Synchronization in DAOs ?

[Hussein Baghdadi]

Hi all.
I have developed a small J2EE application.
to access the database from servlets and EJB, I used DAO pattern.
because we have only one instance of a given servlet, should I consider the synchronization issues in my DAOs ?
given the following code in a servlet's doPost( ) :

  
CustomerDAO custDAO = MySqlDAOFactory.getCustomerDAO( );
int i = custDAO.insertCustomer(customer);

what to do here ?
surroned the previous code with synchronized statement ?
or add the synchronized modifier to each method of MySqlCustomerDAO class ?
or I don't need to modify anything ?
thanks.

[Peter den Haan]

Where your CustomerDAO has no mutable state - i.e. its instance variables consist of collaborators and configuration information that never changes - you do not need to do anything. The code is threadsafe as is.

Any code that modifies state - for example looking up a DataSource in JNDI and storing it in an instance variable - needs to be synchronized.

You certainly do want to avoid putting the JDBC operations themselves inside a synchronized block or synchronized method. That's unnecessary and, since such operations can take a comparatively long time, the lock contention would potentially kill performance.

- Peter
[ September 02, 2004: Message edited by: Peter den Haan ]

[Hussein Baghdadi]

Thanks alot.
but I have some more questions :
1. given MySqlCustomerDAO's insertCustomer( ) method, this method will try to insert a new row in the database, and we have only single servlet with concurrents users, why we don't need to synchronize insertCustomer( ) method (or using a statement) ?
because we rely on the database insolation's level ?
2. assume we don't use DAO in our servlet to access the database, instead of, we will use a method defiened in the servlet class.

  
public int insertCustomer( ) {
  //code to insert data
}
// doPost( ) implementation
this.insertCustomer(name, email);

should I use insertCustomer( ) inside synchronized statement ? or rely on database's isolation level ?
thanks.

[Adeel Ansari]

since you are instantiating your DAO on every request, the synchronized method or a synchronized block in your DAO doesn't make sense.

synchronized works for multiple threads of the same instance. if i am not wrong.

you can instantiate your DAO in servlet.init() method. and then use synchronized blocks inside your update methods of DAO.

tell me if it is not like that. plz