connection problem

[Gowher Naik]

i am trying to save all connection objects in hashmap in jdbc.but when ever i try to put connection object in map it does not store actual object.
my code is like this

Connection c=DriverManager.getConnection(url,"sa", "sql");
java.util.Map conPool=new HashMap();
conPool.put(c,"01");

but when i print HashMap it gives op as follows
sun.jdbc.odbc.JdbcOdbcConnection@c2ea3f 01

when according me it should print c 01
so how i will store c in hash map.plz help
thanks

[Sarath Mohan]

It's printing correctly!...

Connection object doesn't have a proper toString() method overridden. So it will print the default implementaion of toString method of Object class.

[Jeanne Boyarsky]

Gowher,
I agree with Sarath. Just out of curiousity, why are you writing your own connection pool?

Also you probably want conPool.put("01" ,c); instead of conPool.put(c,"01");

That way you can look up the connection by the key ("01").

[Arun Prasath]

We can keep either of them as the Key in Map. As every connection instance is unique, that can be kept as key in the Map.
I use Connection as key and the status of the connection as the value in my Connection Pool.

Originally posted by Jeanne Boyarsky:
Gowher,
I agree with Sarath. Just out of curiousity, why are you writing your own connection pool?

Also you probably want conPool.put("01" ,c); instead of conPool.put(c,"01");

That way you can look up the connection by the key ("01").

[Adeel Ansari]

Why not implementing your connection pool as a queue.

The real connection pool should have some properties like,
- shrink
- extend


Now, how are you getting the connection from Map? By passing the connection object as a key? It means you already have the connection, you are not getting it from Map, right? So, what are you getting from the Map? Are you getting the status of that particular connection? Where are your connections reside?

[Arun Prasath]

Now, how are you getting the connection from Map?
We call by DBConnectionPool.getConnection().
All the implementation is hided inside this method.

By passing the connection object as a key?
No
It means you already have the connection, you are not getting it from Map, right? So, what are you getting from the Map? Are you getting the status of that particular connection? Where are your connections reside?

We store the predefined amount of connection objects in a Map. We store the availability of the connection object as the Key(true/false). When the user requests for a new connection, We iterate over the map to get the first available connection and return the connection after changing its status(false).
When connection is released from pool, we change its status to be available. (true).

hope I am clear now..

[Adeel Ansari]

Sorry mate, I couldn't understand you. You said in your previous post that you are using connection object as key, and now you are saying that you are using availablity of connection as a key (true/false). These are two different things. As true/false is not unique, how can you use it as a key.


Iterate over a map until a free connection is found. Its not at all a good idea. Why not implement data structure like queue or stack. Queue would be better.

[Adeel Ansari]

Originally posted by Arun Prasath:
We call by DBConnectionPool.getConnection().
All the implementation is hided inside this method.

This one is clear to me, and now i got you.

[Arun Prasath]

Sorry for the confusion. The key is Connection. Value is Status of availability of Connection.
I have added the code here..

  public Connection getConnection() throws SQLException, IOException
  {
    Connection conn = null;
    Set connections = Collections.synchronizedSet(connectionMap.keySet());
    Iterator iterator = connections.iterator();
    synchronized (connections)
    {
      while (iterator.hasNext())
      {
        conn = (Connection) iterator.next();
        Boolean isUsed = (Boolean) connectionMap.get(conn);
        if (isUsed == Boolean.FALSE)
        {
          //We have found an unused connection.
          //lets test this connection by issuing a test query.
          try
          {
            if (conn.isClosed())
            {
              System.out.println("Connection is Closed!@!!!!!");
              connectionMap.remove(conn);
              conn = getNewConnection();
            }
          }
          catch (SQLException e)
          {
            //problem with connection. so remove it.
            e.printStackTrace();
            connectionMap.remove(conn);
            try
            {
              conn = getNewConnection();
            }
            catch (IOException ex)
            {
              System.err.println("Error in getting connection " + ex);
            }
          }
          //Update the Hashtable to show that this connection is being used.
          connectionMap.put(conn, Boolean.TRUE);
          iUsableConnections--;
          return conn;
        }
      }
    }
    //If code reached this block, then there are no free connections.
    //so we make a new connection and put inside hashmap.
    System.out.println("**********Existing Size of Pool->"
        + connectionMap.size());
    System.out.println("********** Increasing Size of Pool by 1");
    if (connectionMap.size() < iMaxConnections)
    {
      conn = getNewConnection();
      connectionMap.put(conn, Boolean.TRUE);
      synchronized (conn)
      {
        iUsableConnections--;
      }
      return conn;
    }
    else
    {
      //Maximum size is reached in connection pool. return Null.
      System.err.println("Connection Pool Reached Maximum size. "
          + connectionMap.size());
      return null;
    }
  }  
  /**
   * This function releases the connection into the pool.
   * 
   * @param connection
   */
  public void releaseConnection(Connection connection)
  {
    if (connection != null && connectionMap.containsKey(connection))
    {
      synchronized (connection)
      {
        iUsableConnections++;
      }
      //set the used flag by setting it to false.
      connectionMap.put(connection, Boolean.FALSE);
    }
  }
 

[ March 29, 2005: Message edited by: Arun Prasath ]

[Arun Prasath]

Originally posted by Adeel Ansari:
Why not implement data structure like queue or stack. Queue would be better.

Now I think that implementing connection pool as a Queue would be much more easier than what I have done. Thanks for pointing it though..