The UnicastRemoteObject Class

This class is the base class for most of the user defined remote objects. It defines a non-replicated remote object whose references are valid only while the server process is alive. It provides support for point-to-point active object references using TCP streams. This class can be used to create and export remote objects. The remote object can be exported implicitly by extending the UnicastRemoteObject , or it can be done explicitly with a call to the exportObject() method of the same class. If UnicastRemoteObject is not extended, the implementation class must provide correct implementation of the hashCode(), equals(), and toString(), so that they behave appropriately for remote objects.

Methods

• public static RemoteStub exportObject(Remote obj) - Exports the specified remote object to make it available to receive incoming calls, using an anonymous port.

• public static Remote exportObject(Remote obj, int port) - Exports the specified remote object to make it available to receive incoming calls, using the particular supplied port.

• public static Remote exportObject(Remote obj, int port, RMIClientSocketFactory csf, RMIServerSocketFactory ssf) - Export the remote object to make it available to receive incoming calls, using a transport specified by the given socket factory.

• public static boolean unexportObject(java.rmi.Remote obj, boolean force) - This method makes the remote object unavailable for incoming calls. If the force parameter is true, the object is forcibly unexported even if there are pending calls to the remote object.

The Naming Class

The java.rmi.Naming class provides several methods that can be used to interact with the remote object registry. The methods can be used to register and query for remote objects. An object is requested by its name, so all names in a particular registry must be unique.

Methods

• public static void bind(String url, Remote obj) - Binding means associating a name for a remote object that can be used to look up that remote object. This method binds the specified "name" to a remote object. It throws an AlreadyBoundException if the name is already bound to an object.

• public static String[] list(String url) - Returns an array of the Strings bound in the registry. Each String object contains a name that is bound to a remote object. The names are URL-formatted strings.

• public static Remote lookup(String url) - Returns a stub for the remote object associated with the specified name. This method takes a string containing the URL to a remote object reference on the server.

• public static void rebind(String url, Remote obj) - Rebinds the specified name to a new remote object. Any old binding for the name is replaced.

• public static void unbind(String url) - Removes an object reference from the registry. It throws a NotBoundException if there was no binding.

To develop and run a distributed application using RMI we have to follow steps given below:

• Define the interfaces
• Implementing these interfaces
• Compile the application with the java compiler
• Compile the server implementation with the rmic compiler.
• Run the RMI registry
• Run the server
• Run the client