package java.rmi;
public interface Remote {}
java.rmi.Remote
interface serves to identify all remote objects, all
remote objects must directly or indirectly implement this interface. Note that
all remote interfaces must be declared public
.
java.rmi.RemoteException
. This
allows interfaces to handle all types of remote exceptions and to distinguish
local exceptions, and exceptions specific to the method, from exceptions
thrown by the underlying distributed object mechanisms.
package java.rmi;
public class RemoteException extends java.io.IOException
{
// The actual exception or error that occurred.
public Throwable detail;
// Create a remote exception.
public RemoteException();
// Create a remote exception with the specified string.
public RemoteException(String s);
// Create remote exception with specified string and exception.
public RemoteException(String s, Throwable ex);
// Produce message, including message from any nested exception.
public String getMessage();
}
RemoteException
can be constructed with a nested exception (a
Throwable
). Typically, the nested exception, ex, specified as a parameter in
the third form of the constructor, is the underlying I/O exception that occurred
during an RMI call.
java.rmi.Naming
class allows remote objects to be retrieved and defined
using the familiar Uniform Resource Locator (URL) syntax. The URL consists
of protocol, host, port, and name fields. The Registry
service on the specified
host and port is used to perform the specified operation. The protocol should
be specified as rmi
, as in rmi://java.sun.com:2001/root
.
package java.rmi;
public final class Naming {
public static Remote lookup(String url)
throws NotBoundException, java.net.MalformedURLException,
UnknownHostException, RemoteException;
public static void bind(String url, Remote obj)
throws AlreadyBoundException,
java.net.MalformedURLException, UnknownHostException,
RemoteException;
public static void rebind(String url, Remote obj)
throws RemoteException, java.net.MalformedURLException,
UnknownHostException;
public static void unbind(String url)
throws RemoteException, NotBoundException,
java.net.MalformedURLException, UnknownHostException;
public static String[] list(String url)
throws RemoteException, java.net.MalformedURLException,
UnknownHostException;
}
lookup
method returns the remote object associated with the file portion
of the name; so in the preceding example it would return the object named
root
. The NotBoundException
is thrown if the name has not been bound to
an object.
The bind
method binds the specified name to the remote object. It throws the
AlreadyBoundException
if the name is already bound to an object.
The rebind
method always binds the name to the object even if the name is
already bound. The old binding is lost.
The unbind
method removes the binding between the name and the remote
object. It will throw the NotBoundException
if there was no binding.
The list
method returns an array of Strings
containing a snapshot of the
URLs bound in the registry. Only the host and port information of the URL is
needed to contact a registry for the list of its contents; thus, the "file" part of
the URL is ignored.
The java.rmi.AccessException
may also be thrown as a result of
any of these methods. The AccessException
indicates that the caller does
not have permission to execute the specific operation. For example, only
clients that are local to the host on which the registry runs are permitted to
execute the operations, bind
, rebind
, and unbind
. A lookup
operation,
however can be invoked from any non-local client.