1 /*
2 * Copyright (c) 1997, 2005, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.rmi.activation;
27
28 import java.rmi.MarshalledObject;
29 import java.rmi.Remote;
30 import java.rmi.RemoteException;
31 import java.rmi.activation.UnknownObjectException;
32
33 /**
34 * The <code>Activator</code> facilitates remote object activation. A
35 * "faulting" remote reference calls the activator's
36 * <code>activate</code> method to obtain a "live" reference to a
37 * "activatable" remote object. Upon receiving a request for activation,
38 * the activator looks up the activation descriptor for the activation
39 * identifier, <code>id</code>, determines the group in which the
40 * object should be activated initiates object re-creation via the
41 * group's <code>ActivationInstantiator</code> (via a call to the
42 * <code>newInstance</code> method). The activator initiates the
43 * execution of activation groups as necessary. For example, if an
44 * activation group for a specific group identifier is not already
45 * executing, the activator initiates the execution of a VM for the
46 * group. <p>
47 *
48 * The <code>Activator</code> works closely with
49 * <code>ActivationSystem</code>, which provides a means for registering
50 * groups and objects within those groups, and <code>ActivationMonitor</code>,
51 * which recives information about active and inactive objects and inactive
52 * groups. <p>
53 *
54 * The activator is responsible for monitoring and detecting when
55 * activation groups fail so that it can remove stale remote references
56 * to groups and active object's within those groups.<p>
57 *
58 * @author Ann Wollrath
59 * @see ActivationInstantiator
60 * @see ActivationGroupDesc
61 * @see ActivationGroupID
62 * @since 1.2
63 */
64 public interface Activator extends Remote {
65 /**
66 * Activate the object associated with the activation identifier,
67 * <code>id</code>. If the activator knows the object to be active
68 * already, and <code>force</code> is false , the stub with a
69 * "live" reference is returned immediately to the caller;
70 * otherwise, if the activator does not know that corresponding
71 * the remote object is active, the activator uses the activation
72 * descriptor information (previously registered) to determine the
73 * group (VM) in which the object should be activated. If an
74 * <code>ActivationInstantiator</code> corresponding to the
75 * object's group descriptor already exists, the activator invokes
76 * the activation group's <code>newInstance</code> method passing
77 * it the object's id and descriptor. <p>
78 *
79 * If the activation group for the object's group descriptor does
80 * not yet exist, the activator starts an
81 * <code>ActivationInstantiator</code> executing (by spawning a
82 * child process, for example). When the activator receives the
83 * activation group's call back (via the
84 * <code>ActivationSystem</code>'s <code>activeGroup</code>
85 * method) specifying the activation group's reference, the
86 * activator can then invoke that activation instantiator's
87 * <code>newInstance</code> method to forward each pending
88 * activation request to the activation group and return the
89 * result (a marshalled remote object reference, a stub) to the
90 * caller.<p>
91 *
92 * Note that the activator receives a "marshalled" object instead of a
93 * Remote object so that the activator does not need to load the
94 * code for that object, or participate in distributed garbage
95 * collection for that object. If the activator kept a strong
96 * reference to the remote object, the activator would then
97 * prevent the object from being garbage collected under the
98 * normal distributed garbage collection mechanism. <p>
99 *
100 * @param id the activation identifier for the object being activated
101 * @param force if true, the activator contacts the group to obtain
102 * the remote object's reference; if false, returning the cached value
103 * is allowed.
104 * @return the remote object (a stub) in a marshalled form
105 * @exception ActivationException if object activation fails
106 * @exception UnknownObjectException if object is unknown (not registered)
107 * @exception RemoteException if remote call fails
108 * @since 1.2
109 */
110 public MarshalledObject<? extends Remote> activate(ActivationID id,
111 boolean force)
112 throws ActivationException, UnknownObjectException, RemoteException;
113
114 }