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Re: Help Needed with Connection Pooling for Java Swing Based - Mailing list pgsql-jdbc

From Scot P. Floess
Subject Re: Help Needed with Connection Pooling for Java Swing Based
Date
Msg-id 3E82E9E8.7060802@mindspring.com
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In response to Re: Help Needed with Connection Pooling for Java Swing Based  (Shanmugasundaram Doraisamy <shan@ceedees.com>)
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Shan:

Can't you simply "associate" the connection with the window and when it closes, return it at the pool?   You could have a helper class who acts as a window listener and contains a connection.  When the window closes, the helper class will be called - at that time have the helper class return the connection to the pool.

Scot

Shanmugasundaram Doraisamy wrote:
Dear Derek, Scott & Barry,	   Thank you for your replies.  But, when I give the system.exit call
the whole application is closed.  This is not what I want to do.  I just
want to close only that particular form/ window alone and return the
connection to the pool.  Please let me know how this can be achieved. 
Thanking you,

Yours sincerely,

Shan.

On Thu, 2003-03-27 at 04:09, Scot P. Floess wrote: 
Derek:

I see what you mean.

Regarding needing to call System.exit...my guess is the Swing/AWT 
threads are user threads (as opposed to daemon) and that is why one must 
call System.exit()...

Scot

Derek S wrote:
   
Pardon my inaccuracy.  I should have said "Realizing" instead of 
instantiating.  "Realizing" is the name that the AWT developers gave 
to the process  (which is encapsulated in the AWT's component 
implementation) of actually allocating the system resources needed to 
display the GUI widgets.  Typically, it happens when you call pack or 
setVisible(true) on a Window, Frame or Dialog. When a component is 
realized, it checks to see if the dispatcher thread is running, and if 
not, starts it.  Depending on what you're using, it may also start 
other threads to support features like the Pluggable Look and Feel and 
so on.  As far as I know, it's only possible to have one AWT Event 
Dispatch thread.

Bringing us back to the original topic, Once the AWT threads are 
running, it's basically hit-or-miss whether the app will stop unless 
System.exit is explicitly called or you set the default close 
operation on your frame to EXIT_ON_CLOSE (which just calls System.exit 
for you), so this has nothing to do with JDBC or PostgreSQL's driver.

Scot P. Floess wrote:
     
Derek:

Are you sure instantiating a Swing component launches a new thread?  
Simply instantiating 2 JButtons will launch 2 threads?  I don't think 
that is the case.

Derek S wrote:
       
Instantiating any Swing component does in fact start a new thread - 
the AWT Event Dispatch thread.  My experience with it has been that 
this thread quite often doesn't terminate the way you might expect 
when the main method ends.  This is a well known issue that Swing 
and AWT programmers simply have to deal with and has absolutely 
nothing to do with JDBC.  Generally speaking, all Swing/AWT based 
applications call System.exit when they are finished doing whatever 
it is they do in order to ensure that the AWT Event Dispatch thread 
shuts down properly.

Barry Lind wrote:
         
I just ran your test case and everything seems to be working 
correctly as far as I can tell.  The program creates one and only 
one connection to the database.  I don't see multiple connections 
created as you are reporting.

I don't know anything about swing, but it is clear that the code 
for swing you have below isn't correct.  Because with this swing 
call the program doesn't exit.  It seems the swing code is starting 
some other threads that are running and thus the main program 
doesn't exit until those threads stop running (and I don't know 
what swing calls are necessary to stop the swing threads from 
running).

So with the swing call in place I have to ctrl-C to stop the app 
from running, but from the jdbc side of things everything seems to 
be working correctly.

Perhaps I don't understand the problem you are seeing?

thanks,
--Barry


Shanmugasundaram Doraisamy wrote:
           
Dear group,

We are having some problems when using JDBC Connection Pool using 
Postgrsql Jdbc3PoolingDataSource.

The Pool behaves fine if there is no Swing Component in the Program.
If there is a swing Component ,then the connection seems to be not 
returning to the pool and calling for an additional instance of 
the class leeds to the creation of fresh Connection objects ,at 
times it even exceeds the maximum number allowed in the pool.
If we go for System.exit(0);(Killing) then only the Connection is 
returned .

But if we comment the swing component line (here in the attached 
Program a JOptionPane is Used) then the pool behaves fine.


Herewith Iam attaching a Program which is behaving as detailed.

Any Help is Welcome.

##################################################################


##################################################################

/** ConPool.java** Created on 26 March 2003, 11:54*/

/**** @author  naks from vpsd,Erode*   */
import org.postgresql.jdbc3.*;
import java.sql.*;

public class ConPool {      Jdbc3PoolingDataSource source = null;   private Connection conn = null;      /** Creates a new instance of ConPool */   public ConPool() {          }      /** Setting the Pool which intializes the Pool to 2. */   public void setPool() {       // DataSource initialization       System.out.println("setPool()");       try {           System.out.println("setting pool");           // constructs a pool only when source is not assigned.           // this will prevent problems if the same pool is set 
more than           // one time           if (source == null) {               source = new Jdbc3PoolingDataSource();               // DataSource configuration.                     source.setServerName("192.168.0.51");       source.setDatabaseName("kec_test_pool");       source.setUser("venbro");       source.setPassword("venbro");       source.setMaxConnections(2);                              } else {               System.out.println("pool is set");               return;           }       } catch (Exception loException) {           // logger.logToFile(loException);           loException.printStackTrace();       }
   } //End of setPool method         /**    * Method inserts data to a table "test" which is like    * create table test (param1 varchar(2),param2 varchar(2)) ;        */    public int insertDatas(){          int count=-1;            try{              conn=source.getConnection();
     PreparedStatement st = conn.prepareStatement("INSERT INTO 
test values('P1','P2')");          count = st.executeUpdate();
     st.close();          conn.commit();     conn.close();        }   catch (SQLException ex) {      count=0;     ex.printStackTrace();   }      return count;   }//End of Insert Method             public static void main(String args[]){                     ConPool cp=new ConPool();       cp. setPool();       int sucess_flag=cp.insertDatas();       System.out.println("Sucess"+sucess_flag);              /**         * Upto this level the Connection pooling is working fine .         * But if this Swing Component is added then it creates 
new Connection         * which is even more than the intial connection of the 
pool..        *  We have to kill the application (System.exit(0))to 
remove the Connection        ** But on commenting line :105 "Swingline " the Pool is 
working fine..                */       
javax.swing.JOptionPane.showMessageDialog(null,"VENBRO-ERODE","MESSAGE",1);// 
Swing line 105               }
}//End of the class
##########################################################################################

###########################################################################################


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-- 
Scot P. Floess - 27 Lake Royale - Louisburg, NC  27549 - 252-478-8087

Open Source Home Page
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http://jwaretechniques.sourceforge.net

Open Source Project Host
-----------------------------------------------
http://sourceforge.net/projects/javapim
http://sourceforge.net/projects/jplate
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-- 
Scot P. Floess - 27 Lake Royale - Louisburg, NC  27549 - 252-478-8087

Open Source Home Page
--------------------------------------
http://javapim.sourceforge.net
http://jplate.sourceforge.net
http://jwaretechniques.sourceforge.net

Open Source Project Host
-----------------------------------------------
http://sourceforge.net/projects/javapim
http://sourceforge.net/projects/jplate
http://sourceforge.net/projects/jwaretechniques

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