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From Steve McLeod <steve.mcl...@ingena.com.au>
Subject FW: Database Connection in Logic Beans - pooling?
Date Mon, 02 Sep 2002 06:24:25 GMT
There's a couple of pieces missing in my understanding of this:
 
1.	How do you get hold of the DataSource of the ActionServlet subclass?
Is this what getSystemDatabase() does? If so, then how?
2.	Am I right in assuming that the getSystemDatabase() method
instantiates a new Database class, finds the DataSource, then sets a
property with a reference to the DataSource?
 
My initial attempt at an implementation of this goes something like this:
 
package au.com.sunesis.timesheets;
 
import javax.sql.DataSource;
import java.sql.Connection;
import java.sql.SQLException;
 
public class Database {
    private DataSource dataSource;
 
    public Database(DataSource dataSource) {
            // who/what calls this constructor?
        this.dataSource = dataSource;
    }
 
    public static Database getSystemDatabase() {
            // mysterious - what must go in here to make this work?
    }
 
    public Connection getConnection() {
        Connection conn=null;
        try {
            conn = dataSource.getConnection();
        } catch (SQLException e) {
            // we should log this error
            System.err.println("Error obtaining connection from
DataSource");
            e.printStackTrace();
        }
        return conn;
    }
}
 
 
Thanks
 
Steve
 
---
 
 
Here's how I do it:
I defined a Database class with a constructor that takes a Datasource 
object.  It also has a static getSystemDatabase() method and a getConnection

method.  I subclassed the struts ActionServlet and get ahold of its 
DataSource (defined in struts-config.xml) and pass it into my Database 
object.  Then anywhere in the system I can call 
Database.getSystemDatabase().getConnection() to get a connection to the 
database.
 
This also works outside of webapps because the Database class just knows 
about DataSources and not struts stuff.  Also, this lets your logic beans 
not know about servlets or struts which is much cleaner in my opinion.
 
Hope that helps,
Dave
 
-----Original Message-----
From: Steve McLeod 
Sent: Monday, 2 September 2002 10:10 AM
To: 'struts-user@jakarta.apache.org'
Subject: Database Connection in Logic Beans - pooling?
 
I am using:
Tomcat 4.0
Struts 1.0.2
 
The problem
========
 
I have successfully used the Struts database connection pooling in a trial
web app, but as far as I can tell, a reference to the datasource can only be
obtained from within an Action class (or directly within a JSP page but
let's not think about that today).
 
However I would like to have logic beans which handle database access,
rather than have this in the Action class. But I can't get a reference to
the datasource from the logic bean because it doesn't have a ServletContext
to which I can get a handle.
 
I have toyed with various ideas:
- Initialise a logic bean by passing it a reference to the Servlet
- Acquire a connection in the Action class and pass that to the bean
 
But really, I would rather the logic bean know inherently how to acquire a
database connection.
 
My current workaround is to not use the Struts connection pooling, and
rather to manually create a connection each time database access needs to be
done, then destroy it. But this is clearly not suitable for our production
environment.
 
 
The context of my problem
==================
 
I want to use some code like this in a JSP:
 
<jsp:useBean id="abean" scope="page"
class="au.com.sunesis.timesheets.ClientManager" />
<table border="1">
    <tr>
        <th>#</th>
        <th>Client</th>
        <th>Active</th>
    </tr>
<logic:iterate id="clientList" name="abean" property="clients"
type="au.com.sunesis.timesheets.Client">
    <tr>
        <td><bean:write name="clientList" property="clientID"/></td>
        <td><bean:write name="clientList" property="clientName"/></td>
        <td><bean:write name="clientList" property="active"/></td>
    </tr>
</logic:iterate>
 
 
The idea is that ClientManager is used to handle all general database tasks
for the Client bean (which maps to a Client entity in the database).
ClientManager.getClients() connects to the database, creates an ArrayList of
Client objects, one for each row in the database, and returns the ArrayList.
 
ClientManager has other methods, such as:
-         ClientManager.delete(Client c), which deletes the row in the
database entity corresponding to the specified client.
-         ClientManager.findByPrimaryKey(int ID) which returns the Client
which matches the specified ID
-         ClientManager.save(Client c), which stores the client in the
database, creating or updating as necessary
 
So an Action class can also call any of these directly, and it really
shouldn't care about how these work and how they store to/retrieve from the
database. But I can't think of the elegant way to do this and still be able
to use the Struts connection pooling.
 
Any thoughts?
 
Thanks
 
Steve McLeod
 
 
 

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