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Synchronization in DAOs ?

Hussein Baghdadi
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Joined: Nov 08, 2003
Posts: 3479

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( ) :

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
author
Ranch Hand

Joined: Apr 20, 2000
Posts: 3252
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
clojure forum advocate
Bartender

Joined: Nov 08, 2003
Posts: 3479

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.

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

Joined: Aug 15, 2004
Posts: 2874
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
 
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