新手提问，运行时提示NullPointerException,不晓得错在哪,请有空的进来看看.
代码如下,在执行到   stmt.executeUpdate()的时候报错

public   class   UserOperation   extends   Action{
public   ActionForward   execute(
ActionMapping   mapping,
ActionForm   form,
HttpServletRequest   request,
HttpServletResponse   response)   {
GdzczjForm   searchForm   =   (GdzczjForm)   form;

String   czry_dm=searchForm.getczry_dm();
String   sjjkxybz=searchForm.getsjjkxybz();
String   sjjkqx=searchForm.getsjjkqx();
String   pwd=searchForm.getpwd();

Connection   conn   =   null;                                               //定义连接
String   sql   =   null;                                                         //定义SQL语句
PreparedStatement   stmt=null;
try   {
conn   =   Database.getConn();                                   //得到连接





sql   =   "update   dm_czry   set   sjjkxybz=?,sjjkqx=?,sjjkpwd=?   where   czry_dm=? ";

stmt   =   conn.prepareStatement(sql);

stmt.setString(1,sjjkxybz);
stmt.setString(2,sjjkqx);
stmt.setString(3,pwd);
stmt.setString(4,czry_dm);

stmt.executeUpdate();//运行到这里就出错了
                stmt.close();
}   catch(SQLException   e)   {
e.printStackTrace();
return   mapping.findForward( "faild ");
}   finally{
if(stmt!=null)   try{stmt.close();}
              catch(SQLException   ignore){}
if(conn!=null)   try{conn.close();}
              catch(SQLException   ignore){}              
             
        }
return   mapping.findForward( "success ");
}


}

错误提示如下

Error   500--Internal   Server   Error  
java.lang.NullPointerException
at   jsp_servlet.__useroperation._jspService(__useroperation.java:190)
at   weblogic.servlet.jsp.JspBase.service(JspBase.java:33)
at   weblogic.servlet.internal.ServletStubImpl$ServletInvocationAction.run(ServletStubImpl.java:1006)
at   weblogic.servlet.internal.ServletStubImpl.invokeServlet(ServletStubImpl.java:419)
at   weblogic.servlet.internal.ServletStubImpl.invokeServlet(ServletStubImpl.java:315)
at   weblogic.servlet.internal.RequestDispatcherImpl.forward(RequestDispatcherImpl.java:322)
at   org.apache.struts.action.RequestProcessor.doForward(RequestProcessor.java:1063)
at   org.apache.struts.action.RequestProcessor.processForwardConfig(RequestProcessor.java:386)
at   org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:229)
at   org.apache.struts.action.ActionServlet.process(ActionServlet.java:1194)
at   org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:432)
at   javax.servlet.http.HttpServlet.service(HttpServlet.java:760)