ActivationGroup (Java Platform SE 8 )
Keywords: java.rmi.activation.ActivationGroup class
Date: 2015-07-19

compact2, compact3
java.rmi.activation

## 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 explicit `ActivationGroupID` 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 inherited from class java.rmi.server.RemoteObject

      `ref`

  - ### Constructor Summary

    Constructors
    Modifier | Constructor and Description
    --- | ---
    `protected` | `ActivationGroup(ActivationGroupID groupID)` Constructs an activation group with the given activation group identifier.

  - ### Method Summary

    All Methods Static Methods Instance Methods Abstract Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `protected void` | `activeObject(ActivationID id, MarshalledObject<? extends Remote> mobj)` This protected method is necessary for subclasses to make the `activeObject` callback to the group's monitor.
    `abstract void` | `activeObject(ActivationID id, Remote obj)` The group's `activeObject` method is called when an object is exported (either by `Activatable` object construction or an explicit call to `Activatable.exportObject`.
    `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 `inactiveGroup` callback to the group's monitor.
    `boolean` | `inactiveObject(ActivationID id)` The group's `inactiveObject` method is called indirectly via a call to the `Activatable.inactive` method.
    `static void` | `setSystem(ActivationSystem system)` Set the activation system for the VM.

    - ### Methods inherited from class java.rmi.server.UnicastRemoteObject

      `clone, exportObject, exportObject, exportObject, unexportObject`

    - ### Methods inherited from class java.rmi.server.RemoteServer

      `getClientHost, getLog, setLog`

    - ### Methods inherited from class java.rmi.server.RemoteObject

      `equals, getRef, hashCode, toString, toStub`

    - ### Methods inherited from class java.lang.Object

      `finalize, getClass, notify, notifyAll, wait, wait, wait`

    - ### Methods inherited from 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 manager `checkSetFactory` 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 the `ActivationSystem`
      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 manager `checkSetFactory` 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

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