DAO pattern 2004-11-21 - By Ananthalakshmi Subramaniyam
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Hi,
Normally, it is best practice to handle Transaction demarcation outside of
DAO, in order to demarcate Transaction between multiple DAOs. This approach
is more flexible.
For example,
public class UserTransaction {
Connection conn = null;
String strUser = null;
String strDbUrl = null;
String strDbUser = null;
String strPassword = null;
public UserTransaction(String strURL, String strUser,
String strPassword) {
this.strDbUrl = strURL;
this.strDbUser = strUser;
this.strPassword = strPassword;
}
public void beginTransaction(...) {}
public void endTransaction(...) {}
public Connection getConnection() {return connection;}
public void commit() {}
public void rollback() {}
}
public class MyDAOFactory {
public static UserTransaction transaction = null;
public static final String DRIVER=
"COM.cloudscape.core.RmiJdbcDriver";
public static final String DBURL=
"jdbc:cloudscape:rmi://localhost:1099/CoreJ2EEDB";
public static final String USER ="user";
public static final String PASSWORD = "pwd";
public static UserTransaction getUserTransaction() {
if(transaction == null ) {
UserTransaction transaction = new UserTransaction
(DRIVER,DBRUL,USER,PASSWORD);
}
return transaction;
}
...
public AccountDAO getAccountDAO();
}
public class AccountDAO {
public void credit() {
UserTransaction transaction =
MyDAOFactory.getUserTransaction();/use existing user transaction or
create new one.
Connection connection = transaction.getConnection();
Statement stmt = connection.createStatement(sqlQuery);
//do the operations.
}
public void debit() {}
...
}
In Caller class,
MyDAOFactory daoFactory = new MyDAOFactory();
UserTransaction transaction = MyDAOFactory.getUserTransaction();
transaction.beginTransaction();
AccountDAO accountDAO = daoFactory.getAccountDAO();
try {
accountDAO.credit();
accountDAO.debit();
...
transaction.commit();
} catch(myDAOException ex) {
transaction.rollback();
}
transaction.endTransaction();
The above approach is helpful in both DAO demarcated Transaction and
caller demarcated transaction. ie, in DAO demarcated methods, you may have
the following implementation,
public void autonomousCredit() {
UserTransaction transaction =
MyDAOFactory.getUserTransaction();/use existing user transaction or
create new one.
transaction.beginTransaction();
Connection connection = transaction.getConnection();
Statement stmt = connection.createStatement(sqlQuery);
try {
//do the operations.
transaction.commit();
} catch(Exception ex) {
transaction.rollback();
}
transaction.endTransaction();
}
Thanks,
H.Ananthalakshmi.
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