpointerexception pstmt conn.preparestatement conn preparestatement sql 報錯欄目 Java 简体版

原文原文鏈接

        報錯狀況以下：java.lang.NullPointerException
   at com.test.servlet.BookQueryServlet.doPost(BookQueryServlet.java:73)
   at javax.servlet.http.HttpServlet.service(HttpServlet.java:646)
   at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
   at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
   at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
   at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
   at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
   at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
   at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
   at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
   at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:504)
   at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)
   at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
   at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950)
   at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
   at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:421)
   at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1074)
   at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:611)
   at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:316)
   at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
   at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
   at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)

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

解決措施：不一樣於通常Java項目，JavaWeb項目須要把相關驅動放在WebRoot下面的WEB-INF/lib下面web

而不能經過右鍵->Build Path-> Add External JARs
apache