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B&S RMI

Dhanasekar Dhakshin
Greenhorn

Joined: Jan 19, 2006
Posts: 5
Hi there,

Keep in mind that networking must be entirely bypassed in the non-networked mode
.

In my assignment 'Service' interface extends Remote and all its methods throws RemoteException

ServiceFactory Class get service from service object either by Instantiation or Naming.lookup based on command line argument.

My doubt is even in 'alone' mode my service object implements Remote interface and Service methods also throws RemoteException.

is it violate the condition or not?.

Anybody clear my doubt . . . .

Thanks in advance . . . .
Jeroen T Wenting
Ranch Hand

Joined: Apr 21, 2006
Posts: 1847
You may want to redesign your solution.

My assignment mentions only a DB interface. Of that I created 2 derived interfaces, one for remote and the other for local use.

Classes implementing these interfaces provide the actual access to the database.

So there's a RemoteDB extending DB (though indirectly, I've directly extended DB to include some more functionality like returning an recordset instead of just an array of recordIds).

Neither is ever used directly.
Instead I've 2 more wrappers, representing a remote or local connection, both of them extending an abstract base.
A factory returns either one depending on whether a remote or local connection is requested.
The RemoteConnection intercepts the RMI exceptions and wraps them in a generic DatabaseException which is the same that the LocalConnection does with the IOExceptions returned from the Data class.

So the entire network and standalone modes are transparent to all of the client application except the connect routine, the associated dialog to enter the connection details, and the factory which actually creates the connection object.
All the factory knows is to either create a LocalConnection or an RMIConnection depending on one of the parameters used to call it.





Lots of code removed here of course, things like creating the local DataFile instance from a class retrieved using reflection for example.


42
Josephx Rainerd
Greenhorn

Joined: Apr 27, 2006
Posts: 12
Well , I am reposting after correction.
=============================================


I do appreciate opinion on the following:

My assignmentis B&S. I modelled the server class(RMI and standalone) as

// Parent interface
public interface Server {
public String[] read(long recNo) throws Exception;
..
}

// RMI client
public interface RemoteServer extends Remote,Server {
public String[] read(long recNo)
throws RemoteException,RecordNotFoundException;
...
}

// Standalone server
public class StandAloneServer implements Server {
public String[] read(long recNo) throws RecordNotFoundException { .. }
....
}

So I do ...
Server server = new StandAloneServer (port etc..) ..
or
Server server = Naming.lookup(name etc..) ..

#2
My Database design uses Adapter pattern and does not care if it is Remote or stand alone server.

Thanks
-Joseph
[ April 28, 2006: Message edited by: Josephx Rainerd ]
Dhanasekar Dhakshin
Greenhorn

Joined: Jan 19, 2006
Posts: 5
thanks to all for ur excellent comments and suggestions
Jeroen T Wenting
Ranch Hand

Joined: Apr 21, 2006
Posts: 1847
That's pretty similar to what I did Joseph, except I wrapped my Data class (your Server I guess) in a connection class which holds and controls the Data class as well as the connection details.

My RMIConnection for example has the following:




There is a method declared in the Connection interface which returns the proxy in case of an RMIConnection, the actual Data instance in case of a LocalConnection.

The DecoratedDB and DecoratedDBRemote interfaces both extend the required DB interface, adding some convenience methods.
The proxy wraps the Remote variant in order to rethrow RemoteExceptions as something else so as to present a common interface to the user irrespective of the actual connection type used.
Josephx Rainerd
Greenhorn

Joined: Apr 27, 2006
Posts: 12
Jeroen

Thanks for replying. Your design is good.

I am just curious.., as I understand, you have a connection factory to create either local or remote connection.Local connection uses local data access methods and remote connection uses remote data access methods(which are similar, but coded separately).
The Connection class (returned by factory) still wraps both Local and Remote data access classes.
If a data access enhancement is needed, it needs to be done in both the data access implementations.

Thanks
Jeroen T Wenting
Ranch Hand

Joined: Apr 21, 2006
Posts: 1847
The Connection class is abstract, the local and remote versions derive from it.
Only 2 places (at most) need to change to add another connection type, the factory and the Enum where those types are defined.
There's really no way around that without defining the types outside the application (say in a properties file) and using reflection (which I do employ for some things).


So say I want to replace RMIConnection with SocketConnection, I just change the factory to return a SocketConnection (which I'd have to define) instead of an RMIConnection.

If I want to add another connection type larger changes of course are needed, that's unavoidable.
 
Consider Paul's rocket mass heater.
 
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