java - java.lang.NullPointerException 更新时发生？

Question

我得到空指针异常 "java.lang.NullPointerException" 参考下面的代码供参考一切都应该没问题但无法将数据更新到数据库（mySql）

<% try{
        //reading request parameters

          String projectName=request.getParameter("projectName").trim();
          String status=request.getParameter("status").trim();

          //String user = session.getAttribute("user").toString();
          Connection connection = DAO.getConnection();
          PreparedStatement pstmt = connection.prepareStatement("update project set status=? where projectName=?");

          pstmt.setString(1,status);
          pstmt.executeUpdate();                    
          out.println("<h2 style='color:green'>Project Status has been updated</h2>");
    }
    catch(Exception ex)
    {
          ex.printStackTrace();
          out.println("<h2 style='color:red'>Please login to update your Status</h2>");
    }
%>

由于异常无法更新请参阅下面请任何人建议我如何解决此异常...

java.lang.NullPointerException 在 org.apache.jsp.MyWorkPanelAction_jsp._jspService(MyWorkPanelAction_jsp.java:93) 在 org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70) 在 javax.servlet.http.HttpServlet。服务（HttpServlet.java:728）在 org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432) 在 org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390) 在 org.apache .jasper.servlet.JspServlet.service(JspServlet.java:334) at javax.servlet.http.HttpServlet.service(HttpServlet.java:728) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305 ) 在 org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210) 在 org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222) org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123) org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502) org.apache.catalina.core .StandardHostValve.invoke(StandardHostValve.java:171) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99) at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408) at org.apache.coyote.http11.AbstractHttp11Processor.process( AbstractHttp11Processor.java:1023) 在 org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589) 在 org.apache。tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310) at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at java .lang.Thread.run（未知来源）

标签： javanullpointerexception

Answer 1

您错过了项目名称...试试下面的代码

try{
        //reading request parameters

          String projectName=request.getParameter("projectName").trim();
          String status=request.getParameter("status").trim();

          //String user = session.getAttribute("user").toString();
          Connection connection = DAO.getConnection();
          PreparedStatement pstmt = connection.prepareStatement("update project set status=? where projectName=?");

          pstmt.setString(1,status);
          pstmt.setString(2,projectName); //Try this

          pstmt.executeUpdate();                    
          out.println("<h2 style='color:green'>Project Status has been updated</h2>");
    }
    catch(Exception ex)
    {
          ex.printStackTrace();
          out.println("<h2 style='color:red'>Please login to update your Status</h2>");
    }