tomcat ported to Google App Engine

Question

I had the period webservice originally tomcat server. Now I want to segment webservice transplant to GAE. I transplant was successful. Implementation, but this error message is displayed. Will this cause the possibility of error?

MY CODE:

 public class LOAD extends HttpServlet{
        static String JBx;
        static String JBy;
        static String JBSx;
        static String JBSy;
        static String gps;
        String a;
        int i;
          private Connection con = null; //Database objects 
          private Statement stat = null; 
          private ResultSet rs = null; 
          private PreparedStatement pst = null; 
        private String dropdbSQL = "DROP TABLE User "; 

      private String createdbSQL = "CREATE TABLE User (" + 
        "    id     INTEGER " + 
        "  , name    VARCHAR(20) " + 
        "  , passwd  VARCHAR(20))"; 

      private String insertdbSQL = "insert into User(id,gps,recopy) " + 
              "select ifNULL(max(id),0)+1,?,? FROM User"; 

      private String selectSQL = "select * from User "; 
      public static void main(String[] args) 
      { 


      } 
          public void SelectTable() 
          { 
            try 
            { 
              stat = con.createStatement(); 
              rs = stat.executeQuery(selectSQL); 
              while(rs.next()) 
              { 
                 JBSx =rs.getString("gps");
                 JBSx="<div id=dd>"+JBSx+"</div>";
                 if(JBx!=null){
                  JBx=JBx+JBSx;

                 }else
                 {
                     JBx=JBSx;

                 }
                     JBSy =rs.getString("recopy");
                     JBSy="<div id=ff>"+JBSy+"</div>";
                     if(JBy!=null){
                          JBy=JBy+JBSy;

                     }
                     else
                     {
                         JBy=JBSy;

                     }
              } 
            } 
            catch(SQLException e) 
            { 
              System.out.println("DropDB Exception :" + e.toString()); 
            } 
//          finally 
//          { 
//            Close(); 
//          } 
          } 

          private void Close() 
          { 
            try 
            { 
              if(rs!=null) 
              { 
                rs.close(); 
                rs = null; 
              } 
              if(stat!=null) 
              { 
                stat.close(); 
                stat = null; 
              } 
              if(pst!=null) 
              { 
                pst.close(); 
                pst = null; 
              } 
            } 
            catch(SQLException e) 
            { 
              System.out.println("Close Exception :" + e.toString()); 
            } 
          } 
      public LOAD() 
      { 
        try { 
          Class.forName("com.mysql.jdbc.Driver"); 
          con = DriverManager.getConnection( 
                  "jdbc:mysql://hl2dm.synology.me:3306/teama", 
                  "abc",""); 

        } 
        catch(ClassNotFoundException e) 
        { 
          System.out.println("DriverClassNotFound :"+e.toString()); 
        }
        catch(SQLException x) { 
          System.out.println("Exception :"+x.toString()); 
        } 

      }  
    public void doGet(HttpServletRequest rq, HttpServletResponse rp) 
                    throws ServletException, IOException{
    JBx=null;
     JBy=null;
    JBSx=null;
    JBSy=null;
        rq.setCharacterEncoding("UTF-8");
//       String gps = rq.getParameter("gps");

        LOAD test = new LOAD(); 
        test.SelectTable(); 
        HttpSession session = rq.getSession();
//session.invalidate();
//        session.removeAttribute("reportx");
        session.setMaxInactiveInterval(3600);      
        session.setAttribute("reportx",JBx);
        session.setAttribute("reporty",JBy);
        rp.sendRedirect(rp.encodeRedirectURL("LOADPOST"));
    }
    public void doPost(HttpServletRequest rq, HttpServletResponse rp) 
                    throws ServletException, IOException{
        doGet(rq, rp);
    }
}

Error message: HTTP ERROR 500

Problem accessing /LOAD. Reason:

    INTERNAL_SERVER_ERROR
Caused by:

java.lang.NullPointerException
    at a.b.c.LOAD.SelectTable(LOAD.java:52)
    at a.b.c.LOAD.doGet(LOAD.java:149)
    at a.b.c.LOAD.doPost(LOAD.java:160)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:511)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1166)
    at com.google.appengine.api.socket.dev.DevSocketFilter.doFilter(DevSocketFilter.java:74)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at com.google.appengine.tools.development.ResponseRewriterFilter.doFilter(ResponseRewriterFilter.java:123)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at com.google.appengine.tools.development.HeaderVerificationFilter.doFilter(HeaderVerificationFilter.java:34)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at com.google.appengine.api.blobstore.dev.ServeBlobFilter.doFilter(ServeBlobFilter.java:61)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at com.google.apphosting.utils.servlet.TransactionCleanupFilter.doFilter(TransactionCleanupFilter.java:43)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at com.google.appengine.tools.development.StaticFileFilter.doFilter(StaticFileFilter.java:125)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at com.google.appengine.tools.development.BackendServersFilter.doFilter(BackendServersFilter.java:97)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:388)
    at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
    at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)
    at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:765)
    at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:418)
    at com.google.appengine.tools.development.DevAppEngineWebAppContext.handle(DevAppEngineWebAppContext.java:94)
    at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
    at com.google.appengine.tools.development.JettyContainerService$ApiProxyHandler.handle(JettyContainerService.java:409)
    at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
    at org.mortbay.jetty.Server.handle(Server.java:326)
    at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
    at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:938)
    at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:755)
    at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:218)
    at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
    at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:409)
    at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:582)
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Answer 1

To answer your question, yes it will cause definite failure.

There is no MySql instance to connect to on AppEngine. You need instead to use Google Cloud SQL.

It goes something like this:

  DriverManager.registerDriver(new AppEngineDriver());
      con = DriverManager.getConnection("jdbc:google:rdbms://instance_name/guestbook");

See: this AppEngine guide for the complete set of steps.

Note: To use the development server with a local MySQL instance, see https://developers.google.com/appengine/docs/java/cloud-sql/developers-guide#using_the_java_development_server