RMI

What is the role of Remote Interface in RMI?

The Remote interface serves to identify interfaces whose methods may be invoked from a non-local virtual machine. Any object that is a remote object must directly or indirectly implement this interface. Methods that are to be invoked remotely must be identified in Remote Interface. All Remote methods should throw RemoteException. 

What is the role java.rmi.Naming Class?

The Naming class provides methods for storing and obtaining references to remote objects in the remote object registry. 

What is RMI?

Remote Method Invocation (RMI) is the process of activating a method on a remotely running object. RMI offers location transparency in the sense that it gives the feel that a method is executed on a locally running object. 

What is the basic principle of RMI architecture?

The RMI architecture is based on one important principle: the definition of behavior and the implementation of that behavior are separate concepts. RMI allows the code that defines the behavior and the code that implements the behavior to remain separate and to run on separate JVMs. 

What are the layers of RMI Architecture?

The RMI is built on three layers. 
a. Stub and Skeleton layer
This layer lies just beneath the view of the developer. This layer intercepts method calls made by the client to the interface reference variable and redirects these calls to a remote RMI service. 

b. Remote Reference Layer. 
This layer understands how to interpret and manage references made from clients to the remote service objects. The connection is a one-to-one (unicast) link. 

c. Transport layer 
This layer is based on TCP/IP connections between machines in a network. It provides basic connectivity, as well as some firewall penetration strategies. 

What is meant by binding in RMI?

Binding is a process of associating or registering a name for a remote object that can be used at a later time to look up that remote object. A remote object can be associated with a name using the Naming class\'s bind or rebind methods. 

What is the difference between using bind() and rebind() methods of Naming Class?

bind method(String name) binds the specified name to a remote object while rebind(String name) method rebinds the specified name to a new remote object,any existing binding for the name is replaced. 

When is AlreadyBoundException thrown and by which method?

AlreadyBoundException is thrown by bind(String name) method when a remote object is already registered with the registry with the same name. 
Note: rebind method doesn\'t throw AlreadyBoundException because it replaces the existing binding with same name. 

How to get all the registered objects in a rmiregistry?

Using list method of Naming Class.

Can a class implementing a Remote interface have non remote methods?

Yes. Those methods behave as normal java methods operating within the JVM.

What is the use of UnicastRemoteObject in RMI?

The UnicastRemoteObject class provides support for point-to-point active object references using TCP streams. Objects that require remote behavior should extend UnicastRemoteObject. 

What does the exportObject of UnicastRemoteObject do?

Exports the remote object to make it available to receive incoming calls, using the particular supplied port. If port not specified receives calls from any anonymous port. 

What is PortableRemoteObject.narrow() method and what is used for?

Java RMI-IIOP provides a mechanism to narrow the the Object you have received from from your lookup, to the appropriate type. 
This is done through the javax.rmi.PortableRemoteObject class and, more specifically, using the narrow() method. 

What are the two important TCP Socket classes?

Socket and ServerSocket. ServerSocket is used for normal two-way socket communication. Socket class allows us to read and write through the sockets. getInputStream() and getOutputStream() are the two methods available in Socket class.

What is RMI Registry ?

A registry is a remote object that maps names to remote objects. A server registers its remote objects with the registry so that they can be looked up. When an object wants to invoke a method on a remote object, it must first lookup the remote object using its name. The registry returns to the calling object a reference to the remote object, using which a remote method can be invoked.