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From musky <musk...@gmail.com>
Subject Re: Using derby as a chat server
Date Thu, 14 Feb 2008 16:11:46 GMT

i solved it it was because of:
id=mc.returnflag();

sorry for this.


musky wrote:
> 
> i have the following code fao a thread that will select from a table
> periodically.
> here it is:
> import java.util.Timer;
> import java.util.TimerTask;
> import java.sql.*;
> /**
> * Simple demo that uses java.util.Timer to schedule a task to execute
> * once 5 seconds have passed.
> */ public class TestTime {
> 	  DBClass dbobject1=new DBClass();
> 	  MainClass mc;
> 	  Statement stmt;
> 	  static Connection conn=null;
> 	  PreparedStatement pstmt=null;
> 	  ResultSet rs=null;
> 	  int id=0;
> 	  
> public static void main(String[] args) throws Exception {
> TestTime t = new TestTime();
> 
> //MainClass mc=new MainClass();
> DBClass dbobject1=new DBClass();
> conn=dbobject1.createConnection("ChatDB1");
> t.stmt = conn.createStatement();
> try
> {
>   t.stmt.executeUpdate( "DROP TABLE chattable" );
>   System.out.println(
>     "Table chattable was removed.");
> }
> catch ( Exception e ) {          
> /* don't care */ }
> 
> try
> {
> 
> // may need modification for your database
>   t.stmt.executeUpdate( "CREATE TABLE chattable(TID INT,Tchat VARCHAR
> (255))" );
> 
>   System.out.println(
>     "Table chatable was created.");
>   
>   
>   
>  
> }
> catch( Exception e ) 
> {
> 	System.out.println("could not create chattable"+e);
> }
> 
> 
> try
> {
> t.stmt.executeUpdate("insert into chattable values(0,'HI')");
> System.out.println("INSERTED");
> t.stmt.executeUpdate("insert into chattable values(1,'HI MAN')");
> System.out.println("INSERTED");
> 
> t.stmt.executeUpdate("insert into chattable values(2,'HI MAN HOW ARE
> YOU')");
> System.out.println("INSERTED");
> }
> catch( Exception e ) 
> {
> 	System.out.println("could not insert into chattable"+e);
> }
> 
> 
> 
> 
> try { t.stmt.close(); }
> catch( Exception e ) {}
> 
> 
> 
> t.execute();
> System.out.println("Main Method is finishing");
> 
> } 
> 
> private void execute() throws Exception {
> System.out.println(" Tasks scheduled");
> int initialDelay = 1000; // start after 30 seconds
> int period = 2000; // repeat every 5 seconds
> Timer timer = new Timer();
> System.out.println(" Timer set");
> 
> 
> //dbclass db=new dbclass();
> 
> timer.scheduleAtFixedRate(new TimerTask ()
> {
> public void run()
> {
> System.out.println("Task Run");
> //conn=dbobject1.createConnection("ChatDB1");
> 
> 
> try
> {
> 	id=mc.returnflag();
> 	//System.out.println(id);
> 	  // System.out.println("Before ExecuteQuery");
> 
>    pstmt=conn.prepareStatement("select * from chattable");
>   //pstmt.setInt(1,id);
> 
>   rs=pstmt.executeQuery();
>   
>   while(rs.next())
>    {
> 	   String str=rs.getString(2);
> 	   int str2=rs.getInt(1);
> 	   System.out.println(str2+"          "+str);
>    }
> 	
>   
> }
> catch ( Exception e ) {System.out.println("mhjfdshmnjh  "+e);}
> 
> }
> }, initialDelay, period);
> }
> }
> 
>  am getting nullpointerexception.
> 
> please help.
> thanks
> 
> 
> Donald McLean-3 wrote:
>> 
>> Yes, you would use a timer. You'll have to experiment with the timing
>> (too
>> often and it thrashes).
>> 
>> You would select any message newer than the last message that was
>> retrieved.
>> 
>> On Feb 13, 2008 7:49 PM, musky <muskvar@gmail.com> wrote:
>> 
>>>
>>> then how do i have a thread periodically select the latest message from
>>> the
>>> table?
>>> should i use a timer or something
>>>
>>> Donald McLean-3 wrote:
>>> >
>>> > You might also want to have a messageID and maybe a messageTimestamp.
>>> >
>>> > If everyone is connecting directly to the database server then you're
>>> just
>>> > going to have to do a select periodically to see if anyone posted
>>> anything
>>> > new.
>>> >
>>> > I don't know what kind of connection limits a database server has, but
>>> if
>>> > your target audience is large enough, your architecture could break
>>> down
>>> > (or
>>> > even just bog down).
>>> >
>>> > On Feb 13, 2008 10:06 AM, musky <muskvar@gmail.com> wrote:
>>> >
>>> >>
>>> >> also i dont want to use any sockets.
>>> >> all the chat clients connect to the database server.
>>> >>
>>> >> musky wrote:
>>> >> >
>>> >> > i want to use derby as a chat server,
>>> >> > my idea is to insert whatever a user types into a table in the
>>> >> > database.This table can have two fields UserID and the
>>> >> > message(VARCHAR).how do i convey the inserted message to the other
>>> >> party??
>>>
>>>
>> 
>> 
> 
> 

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