Runtime - NullPointerException

[January Montague]

I am not quite sure where to start
but I will do my best to not have it turn into ramble.

First I want to check for an "old" open DB connection
and close it if there is one open


Now where my error occurs:
Then in the while (connected == false)
loop, I delete all of the data out of the tables
because I do not want stale data appearing on the GUI.
For some reason this is where is throws my error.

If I take them out it runs fine.
The real strange deal is I have another program
set up to read from a processor the same way
and that one throws no errors at all.
So I am thinking (okay hoping) its just something small I am missing

Thank you very much for all of your time
January

import java.net.*;
import java.sql.*;
import java.util.*;
import java.io.*;
 
public class Example{
 
//SOMEWHWER AT THE BEGINNING OF THE CLASS
 static PreparedStatement psDELtblRtFields;
  static PreparedStatement psVIP_Connection_Down;
   static PreparedStatement psDELETE_tblRtFieldsMsgBlkHeaders;
  static PreparedStatement psDELETE_tblRtFieldsType1;
 

 

public static void processing_loop() {
     //constants read from a config file
 

    ServerSocket echoServer = null;
    Socket clientSocket     = null;
    String IP_ADDRESS       = VIP_IP_ADDRESS;  // VIP computer
    int SOCKET_NUMBER       = VIP_DATA_SOCKET_NUMBER; //constants read from a config file
 
    boolean connected       = false; //variable to help robustness of connection
    boolean socket_error    = false;
 
    //  Writing to MySql Database declarations
    java.sql.Connection conn = null;
 
   String DELETE_tblRtFields = "UPDATE tblRtFields SET gps_sow=0, " +
    "gps_week=0, intVipMode=0,DblOutputPower=0,DblFrequency=0, intVipBit=0, intTxFail=1," +
    "intMonFail=1, intVote_mismatches=0, intVip_voter_fault=1, intAti_error_count=0," +
    "intAti_fault=1, intMystery_msg_count=0, intMystery_msg_fault=1, "+
    "intMissed_msg_count=0, intVip_mer_fault=1, intVip_no_xmit_fault=1, " +
    "strTx_status=0, intTx_outrange=0, intVip_Tx_power_fault=1, intVip_Tx_power_offset=0, "+
    "intMon_bit_results=1, intTx_bit_results=1, dblCurrent_Temp=0, intTemp_color=1, dblMon_power=0, " +
    "strMon_status=0 WHERE ID = 1";
 
    //DONE 12-17-04
    String DELETE_tblRtFieldsType1=" UPDATE tblRtFields SET gps_sow = 0, " +//DONE 12-17-04
"gps_week=0, intModz=0, intNum_of_meas=0, intMeas_type=0 "+
"WHERE ID=1";
//5 total entries
 
String DELETE_tblRtFieldsMsgBlkHeaders = "UPDATE tblRtFields SET gps_sow=0, "+  //DONE 12-17-04
"gps_week=0, strStation_id=0 "+
"WHERE ID=1";
// 3 total entries
 
    String VIP_Connection_Down = "UPDATE tblIcs SET connection_up=0 WHERE connection_id=19";
 
    // main processing starts here
    try {
      // register Database driver
      Class.forName(SQL_DRV);
 
    } catch(java.lang.ClassNotFoundException e) {
      System.err.print("ClassNotFoundException: ");
      System.err.println(e.getMessage());
    } finally {
      try {
        conn.close();
      } catch
        (Exception e) {}
    } // end finally
 

 
    while ( true ) {  // this is the forever loop
      if ( connected == true ) { //old connection - close it
        try{
          clientSocket.close();
          connected = false;
          System.out.println("Closing socket");
        } catch (IOException ey){
          System.out.println(ey);
          continue;
        }//end try
      } //end if connected == true
 

 
      //IT THROWS THE ERROR HERE, IF I TAKE ALL OF THE STUFF OUT
      //(i.e. all of the prepared statements in that 2nd try block)
      //THEN IT WORKS FINE.
 
      while ( connected == false ) {
        try{
try{
 
psDELtblRtFields.executeQuery();
psDELETE_tblRtFieldsType1.executeQuery();
psDELETE_tblRtFieldsMsgBlkHeaders.executeQuery();
psVIP_Connection_Down.executeQuery();
}
catch(SQLException ex){
System.err.println("SQLException for Blanking tblRtFields: " + ex.getMessage());
ex.printStackTrace();
}
 
          // Connect to socket and listen to it
          //CONSTANTS read from a config file
          clientSocket = new Socket(IP_ADDRESS,SOCKET_NUMBER);
          connected = true;
        } catch (IOException e) {
          System.out.println("Exception caught at line 2211 " + e);
          System.out.println("Attempting to make new connection");
         try{
            Thread.currentThread().sleep(2000);
          } catch (InterruptedException es){
            //System.out.println(es);
          }
          if ( killFile.exists() ) {
            System.out.println("VDL killed");
            //WrapperManager.stop(0);
            System.exit(0);
          }
          //continue;
        }//end try socket connection
      } //end while connected == false
 
      while ( connected == true ) {
        // the following code is simply to detect when the socket goes down
        if ( socket_error == true ) {
          socket_error = false; // initialize for next time
          //break out of this loop
          break;
        }
 
        try{
        conn = DriverManager.getConnection(SQL_URL, USERNAME, PASSWORD);
        //SQL statements
 
psVIP_Connection_Down = conn.prepareStatement(VIP_Connection_Down);  //DONE 10-21-04
 
//RtFields
psDELtblRtFields = conn.prepareStatement(DELETE_tblRtFields);  //DONE 10-21-04
        psDELETE_tblRtFieldsType1 = conn.prepareStatement(DELETE_tblRtFieldsType1);
        psDELETE_tblRtFieldsMsgBlkHeaders = conn.prepareStatement(DELETE_tblRtFieldsMsgBlkHeaders);
 

 

          try{
            // make input stream
            is = new BufferedReader
              (new InputStreamReader(clientSocket.getInputStream()));
 
             try{  //get timeout seconds from maintConfigData file
clientSocket.setSoTimeout(SOCKET_TIMEOUT);  //If no data is received from the socket in x amt of seconds...
 }
 catch (SocketException se){
 System.err.println ("Unable to set socket option SO_TIMEOUT");
 }
 
            //OKAY ALL THE CRAP FROM HERE DOWN TO END OF LOOP IS JUST STUFF.............
            // As long as we receive data, keep reading
            while (true) {
             try{
 
//Code here to read from socket and store data
 
              } catch (RuntimeException ex){
                System.out.println("RuntimeException ex: " + ex);
                socket_error = true;
                ex.printStackTrace();
                break;
              }
 

            } // end while True
 
          } catch (IOException e) {
            System.out.println(e);
            //e.printStackTrace();
            break;
          }//end try make input stream
 
}catch (SQLException ex){
System.err.println(
          "SQLException: 2175" + ex.getMessage());
}
 

      } //end while connected == true
    } //end while true Main Loop
 

  }//end processing_loop()
 
public static void main(String args[]){
Example ex = new Example();
ex.processing_loop();
}
 
}

[Ernest Friedman-Hill]

Hi,

Welcome to JavaRanch!

The variable "psDELtblRtFields" is null until the statement

psDELtblRtFields = conn.prepareStatement(DELETE_tblRtFields);

is executed. But your call to "psDELtblRtFields.executeQuery()" occurs a few dozen lines earlier in your program than does the prepareStatement call, so the first time that executeQuery() is called, psDELtblRtFields is null and you get a NullPointerException. Makes sense, right?

You might simply enhance that "while (connected == false)" to include a "conn == null", as well. But you're really going to have to manage things a bit more carefully. The PreparedStatements are in static variables, but the Connection is in a member variable; and you're re-opening the database connection without ever closing the old connection, or closing the PreparedStatements, or anything.

[January Montague]

But your call to "psDELtblRtFields.executeQuery()" occurs a few dozen lines earlier in your program than does the prepareStatement call, so the first time that executeQuery() is called, psDELtblRtFields is null and you get a NullPointerException. Makes sense, right?

Ya for sure.
That is kinda what I thought,
the only real confusing part is I have anohter
program doing the same thing, but connected to a different processor.

I will work with your advice for
now and see how far I can get.
I am new to JDBC and still learning as I go along.

Thank you for your reply
and when I get this bugger figured out
I will post another reply

Any other advice would be awesome
if anything else comes to mind.

Thanx
January