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package java.rmi.activation;
import java.io.IOException;
import java.io.InvalidObjectException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Proxy;
import java.rmi.MarshalledObject;
import java.rmi.Remote;
import java.rmi.RemoteException;
import java.rmi.UnmarshalException;
import java.rmi.server.RemoteObject;
import java.rmi.server.RemoteObjectInvocationHandler;
import java.rmi.server.RemoteRef;
import java.rmi.server.UID;
import java.security.AccessControlContext;
import java.security.AccessController;
import java.security.Permissions;
import java.security.PrivilegedActionException;
import java.security.PrivilegedExceptionAction;
import java.security.ProtectionDomain;
Activation makes use of special identifiers to denote remote
objects that can be activated over time. An activation identifier
(an instance of the class ActivationID) contains several
pieces of information needed for activating an object:
- a remote reference to the object's activator (a
RemoteRef instance), and - a unique identifier (a
UID instance) for the object.
An activation identifier for an object can be obtained by registering
an object with the activation system. Registration is accomplished
in a few ways:
- via the
Activatable.register method
- via the first
Activatable constructor (that takes
three arguments and both registers and exports the object, and
- via the first
Activatable.exportObject method
that takes the activation descriptor, object and port as arguments;
this method both registers and exports the object.
Author: Ann Wollrath See Also: Since: 1.2
/**
* Activation makes use of special identifiers to denote remote
* objects that can be activated over time. An activation identifier
* (an instance of the class <code>ActivationID</code>) contains several
* pieces of information needed for activating an object:
* <ul>
* <li> a remote reference to the object's activator (a {@link
* java.rmi.server.RemoteRef RemoteRef}
* instance), and
* <li> a unique identifier (a {@link java.rmi.server.UID UID}
* instance) for the object. </ul> <p>
*
* An activation identifier for an object can be obtained by registering
* an object with the activation system. Registration is accomplished
* in a few ways: <ul>
* <li>via the <code>Activatable.register</code> method
* <li>via the first <code>Activatable</code> constructor (that takes
* three arguments and both registers and exports the object, and
* <li>via the first <code>Activatable.exportObject</code> method
* that takes the activation descriptor, object and port as arguments;
* this method both registers and exports the object. </ul>
*
* @author Ann Wollrath
* @see Activatable
* @since 1.2
*/
public class ActivationID implements Serializable {
the object's activator
/**
* the object's activator
*/
private transient Activator activator;
the object's unique id
/**
* the object's unique id
*/
private transient UID uid = new UID();
indicate compatibility with the Java 2 SDK v1.2 version of class /** indicate compatibility with the Java 2 SDK v1.2 version of class */
private static final long serialVersionUID = -4608673054848209235L;
an AccessControlContext with no permissions /** an AccessControlContext with no permissions */
private static final AccessControlContext NOPERMS_ACC;
static {
Permissions perms = new Permissions();
ProtectionDomain[] pd = { new ProtectionDomain(null, perms) };
NOPERMS_ACC = new AccessControlContext(pd);
}
The constructor for ActivationID takes a single
argument, activator, that specifies a remote reference to the
activator responsible for activating the object associated with
this identifier. An instance of ActivationID is globally
unique.
Params: - activator – reference to the activator responsible for
activating the object
Throws: - UnsupportedOperationException – if and only if activation is
not supported by this implementation
Since: 1.2
/**
* The constructor for <code>ActivationID</code> takes a single
* argument, activator, that specifies a remote reference to the
* activator responsible for activating the object associated with
* this identifier. An instance of <code>ActivationID</code> is globally
* unique.
*
* @param activator reference to the activator responsible for
* activating the object
* @throws UnsupportedOperationException if and only if activation is
* not supported by this implementation
* @since 1.2
*/
public ActivationID(Activator activator) {
this.activator = activator;
}
Activate the object for this id.
Params: - force – if true, forces the activator to contact the group
when activating the object (instead of returning a cached reference);
if false, returning a cached value is acceptable.
Throws: - ActivationException – if activation fails
- UnknownObjectException – if the object is unknown
- RemoteException – if remote call fails
Returns: the reference to the active remote object Since: 1.2
/**
* Activate the object for this id.
*
* @param force if true, forces the activator to contact the group
* when activating the object (instead of returning a cached reference);
* if false, returning a cached value is acceptable.
* @return the reference to the active remote object
* @exception ActivationException if activation fails
* @exception UnknownObjectException if the object is unknown
* @exception RemoteException if remote call fails
* @since 1.2
*/
public Remote activate(boolean force)
throws ActivationException, UnknownObjectException, RemoteException
{
try {
MarshalledObject<? extends Remote> mobj =
activator.activate(this, force);
return AccessController.doPrivileged(
new PrivilegedExceptionAction<Remote>() {
public Remote run() throws IOException, ClassNotFoundException {
return mobj.get();
}
}, NOPERMS_ACC);
} catch (PrivilegedActionException pae) {
Exception ex = pae.getException();
if (ex instanceof RemoteException) {
throw (RemoteException) ex;
} else {
throw new UnmarshalException("activation failed", ex);
}
}
}
Returns a hashcode for the activation id. Two identifiers that
refer to the same remote object will have the same hash code.
See Also: - Hashtable
Since: 1.2
/**
* Returns a hashcode for the activation id. Two identifiers that
* refer to the same remote object will have the same hash code.
*
* @see java.util.Hashtable
* @since 1.2
*/
public int hashCode() {
return uid.hashCode();
}
Compares two activation ids for content equality.
Returns true if both of the following conditions are true:
1) the unique identifiers equivalent (by content), and
2) the activator specified in each identifier
refers to the same remote object.
Params: - obj – the Object to compare with
See Also: Returns: true if these Objects are equal; false otherwise. Since: 1.2
/**
* Compares two activation ids for content equality.
* Returns true if both of the following conditions are true:
* 1) the unique identifiers equivalent (by content), and
* 2) the activator specified in each identifier
* refers to the same remote object.
*
* @param obj the Object to compare with
* @return true if these Objects are equal; false otherwise.
* @see java.util.Hashtable
* @since 1.2
*/
public boolean equals(Object obj) {
if (obj instanceof ActivationID) {
ActivationID id = (ActivationID) obj;
return (uid.equals(id.uid) && activator.equals(id.activator));
} else {
return false;
}
}
writeObject for custom serialization.
This method writes this object's serialized form for
this class as follows:
The writeObject method is invoked on
out passing this object's unique identifier (a UID instance) as the argument.
Next, the
getRefClass method is invoked on the activator's RemoteRef instance to obtain its external ref
type name. Next, the writeUTF method is
invoked on out with the value returned by
getRefClass, and then the
writeExternal method is invoked on the
RemoteRef instance passing out
as the argument.
@serialData The serialized data for this class comprises a
java.rmi.server.UID (written with
ObjectOutput.writeObject) followed by the
external ref type name of the activator's
RemoteRef instance (a string written with
ObjectOutput.writeUTF), followed by the
external form of the RemoteRef instance as
written by its writeExternal method.
The external ref type name of the
RemoteRef instance is determined using the definitions of external ref type names specified in the
RemoteObject writeObject method
serialData specification. Similarly, the data
written by the writeExternal method and read
by the readExternal method of
RemoteRef implementation classes corresponding to each of the defined external ref type names is specified in the RemoteObject writeObject method serialData
specification.
/**
* <code>writeObject</code> for custom serialization.
*
* <p>This method writes this object's serialized form for
* this class as follows:
*
* <p>The <code>writeObject</code> method is invoked on
* <code>out</code> passing this object's unique identifier
* (a {@link java.rmi.server.UID UID} instance) as the argument.
*
* <p>Next, the {@link
* java.rmi.server.RemoteRef#getRefClass(java.io.ObjectOutput)
* getRefClass} method is invoked on the activator's
* <code>RemoteRef</code> instance to obtain its external ref
* type name. Next, the <code>writeUTF</code> method is
* invoked on <code>out</code> with the value returned by
* <code>getRefClass</code>, and then the
* <code>writeExternal</code> method is invoked on the
* <code>RemoteRef</code> instance passing <code>out</code>
* as the argument.
*
* @serialData The serialized data for this class comprises a
* <code>java.rmi.server.UID</code> (written with
* <code>ObjectOutput.writeObject</code>) followed by the
* external ref type name of the activator's
* <code>RemoteRef</code> instance (a string written with
* <code>ObjectOutput.writeUTF</code>), followed by the
* external form of the <code>RemoteRef</code> instance as
* written by its <code>writeExternal</code> method.
*
* <p>The external ref type name of the
* <code>RemoteRef</Code> instance is
* determined using the definitions of external ref type
* names specified in the {@link java.rmi.server.RemoteObject
* RemoteObject} <code>writeObject</code> method
* <b>serialData</b> specification. Similarly, the data
* written by the <code>writeExternal</code> method and read
* by the <code>readExternal</code> method of
* <code>RemoteRef</code> implementation classes
* corresponding to each of the defined external ref type
* names is specified in the {@link
* java.rmi.server.RemoteObject RemoteObject}
* <code>writeObject</code> method <b>serialData</b>
* specification.
**/
private void writeObject(ObjectOutputStream out)
throws IOException, ClassNotFoundException
{
out.writeObject(uid);
RemoteRef ref;
if (activator instanceof RemoteObject) {
ref = ((RemoteObject) activator).getRef();
} else if (Proxy.isProxyClass(activator.getClass())) {
InvocationHandler handler = Proxy.getInvocationHandler(activator);
if (!(handler instanceof RemoteObjectInvocationHandler)) {
throw new InvalidObjectException(
"unexpected invocation handler");
}
ref = ((RemoteObjectInvocationHandler) handler).getRef();
} else {
throw new InvalidObjectException("unexpected activator type");
}
out.writeUTF(ref.getRefClass(out));
ref.writeExternal(out);
}
readObject for custom serialization.
This method reads this object's serialized form for this
class as follows:
The readObject method is invoked on
in to read this object's unique identifier (a UID instance).
Next, the readUTF method is invoked on
in to read the external ref type name of the
RemoteRef instance for this object's
activator. Next, the RemoteRef
instance is created of an implementation-specific class
corresponding to the external ref type name (returned by
readUTF), and the readExternal
method is invoked on that RemoteRef instance
to read the external form corresponding to the external
ref type name.
Note: If the external ref type name is
"UnicastRef", "UnicastServerRef",
"UnicastRef2", "UnicastServerRef2",
or "ActivatableRef", a corresponding
implementation-specific class must be found, and its
readExternal method must read the serial data
for that external ref type name as specified to be written
in the serialData documentation for this class.
If the external ref type name is any other string (of non-zero
length), a ClassNotFoundException will be thrown,
unless the implementation provides an implementation-specific
class corresponding to that external ref type name, in which
case the RemoteRef will be an instance of
that implementation-specific class.
/**
* <code>readObject</code> for custom serialization.
*
* <p>This method reads this object's serialized form for this
* class as follows:
*
* <p>The <code>readObject</code> method is invoked on
* <code>in</code> to read this object's unique identifier
* (a {@link java.rmi.server.UID UID} instance).
*
* <p>Next, the <code>readUTF</code> method is invoked on
* <code>in</code> to read the external ref type name of the
* <code>RemoteRef</code> instance for this object's
* activator. Next, the <code>RemoteRef</code>
* instance is created of an implementation-specific class
* corresponding to the external ref type name (returned by
* <code>readUTF</code>), and the <code>readExternal</code>
* method is invoked on that <code>RemoteRef</code> instance
* to read the external form corresponding to the external
* ref type name.
*
* <p>Note: If the external ref type name is
* <code>"UnicastRef"</code>, <code>"UnicastServerRef"</code>,
* <code>"UnicastRef2"</code>, <code>"UnicastServerRef2"</code>,
* or <code>"ActivatableRef"</code>, a corresponding
* implementation-specific class must be found, and its
* <code>readExternal</code> method must read the serial data
* for that external ref type name as specified to be written
* in the <b>serialData</b> documentation for this class.
* If the external ref type name is any other string (of non-zero
* length), a <code>ClassNotFoundException</code> will be thrown,
* unless the implementation provides an implementation-specific
* class corresponding to that external ref type name, in which
* case the <code>RemoteRef</code> will be an instance of
* that implementation-specific class.
*/
private void readObject(ObjectInputStream in)
throws IOException, ClassNotFoundException
{
uid = (UID)in.readObject();
try {
Class<? extends RemoteRef> refClass =
Class.forName(RemoteRef.packagePrefix + "." + in.readUTF())
.asSubclass(RemoteRef.class);
RemoteRef ref = refClass.newInstance();
ref.readExternal(in);
activator = (Activator)
Proxy.newProxyInstance(null,
new Class<?>[] { Activator.class },
new RemoteObjectInvocationHandler(ref));
} catch (InstantiationException e) {
throw (IOException)
new InvalidObjectException(
"Unable to create remote reference").initCause(e);
} catch (IllegalAccessException e) {
throw (IOException)
new InvalidObjectException(
"Unable to create remote reference").initCause(e);
}
}
}