Question

我得到了空指针异常 "java.lang.NullPointerException" 请参考以下代码以供参考一切都应该很好，但不能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>");
    }
%>

由于异常而无法更新参考下面请任何人建议我如何解决此异常...

org.apache.jsp.MyWorkPanelAction_jsp._jspService（MyWorkPanelAction_jsp.java:93）上的
java.lang.NullPointerException 在org.apache.jasper.runtime.HttpJspBase.service（HttpJspBase.java:70）在javax.servlet.http.HttpServlet.service（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）在javax.servlet.http.HttpServlet.service（HttpServlet.java:728）在 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）在 org.apache.catalina.core.StandardContextValve.invoke（StandardContextValve.java:123）在 org.apache.catalina.authenticator.AuthenticatorBase.invoke（AuthenticatorBase.java:502）在 org.apache.catalina.core.StandardHostValve.invoke（StandardHostValve.java:171）在 org.apache.catalina.valves.ErrorReportValve.invoke（ErrorReportValve.java:99）在 org.apache.catalina.valves.AccessLogValve.invoke（AccessLogValve.java:953）在 org.apache.catalina.core.StandardEngineValve.invoke（StandardEngineValve.java:118）在 org.apache.catalina.connector.CoyoteAdapter.service（CoyoteAdapter.java:408）在 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）在java.util.concurrent.ThreadPoolExecutor.runWorker（未知来源）在java.util.concurrent.ThreadPoolExecutor $ Worker.run（未知来源）在java.lang.Thread.run（未知来源）

Answer 1

您错过了projectName ...请尝试下面的代码

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>");
    }

我更新时会发生java.lang.NullPointerException吗？

1 个答案: