Design issues

[dhana sekar]

Hello All,
I have a doubt regarding design which iam following
* In order to make all the public methods of Data.java to be avilable in the RemoteClient
I have an interface DataInterface.java which will have all the public method of Data.java
* Now i have one more interface which will extend
DataInterface and Remote interface of rmi, Which named as RemoteDataInterface.java
* Now i have two implementation class as follows
one for remoteAccess and another for localAccess
1. RemoteDataAccess extend UniCastReportObject implements RemoteDataInterface

2. LocalDataAccess implements DataInterface
* Finally i have a ClientFactory class which has a
method as follows
Public class ClientFactory
{
DataInterface getConnection()
{
//will return RemoteDataAccess
or LocalDataAccess based on the user choice
}
}

Guys those who completed JD pleasec give me ur valid comments on my design so that i can proceed.
thanks & regards
-dhana

[dhana sekar]

Dear All,
Please go through the above Design of mine
and give me ur valuable feedback.

thanks & regards,
dhana

[Mark Spritzler]

Looks good. I'd only change one thing and this is nitpicking, so you can ignore it if you wish.

DataInterface getConnection()

I'd call this method getDataAccess, or something along those lines. When I think of getConnection, I think of a connection object to a remote server.
I think your Factory that gets bound to RMI will have a method called this.
Mark

[dhana sekar]

Hi Mark,
Thanks Mark for valuable feedback. Now i did a small in the above design as follows.
*LocalDataAccess extends Data implements DataInterface
* Incase of ClientFactory class i have a method getConnection(String mode), Because if the mode is remoteClient then i do a Naming.lookUp() and return the DataInterface to the caller where it will be typecasted as RemoteDataAccess.
Mark is it ok waiting for ur feedback.
-regards
dhana

[Mark Spritzler]

LocalDataAccess extends Data implements DataInterface

why did you do that? It looked so good before.

Incase of ClientFactory class i have a method getConnection(String mode), Because if the mode is remoteClient then i do a Naming.lookUp() and return the DataInterface to the caller where it will be typecasted as RemoteDataAccess.

I think the key word in your Factory class is par tof it's name. "Client" client to me says nothing about connections. Now remote does. No don't change the name of the class. Make the method called getDataAccess. Because what it returns is an instance of a class that implements DataAccess interface.
This is even though the ClientFactory could possibly do a naming.lookup() call.
Mark

[dhana sekar]

Hi Mark,
As usual ur right. Now iam clear LocalDataImpl only implements the DataInterface .
Here in the LocalDataImpl class iam just instanciating the Data's object in the constructor. And using it to invoke the method's of the Data class. Is it ok.
thanks & regards,
-dhana

[Mark Spritzler]

Here in the LocalDataImpl class iam just instanciating the Data's object in the constructor. And using it to invoke the method's of the Data class. Is it ok.

Yes.
Mark

[dhana sekar]

Hi Mark,

Hope u might have had a great weekend.

I was bit confused with my design. Here the main purpose of having the LocalDataAccess class is to make use of the Factory Pattern in the
clientside to select the clientMode(Remote or Local). Now i have plans to change the design as follows. Kindly please go through this and give me valuable feedback.

* DataInterface which has all the public method of Data class. This also extends Remote interface of java.rmi.
* I have a RemoteImplementation class RemoteDataImpl which extends UnicastRemoteObject and implements DataInterface.
* I have DataAccessImpl.class which extends Data and have the implementation of lock()
unlock() ceriteriaFind() of Data class. ie iam using the Data.class as it is with out doing any change. Here DataAccessImpl implements DataInterface( this has one or two method like modifyRec(RecNo,seat) which is not there in the Data class which will be usefull for me in case of modifying the record.

awaiting for ur feedback.
thanks & regards.
-rameshkumar.

[Bhuvan mehra]

hi!
i didn't start my design yet because of one problem. pls. go through that.
topic heading is
"instruction - writing Data Client. "WAITING FOR RESPONSE"
written by Bhuvan.
pleas give my your opinion.
thanks and regards,
Bhuvan.

[Mark Spritzler]

this has one or two method like modifyRec(RecNo,seat) which is not there in the Data class which will be usefull for me in case of modifying the record

If like it. I would remove the modifyRec. The only reason, is later on on the client side you can create a DataAccessFacade, this facade has only a couple of methods. Like bookSeats, or searchFlights. In these methods you can use an object that implements DataAccess, that you use. You could even include your modifyRec method as a private method of this Facade, and use it.
The Facade pattern hides the complexity of a system, like the server from the client. Then the client doesn't need to know anything about the Server or the Data classes. It just knows, Hey I want to book a seat and I have a class that is a facade that I can call one method on, and it will do it for me, and I can trust that it works, and It is nice and neat and clean.
Mark

[dhana sekar]

Hi Mark ur right and i agree with the design change u advised. I have the following reasons
why i have bookSeat() and findFlight() in the DataInterface.
1. I have plans to implement Adapter pattern and Factory Pattern in my design. To achive this i have a common Interface(DataInterface) for both serverImpl and
localImpl.
2. I dont want to change the Data.java so
iam extending Data.java in my DataAccess.java and also implementing DataInterface. Here i should have reason for implementing the DataInterface while also extending Data class thats why i have bookSeat(), findFlight() in the DataInterface.

If i go for facade pattern then i think i cant use Factory pattern(iam not sure).
So please guide like which one is best. waiting for ur reply.
thanks & regards
dhana

[Mark Spritzler]

If i go for facade pattern then i think i cant use Factory pattern(iam not sure).

Yes you can. The constructor for the Facade takes an instance of DataAccess, the interface. This way you have a factory that creates a remote or local instance and then passes that into the Facades constructor and the Factory returns the Facade. The factory makes all this for you. That's why they call it a factory.
Mark

[dhana sekar]

Hi Mark ,
Following is my understanding about what u said above. Please go throught that and correct me if iam wrong.
* Using DataAccessFactory i will get an instance of the DataInterface.
* There will a AccessFacade which will have a constructor that takes DataInterface as an
argument. Here in AccessFacade there are two methods BookSeat() flightSearch() which intern uses the DataInterface's methods(like getRecord(),modify() etc..) to book the seat and search the Flight info.

thanks & regards,
-dhana

[dhana sekar]

Hi Mark,

I have one more thing to get cleared. As per the current desing changes.
* The DataInterface will contain only the methods of Data class. If this is the condition then mark i have a doubt that in the DataAccessImp.java( Which extends Data.java, Has the functionality of lock,unlock,criteiriaFind) what is the need of implementing the DataInterface.java which has the methods of Data class, With out implementing this i can't use the Factory pattern in case of mode(local, remote) selection. That's why i plan to have BookSeat(), flightSearch() in the DataInterface. Now iam in a bit confusion so Mark help me to proceed further.
thanks & regards,
dhana

[Mark Spritzler]

OK, if you have a model like this
DataAccess interface has all public methods of Data class, methods throw Exception, it extends Remote.
DataAccessRemote extends UnicastRemoteObject implements DataAccess, Unreferenced. Unreferenced is an interface for handling stale clients. Methods Throw RemoteException and sometimes DatabaseException
DataAccessLocal implements DataAccess. Methods throw Exception, or DatabaseException.
DataAccessFactory has two overloaded methods called getAccess. One takes a host string(remote) the other nothing(local). In mine it just returns DataAccess.
In my main class I call the factory get the DataAccess, create an instance of the Facade passing it the DataAccess class(which might be Remote or Local, it doesn't matter.)
Now I am off and running with my Facade.
Hope that clears things up for you.
Mark

[Ramesh kumaar]

Hello Mark,

Iam highly impressed with the above design. But have some issues to be discussed
Mark in the above design DataAccessLocal.java implements DataAccess. As per the above design i have to instantiate the Data class and call the appropriate methods and i have to fill the functionally for lock(), unlock(), cretriafind() in the Data.java. Instred of this if i extend Data.java in DataAccessLocal.java i can provide the implementation for lock(), unlock(), cretriaFind() in the DataAccessLock.java itself where i wont touch the Data.java. But If i do the above then there is no need for me to implement DataAccess interface because this has only the method's of Data.java. If i dont do this i cant make use of factory pattern. So to solve these problems can i introduce some new methods like bookSeat(), flightFind() in the DataInterface
and i can give a reason for implementing DataAccess while extending Data.java and also i can use Factory, Adapter,facade patterns. I need ur comments on this design changes.
thanks & regards,
-rameshkumar

[Laudney Ren]

Ramesh:
I know what you are worrying about. To solve your problem of not being able to use factory pattern, simply changes the signature of Data into "implements DataAcess". Then, both DataAccessLocal(indirectly, by extending Data) and DataAccessRemote(directly) implements DataAccess. So, you can use factory pattern.
Laudney