Class ActivationGroup
- java.lang.Object
-
- java.rmi.server.RemoteObject
-
- java.rmi.server.RemoteServer
-
- java.rmi.server.UnicastRemoteObject
-
- java.rmi.activation.ActivationGroup
- All Implemented Interfaces:
-
Serializable
,ActivationInstantiator
,Remote
public abstract class ActivationGroup extends UnicastRemoteObject implements ActivationInstantiator
An ActivationGroup
is responsible for creating new instances of "activatable" objects in its group, informing its ActivationMonitor
when either: its object's become active or inactive, or the group as a whole becomes inactive.
An ActivationGroup
is initially created in one of several ways:
- as a side-effect of creating an
ActivationDesc
without an explicitActivationGroupID
for the first activatable object in the group, or - via the
ActivationGroup.createGroup
method - as a side-effect of activating the first object in a group whose
ActivationGroupDesc
was only registered.
Only the activator can recreate an ActivationGroup
. The activator spawns, as needed, a separate VM (as a child process, for example) for each registered activation group and directs activation requests to the appropriate group. It is implementation specific how VMs are spawned. An activation group is created via the ActivationGroup.createGroup
static method. The createGroup
method has two requirements on the group to be created: 1) the group must be a concrete subclass of ActivationGroup
, and 2) the group must have a constructor that takes two arguments:
- the group's
ActivationGroupID
, and - the group's initialization data (in a
java.rmi.MarshalledObject
)
When created, the default implementation of ActivationGroup
will override the system properties with the properties requested when its ActivationGroupDesc
was created, and will set a SecurityManager
as the default system security manager. If your application requires specific properties to be set when objects are activated in the group, the application should create a special Properties
object containing these properties, then create an ActivationGroupDesc
with the Properties
object, and use ActivationGroup.createGroup
before creating any ActivationDesc
s (before the default ActivationGroupDesc
is created). If your application requires the use of a security manager other than SecurityManager
, in the ActivativationGroupDescriptor properties list you can set java.security.manager
property to the name of the security manager you would like to install.
- Since:
- 1.2
- See Also:
-
ActivationInstantiator
,ActivationGroupDesc
,ActivationGroupID
, Serialized Form
Field Summary
Fields declared in class java.rmi.server.RemoteObject
ref
Constructor Summary
Modifier | Constructor | Description |
---|---|---|
protected | ActivationGroup(ActivationGroupID groupID) | Constructs an activation group with the given activation group identifier. |
Method Summary
Modifier and Type | Method | Description |
---|---|---|
protected void | activeObject(ActivationID id,
MarshalledObject<? extends Remote> mobj) | This protected method is necessary for subclasses to make the |
abstract void | activeObject(ActivationID id,
Remote obj) | The group's |
static ActivationGroup | createGroup(ActivationGroupID id,
ActivationGroupDesc desc,
long incarnation) | Create and set the activation group for the current VM. |
static ActivationGroupID | currentGroupID() | Returns the current activation group's identifier. |
static ActivationSystem | getSystem() | Returns the activation system for the VM. |
protected void | inactiveGroup() | This protected method is necessary for subclasses to make the |
boolean | inactiveObject(ActivationID id) | The group's |
static void | setSystem(ActivationSystem system) | Set the activation system for the VM. |
Methods declared in class java.rmi.server.UnicastRemoteObject
clone, exportObject, exportObject, exportObject, exportObject, exportObject, unexportObject
Methods declared in class java.rmi.server.RemoteServer
getClientHost, getLog, setLog
Methods declared in class java.rmi.server.RemoteObject
equals, getRef, hashCode, toString, toStub
Methods declared in class java.lang.Object
finalize, getClass, notify, notifyAll, wait, wait, wait
Methods declared in interface java.rmi.activation.ActivationInstantiator
newInstance
Constructor Detail
ActivationGroup
protected ActivationGroup(ActivationGroupID groupID) throws RemoteException
Constructs an activation group with the given activation group identifier. The group is exported as a java.rmi.server.UnicastRemoteObject
.
- Parameters:
-
groupID
- the group's identifier - Throws:
-
RemoteException
- if this group could not be exported -
UnsupportedOperationException
- if and only if activation is not supported by this implementation - Since:
- 1.2
Method Detail
inactiveObject
public boolean inactiveObject(ActivationID id) throws ActivationException, UnknownObjectException, RemoteException
The group's inactiveObject
method is called indirectly via a call to the Activatable.inactive
method. A remote object implementation must call Activatable
's inactive
method when that object deactivates (the object deems that it is no longer active). If the object does not call Activatable.inactive
when it deactivates, the object will never be garbage collected since the group keeps strong references to the objects it creates.
The group's inactiveObject
method unexports the remote object from the RMI runtime so that the object can no longer receive incoming RMI calls. An object will only be unexported if the object has no pending or executing calls. The subclass of ActivationGroup
must override this method and unexport the object.
After removing the object from the RMI runtime, the group must inform its ActivationMonitor
(via the monitor's inactiveObject
method) that the remote object is not currently active so that the remote object will be re-activated by the activator upon a subsequent activation request.
This method simply informs the group's monitor that the object is inactive. It is up to the concrete subclass of ActivationGroup to fulfill the additional requirement of unexporting the object.
- Parameters:
-
id
- the object's activation identifier - Returns:
- true if the object was successfully deactivated; otherwise returns false.
- Throws:
-
UnknownObjectException
- if object is unknown (may already be inactive) -
RemoteException
- if call informing monitor fails -
ActivationException
- if group is inactive - Since:
- 1.2
activeObject
public abstract void activeObject(ActivationID id, Remote obj) throws ActivationException, UnknownObjectException, RemoteException
The group's activeObject
method is called when an object is exported (either by Activatable
object construction or an explicit call to Activatable.exportObject
. The group must inform its ActivationMonitor
that the object is active (via the monitor's activeObject
method) if the group hasn't already done so.
- Parameters:
-
id
- the object's identifier -
obj
- the remote object implementation - Throws:
-
UnknownObjectException
- if object is not registered -
RemoteException
- if call informing monitor fails -
ActivationException
- if group is inactive - Since:
- 1.2
createGroup
public static ActivationGroup createGroup(ActivationGroupID id, ActivationGroupDesc desc, long incarnation) throws ActivationException
Create and set the activation group for the current VM. The activation group can only be set if it is not currently set. An activation group is set using the createGroup
method when the Activator
initiates the re-creation of an activation group in order to carry out incoming activate
requests. A group must first be registered with the ActivationSystem
before it can be created via this method.
The group class specified by the ActivationGroupDesc
must be a concrete subclass of ActivationGroup
and have a public constructor that takes two arguments: the ActivationGroupID
for the group and the MarshalledObject
containing the group's initialization data (obtained from the ActivationGroupDesc
.
If the group class name specified in the ActivationGroupDesc
is null
, then this method will behave as if the group descriptor contained the name of the default activation group implementation class.
Note that if your application creates its own custom activation group, a security manager must be set for that group. Otherwise objects cannot be activated in the group. SecurityManager
is set by default.
If a security manager is already set in the group VM, this method first calls the security manager's checkSetFactory
method. This could result in a SecurityException
. If your application needs to set a different security manager, you must ensure that the policy file specified by the group's ActivationGroupDesc
grants the group the necessary permissions to set a new security manager. (Note: This will be necessary if your group downloads and sets a security manager).
After the group is created, the ActivationSystem
is informed that the group is active by calling the activeGroup
method which returns the ActivationMonitor
for the group. The application need not call activeGroup
independently since it is taken care of by this method.
Once a group is created, subsequent calls to the currentGroupID
method will return the identifier for this group until the group becomes inactive.
- Parameters:
-
id
- the activation group's identifier -
desc
- the activation group's descriptor -
incarnation
- the group's incarnation number (zero on group's initial creation) - Returns:
- the activation group for the VM
- Throws:
-
ActivationException
- if group already exists or if error occurs during group creation -
SecurityException
- if permission to create group is denied. (Note: The default implementation of the security managercheckSetFactory
method requires the RuntimePermission "setFactory") -
UnsupportedOperationException
- if and only if activation is not supported by this implementation - Since:
- 1.2
- See Also:
SecurityManager.checkSetFactory()
currentGroupID
public static ActivationGroupID currentGroupID()
Returns the current activation group's identifier. Returns null if no group is currently active for this VM.
- Returns:
- the activation group's identifier
- Throws:
-
UnsupportedOperationException
- if and only if activation is not supported by this implementation - Since:
- 1.2
setSystem
public static void setSystem(ActivationSystem system) throws ActivationException
Set the activation system for the VM. The activation system can only be set it if no group is currently active. If the activation system is not set via this call, then the getSystem
method attempts to obtain a reference to the ActivationSystem
by looking up the name "java.rmi.activation.ActivationSystem" in the Activator's registry. By default, the port number used to look up the activation system is defined by ActivationSystem.SYSTEM_PORT
. This port can be overridden by setting the property java.rmi.activation.port
.
If there is a security manager, this method first calls the security manager's checkSetFactory
method. This could result in a SecurityException.
- Parameters:
-
system
- remote reference to theActivationSystem
- Throws:
-
ActivationException
- if activation system is already set -
SecurityException
- if permission to set the activation system is denied. (Note: The default implementation of the security managercheckSetFactory
method requires the RuntimePermission "setFactory") -
UnsupportedOperationException
- if and only if activation is not supported by this implementation - Since:
- 1.2
- See Also:
-
getSystem()
,SecurityManager.checkSetFactory()
getSystem
public static ActivationSystem getSystem() throws ActivationException
Returns the activation system for the VM. The activation system may be set by the setSystem
method. If the activation system is not set via the setSystem
method, then the getSystem
method attempts to obtain a reference to the ActivationSystem
by looking up the name "java.rmi.activation.ActivationSystem" in the Activator's registry. By default, the port number used to look up the activation system is defined by ActivationSystem.SYSTEM_PORT
. This port can be overridden by setting the property java.rmi.activation.port
.
- Returns:
- the activation system for the VM/group
- Throws:
-
ActivationException
- if activation system cannot be obtained or is not bound (means that it is not running) -
UnsupportedOperationException
- if and only if activation is not supported by this implementation - Since:
- 1.2
- See Also:
setSystem(java.rmi.activation.ActivationSystem)
activeObject
protected void activeObject(ActivationID id, MarshalledObject<? extends Remote> mobj) throws ActivationException, UnknownObjectException, RemoteException
This protected method is necessary for subclasses to make the activeObject
callback to the group's monitor. The call is simply forwarded to the group's ActivationMonitor
.
- Parameters:
-
id
- the object's identifier -
mobj
- a marshalled object containing the remote object's stub - Throws:
-
UnknownObjectException
- if object is not registered -
RemoteException
- if call informing monitor fails -
ActivationException
- if an activation error occurs - Since:
- 1.2
inactiveGroup
protected void inactiveGroup() throws UnknownGroupException, RemoteException
This protected method is necessary for subclasses to make the inactiveGroup
callback to the group's monitor. The call is simply forwarded to the group's ActivationMonitor
. Also, the current group for the VM is set to null.
- Throws:
-
UnknownGroupException
- if group is not registered -
RemoteException
- if call informing monitor fails - Since:
- 1.2