RemoteObject class implements the
* java.lang.Object behavior for remote objects.
* RemoteObject provides the remote semantics of Object by
* implementing methods for hashCode, equals, and toString.
*
* @author Ann Wollrath
* @author Laird Dornin
* @author Peter Jones
* @since JDK1.1
*/
public abstract class RemoteObject implements Remote, java.io.Serializable {
/** The object's remote reference. */
transient protected RemoteRef ref;
/** indicate compatibility with JDK 1.1.x version of class */
private static final long serialVersionUID = -3215090123894869218L;
/**
* Creates a remote object.
*/
protected RemoteObject() {
ref = null;
}
/**
* Creates a remote object, initialized with the specified remote
* reference.
* @param newref remote reference
*/
protected RemoteObject(RemoteRef newref) {
ref = newref;
}
/**
* Returns the remote reference for the remote object.
*
* Note: The object returned from this method may be an instance of
* an implementation-specific class. The RemoteObject
* class ensures serialization portability of its instances' remote
* references through the behavior of its custom
* writeObject and readObject methods. An
* instance of RemoteRef should not be serialized outside
* of its RemoteObject wrapper instance or the result may
* be unportable.
*
* @return remote reference for the remote object
* @since 1.2
*/
public RemoteRef getRef() {
return ref;
}
/**
* Returns the stub for the remote object obj passed
* as a parameter. This operation is only valid after
* the object has been exported.
* @param obj the remote object whose stub is needed
* @return the stub for the remote object, obj.
* @exception NoSuchObjectException if the stub for the
* remote object could not be found.
* @since 1.2
*/
public static Remote toStub(Remote obj) throws NoSuchObjectException {
if (obj instanceof RemoteStub ||
(obj != null &&
Proxy.isProxyClass(obj.getClass()) &&
Proxy.getInvocationHandler(obj) instanceof
RemoteObjectInvocationHandler))
{
return obj;
} else {
return sun.rmi.transport.ObjectTable.getStub(obj);
}
}
/**
* Returns a hashcode for a remote object. Two remote object stubs
* that refer to the same remote object will have the same hash code
* (in order to support remote objects as keys in hash tables).
*
* @see java.util.Hashtable
*/
public int hashCode() {
return (ref == null) ? super.hashCode() : ref.remoteHashCode();
}
/**
* Compares two remote objects for equality.
* Returns a boolean that indicates whether this remote object is
* equivalent to the specified Object. This method is used when a
* remote object is stored in a hashtable.
* If the specified Object is not itself an instance of RemoteObject,
* then this method delegates by returning the result of invoking the
* equals method of its parameter with this remote object
* as the argument.
* @param obj the Object to compare with
* @return true if these Objects are equal; false otherwise.
* @see java.util.Hashtable
*/
public boolean equals(Object obj) {
if (obj instanceof RemoteObject) {
if (ref == null) {
return obj == this;
} else {
return ref.remoteEquals(((RemoteObject)obj).ref);
}
} else if (obj != null) {
/*
* Fix for 4099660: if object is not an instance of RemoteObject,
* use the result of its equals method, to support symmetry is a
* remote object implementation class that does not extend
* RemoteObject wishes to support equality with its stub objects.
*/
return obj.equals(this);
} else {
return false;
}
}
/**
* Returns a String that represents the value of this remote object.
*/
public String toString() {
String classname = Util.getUnqualifiedName(getClass());
return (ref == null) ? classname :
classname + "[" + ref.remoteToString() + "]";
}
/**
* writeObject for custom serialization.
*
*
This method writes this object's serialized form for this class * as follows: * *
The {@link RemoteRef#getRefClass(java.io.ObjectOutput) getRefClass}
* method is invoked on this object's ref field
* to obtain its external ref type name.
* If the value returned by getRefClass was
* a non-null string of length greater than zero,
* the writeUTF method is invoked on out
* with the value returned by getRefClass, and then
* the writeExternal method is invoked on
* this object's ref field passing out
* as the argument; otherwise,
* the writeUTF method is invoked on out
* with a zero-length string (""), and then
* the writeObject method is invoked on out
* passing this object's ref field as the argument.
*
* @serialData
*
* The serialized data for this class comprises a string (written with
* ObjectOutput.writeUTF) that is either the external
* ref type name of the contained RemoteRef instance
* (the ref field) or a zero-length string, followed by
* either the external form of the ref field as written by
* its writeExternal method if the string was of non-zero
* length, or the serialized form of the ref field as
* written by passing it to the serialization stream's
* writeObject if the string was of zero length.
*
*
If this object is an instance of
* {@link RemoteStub} or {@link RemoteObjectInvocationHandler}
* that was returned from any of
* the UnicastRemoteObject.exportObject methods
* and custom socket factories are not used,
* the external ref type name is "UnicastRef".
*
* If this object is an instance of
* RemoteStub or RemoteObjectInvocationHandler
* that was returned from any of
* the UnicastRemoteObject.exportObject methods
* and custom socket factories are used,
* the external ref type name is "UnicastRef2".
*
* If this object is an instance of
* RemoteStub or RemoteObjectInvocationHandler
* that was returned from any of
* the java.rmi.activation.Activatable.exportObject methods,
* the external ref type name is "ActivatableRef".
*
* If this object is an instance of
* RemoteStub or RemoteObjectInvocationHandler
* that was returned from
* the RemoteObject.toStub method (and the argument passed
* to toStub was not itself a RemoteStub),
* the external ref type name is a function of how the remote object
* passed to toStub was exported, as described above.
*
* If this object is an instance of
* RemoteStub or RemoteObjectInvocationHandler
* that was originally created via deserialization,
* the external ref type name is the same as that which was read
* when this object was deserialized.
*
*
If this object is an instance of
* java.rmi.server.UnicastRemoteObject that does not
* use custom socket factories,
* the external ref type name is "UnicastServerRef".
*
* If this object is an instance of
* UnicastRemoteObject that does
* use custom socket factories,
* the external ref type name is "UnicastServerRef2".
*
*
Following is the data that must be written by the
* writeExternal method and read by the
* readExternal method of RemoteRef
* implementation classes that correspond to the each of the
* defined external ref type names:
*
*
For "UnicastRef":
*
*
ObjID instance contained in the reference
*
* false,
* written by {@link java.io.ObjectOutput#writeBoolean(boolean)}
*
* For "UnicastRef2" with a
* null client socket factory:
*
*
0x00
* (indicating null client socket factory),
* written by {@link java.io.ObjectOutput#writeByte(int)}
*
* ObjID instance contained in the reference
*
* false,
* written by {@link java.io.ObjectOutput#writeBoolean(boolean)}
*
* For "UnicastRef2" with a
* non-null client socket factory:
*
*
0x01
* (indicating non-null client socket factory),
* written by {@link java.io.ObjectOutput#writeByte(int)}
*
* java.rmi.server.RMIClientSocketFactory),
* written by passing it to an invocation of
* writeObject on the stream instance
*
* ObjID instance contained in the reference
*
* false,
* written by {@link java.io.ObjectOutput#writeBoolean(boolean)}
*
* For "ActivatableRef" with a
* null nested remote reference:
*
*
java.rmi.activation.ActivationID,
* written by passing it to an invocation of
* writeObject on the stream instance
*
* ""),
* written by {@link java.io.ObjectOutput#writeUTF(String)}
*
* For "ActivatableRef" with a
* non-null nested remote reference:
*
*
java.rmi.activation.ActivationID,
* written by passing it to an invocation of
* writeObject on the stream instance
*
* "UnicastRef2",
* written by {@link java.io.ObjectOutput#writeUTF(String)}
*
* writeExternal method
* with the stream instance
* (see the description of the external form for
* "UnicastRef2" above)
*
* For "UnicastServerRef" and
* "UnicastServerRef2", no data is written by the
* writeExternal method or read by the
* readExternal method.
*/
private void writeObject(java.io.ObjectOutputStream out)
throws java.io.IOException, java.lang.ClassNotFoundException
{
if (ref == null) {
throw new java.rmi.MarshalException("Invalid remote object");
} else {
String refClassName = ref.getRefClass(out);
if (refClassName == null || refClassName.length() == 0) {
/*
* No reference class name specified, so serialize
* remote reference.
*/
out.writeUTF("");
out.writeObject(ref);
} else {
/*
* Built-in reference class specified, so delegate
* to reference to write out its external form.
*/
out.writeUTF(refClassName);
ref.writeExternal(out);
}
}
}
/**
* readObject for custom serialization.
*
*
This method reads this object's serialized form for this class * as follows: * *
The readUTF method is invoked on in
* to read the external ref type name for the RemoteRef
* instance to be filled in to this object's ref field.
* If the string returned by readUTF has length zero,
* the readObject method is invoked on in,
* and than the value returned by readObject is cast to
* RemoteRef and this object's ref field is
* set to that value.
* Otherwise, this object's ref field is set to a
* RemoteRef instance that is created of an
* implementation-specific class corresponding to the external ref
* type name returned by readUTF, and then
* the readExternal method is invoked on
* this object's ref field.
*
*
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 this object's ref field will be set to an
* instance of that implementation-specific class.
*/
private void readObject(java.io.ObjectInputStream in)
throws java.io.IOException, java.lang.ClassNotFoundException
{
String refClassName = in.readUTF();
if (refClassName == null || refClassName.length() == 0) {
/*
* No reference class name specified, so construct
* remote reference from its serialized form.
*/
ref = (RemoteRef) in.readObject();
} else {
/*
* Built-in reference class specified, so delegate to
* internal reference class to initialize its fields from
* its external form.
*/
String internalRefClassName =
RemoteRef.packagePrefix + "." + refClassName;
Class refClass = Class.forName(internalRefClassName);
try {
ref = (RemoteRef) refClass.newInstance();
/*
* If this step fails, assume we found an internal
* class that is not meant to be a serializable ref
* type.
*/
} catch (InstantiationException e) {
throw new ClassNotFoundException(internalRefClassName, e);
} catch (IllegalAccessException e) {
throw new ClassNotFoundException(internalRefClassName, e);
} catch (ClassCastException e) {
throw new ClassNotFoundException(internalRefClassName, e);
}
ref.readExternal(in);
}
}
}