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package java.rmi.activation;

import java.rmi.MarshalledObject;
import java.rmi.Remote;
import java.rmi.RemoteException;
import java.rmi.activation.UnknownObjectException;


The Activator facilitates remote object activation. A
"faulting" remote reference calls the activator's
activate method to obtain a "live" reference to a
"activatable" remote object. Upon receiving a request for activation,
the activator looks up the activation descriptor for the activation
identifier, id, determines the group in which the
object should be activated initiates object re-creation via the
group's ActivationInstantiator (via a call to the
newInstance method). The activator initiates the
execution of activation groups as necessary. For example, if an
activation group for a specific group identifier is not already
executing, the activator initiates the execution of a VM for the
group. 

The Activator works closely with
ActivationSystem, which provides a means for registering
groups and objects within those groups, and ActivationMonitor,
which receives information about active and inactive objects and inactive
groups. 

The activator is responsible for monitoring and detecting when
activation groups fail so that it can remove stale remote references
to groups and active object's within those groups.

Author:     Ann Wollrath
See Also:
Since:      1.2
/**
 * The <code>Activator</code> facilitates remote object activation. A
 * "faulting" remote reference calls the activator's
 * <code>activate</code> method to obtain a "live" reference to a
 * "activatable" remote object. Upon receiving a request for activation,
 * the activator looks up the activation descriptor for the activation
 * identifier, <code>id</code>, determines the group in which the
 * object should be activated initiates object re-creation via the
 * group's <code>ActivationInstantiator</code> (via a call to the
 * <code>newInstance</code> method). The activator initiates the
 * execution of activation groups as necessary. For example, if an
 * activation group for a specific group identifier is not already
 * executing, the activator initiates the execution of a VM for the
 * group. <p>
 *
 * The <code>Activator</code> works closely with
 * <code>ActivationSystem</code>, which provides a means for registering
 * groups and objects within those groups, and <code>ActivationMonitor</code>,
 * which receives information about active and inactive objects and inactive
 * groups. <p>
 *
 * The activator is responsible for monitoring and detecting when
 * activation groups fail so that it can remove stale remote references
 * to groups and active object's within those groups.
 *
 * @author      Ann Wollrath
 * @see         ActivationInstantiator
 * @see         ActivationGroupDesc
 * @see         ActivationGroupID
 * @since       1.2
 */
public interface Activator extends Remote {
    
Activate the object associated with the activation identifier,
id. If the activator knows the object to be active
already, and force is false , the stub with a
"live" reference is returned immediately to the caller;
otherwise, if the activator does not know that corresponding
the remote object is active, the activator uses the activation
descriptor information (previously registered) to determine the
group (VM) in which the object should be activated. If an
ActivationInstantiator corresponding to the
object's group descriptor already exists, the activator invokes
the activation group's newInstance method passing
it the object's id and descriptor. 

If the activation group for the object's group descriptor does
not yet exist, the activator starts an
ActivationInstantiator executing (by spawning a
child process, for example). When the activator receives the
activation group's call back (via the
ActivationSystem's activeGroup
method) specifying the activation group's reference, the
activator can then invoke that activation instantiator's
newInstance method to forward each pending
activation request to the activation group and return the
result (a marshalled remote object reference, a stub) to the
caller.

Note that the activator receives a "marshalled" object instead of a
Remote object so that the activator does not need to load the
code for that object, or participate in distributed garbage
collection for that object. If the activator kept a strong
reference to the remote object, the activator would then
prevent the object from being garbage collected under the
normal distributed garbage collection mechanism.

Params:
  • id – the activation identifier for the object being activated
  • force – if true, the activator contacts the group to obtain
the remote object's reference; if false, returning the cached value
is allowed.
Throws:
Returns:the remote object (a stub) in a marshalled form
Since:1.2
/**
     * Activate the object associated with the activation identifier,
     * <code>id</code>. If the activator knows the object to be active
     * already, and <code>force</code> is false , the stub with a
     * "live" reference is returned immediately to the caller;
     * otherwise, if the activator does not know that corresponding
     * the remote object is active, the activator uses the activation
     * descriptor information (previously registered) to determine the
     * group (VM) in which the object should be activated. If an
     * <code>ActivationInstantiator</code> corresponding to the
     * object's group descriptor already exists, the activator invokes
     * the activation group's <code>newInstance</code> method passing
     * it the object's id and descriptor. <p>
     *
     * If the activation group for the object's group descriptor does
     * not yet exist, the activator starts an
     * <code>ActivationInstantiator</code> executing (by spawning a
     * child process, for example). When the activator receives the
     * activation group's call back (via the
     * <code>ActivationSystem</code>'s <code>activeGroup</code>
     * method) specifying the activation group's reference, the
     * activator can then invoke that activation instantiator's
     * <code>newInstance</code> method to forward each pending
     * activation request to the activation group and return the
     * result (a marshalled remote object reference, a stub) to the
     * caller.<p>
     *
     * Note that the activator receives a "marshalled" object instead of a
     * Remote object so that the activator does not need to load the
     * code for that object, or participate in distributed garbage
     * collection for that object. If the activator kept a strong
     * reference to the remote object, the activator would then
     * prevent the object from being garbage collected under the
     * normal distributed garbage collection mechanism.
     *
     * @param id the activation identifier for the object being activated
     * @param force if true, the activator contacts the group to obtain
     * the remote object's reference; if false, returning the cached value
     * is allowed.
     * @return the remote object (a stub) in a marshalled form
     * @exception ActivationException if object activation fails
     * @exception UnknownObjectException if object is unknown (not registered)
     * @exception RemoteException if remote call fails
     * @since 1.2
     */
    public MarshalledObject<? extends Remote> activate(ActivationID id,
                                                       boolean force)
        throws ActivationException, UnknownObjectException, RemoteException;

}