Database Connection Pattern

Question

Hi:
I'm looking for a best practice to centralizing access to the database. All the examples that I have seen on the Sun site and the Internet look a little clumsy. What I'm trying to ask is this. Instead of CODING a connection object, Statment object etc. like the examples provide - every time I make a query. Is there a better way of centralizing make making this code generic.
For example:
I have an object that describes my records say ModelBunny
mBunny.setEars
mBunny.setTail
mBunny.setColor
I have an object that describes all my database queries that I want to execute say DataBunny
dBunny.getBunnyByID
dBunny.getAllBunnies
dBunny.getBunnyByColor
I created a transaction object that allows me to load up multiple sql commands into the transaction object for more complex calls.
I pass the transaction object into a generic connection object that opens, runs the transaction and then closes. For inserts, updates and deletes this pattern works great - I pass back an array of int and let the user know what happened - success/failure.
Here is the root of the issue:
in my generic connection object - I create a query method. Where I pass in a single query statement that returns a - resultset (yes here is my problem).
The resultset is only valid if the connection remains open - then as soon as I close out the connection in my "finally" - I'm done, toast, otherwise - screwed.
I thought of making a method where I can manually close my connection from the calling object - but I want something more brainless where another developer using this framework won't forget and leave the connection dangling.
Is there some way I can process the resultset generically into an arraylist and then pass back the arraylist?
I'm not even certain that this pattern that I'm using is wise. Everybody seems keen on writing the same boiler plate code every time they want to execute a command. I don't think this is good design practice and make the code unmanageable. I'd like some advice or a pointer to something better.
I'm using OracleXE for my test bed. I'd like to leave everything as generic as possible because our platform will likely shift to another DBMS.
Thanks for your help.

Answer 1

FYI: Here is the meat of the generic class that I'm talking about.
public class DbConnection {
private String _urlDbCnn       = "";   // the JDBC url to the database
private String _username       = "";   // a valid username to access the database
private String _password       = "";   // a valid password to access the database
private String _dbDriver       = "";   // a valid JDBC driver
private Connection _cnn            = null; // this will be the active connection
private String _sqlStatement   = null; // this will be the statement to execute against the database
public DbConnection(){
this("oracle.jdbc.OracleDriver",
"jdbc:oracle:thin:@//192.168.15.200:1521/xe",
"usernamehere",
"passwordhere");
} // constructor - nothing
public DbConnection(String nwDbDriver, String nwDbURL,
String nwDbUsername, String nwDbPassword){
this.setDbDriver(nwDbDriver);
this.setUrlDbCnn(nwDbURL);
this.setUsername(nwDbUsername);
this.setPassword(nwDbPassword);
} // constructor - DbDriver, DbUrl, DbUser, DbPassword
private void initializeConnection(){
// try - get database driver
try{
DriverManager.registerDriver (new oracle.jdbc.OracleDriver());
// try - initialize the database connection
try{
this._cnn = DriverManager.getConnection(this._urlDbCnn,
this._username,
this._password);
}catch(SQLException e){
ErrorTrap trap = new ErrorTrap(ErrorTrapMessage.DataConnectionNotIntitialized, e);
} // catch - try and initialize the database connection
}catch(SQLException e){
ErrorTrap trap = new ErrorTrap(ErrorTrapMessage.DataConnectionDriverFailedToLoad, e);
} // catch - try and get database driver
} // method - OpenConnection
public ResultSet executeQuery(DbTransaction nwTransaction){
ResultSet results = null; // batch results are returned as an array of integers
// initialize the database connection
initializeConnection();
// try - access the database connection and execute a batch of statements
try{
// if - check that the connection is open
if (this._cnn.isClosed()== false){
// create a statement object from the connection
Statement sqlQuery = this._cnn.createStatement();
// if - check that there is at least one command present
if (nwTransaction.size() >= 1 ){
// execute the batch success/error results are returned as an int array
results = sqlQuery.executeQuery(nwTransaction.get(0).getCommand());
} // if - check that there is at least one command present
} // if - check that the connection is open
catch(SQLException e){
ErrorTrap trap = new ErrorTrap(ErrorTrapMessage.DataSQLTransactionFailed, e);
} // catch - SQL Query
finally{
// try - close database connection
try{
//if - check that the connection is open
if(this._cnn.isClosed() == false){
// close the database connection
this._cnn.close();
} //if - check that the connection is open
}catch(SQLException e){
ErrorTrap trap = new ErrorTrap(ErrorTrapMessage.DataConnectionNotOpen, e);
} // catch - try and close database connection
} // finally
return results;
} // method - executeQuery
public int [] executeTransaction(DbTransaction nwTransaction){
int [] results = null; // batch results are returned as an array of integers
// initialize the database connection
initializeConnection();
// try - access the database connection and execute a batch of statements
try{
// if - check that the connection is open
if (this._cnn.isClosed()== false){
// create a statement object from the connection
Statement batchStatement = this._cnn.createStatement();
// for - loop through each command added to the transaction
for(DbCommand command:nwTransaction){
// add the sql command for batch execution
batchStatement.addBatch(command.getCommand());
} // for - loop through each command added to the transaction
// execute the batch success/error results are returned as an int array
results = batchStatement.executeBatch();
} // if - check that the connection is open
catch(SQLException e){
ErrorTrap trap = new ErrorTrap(ErrorTrapMessage.DataSQLTransactionFailed, e);
} // catch - SQL Query
finally{
// try - close database connection
try{
//if - check that the connection is open
if(this._cnn.isClosed() == false){
// close the database connection
this._cnn.close();
} //if - check that the connection is open
}catch(SQLException e){
ErrorTrap trap = new ErrorTrap(ErrorTrapMessage.DataConnectionNotOpen, e);
} // catch - try and close database connection
} // finally
return results;
} // method - executeCommands