Package gnu.cajo.utils.extra
Class ClientProxy
java.lang.Object
gnu.cajo.utils.extra.ClientProxy
- All Implemented Interfaces:
Invoke
,Serializable
,Remote
This class is used to send server item callbacks to a firewalled client.
A client whose firewall settings prohibit incoming socket connections is a
common problem. This class is called ClientProxy, as it is a stand-in
representation of a remote reference to a client, behind a firewall. This
allows server objects to be designed without regard to client firewall
issues. An intermediary process would give the server item a real remote
reference to the client object when there is no client firewall, or a
ClientProxy when there is. The client links the remote reference to this
ClientProxy, to the locally firewalled client, using an
ItemProxy
object. The server item invokes methods on this client proxy
which result in an immediate callback invocation on the client. Note: this paradigm is not threadsafe! It is expected that callbacks to the remote client will not be invoked reentrantly. Correspondingly, a unique instance of this object must be given to each remote client object. A practical usage example is available online.
- Version:
- 1.0, 28-Mar-04 Initial release
- See Also:
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Field Summary
Fields -
Constructor Summary
ConstructorsConstructorDescriptionA server creates this object, then provides the remote reference member remoteThis to the client. -
Method Summary
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Field Details
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method
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args
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done
private boolean done -
connected
private boolean connected -
timeout
public int timeoutThis is the longest value, in milliseconds, that the server will wait for a client invocation to execute before it aborts it. It is set by default to 5000 (5 seconds). Depending on the type of functionality being performed in the client methods, this time may require adjusting. When it is changed, the new value will apply for all subsequent calls. -
remoteThis
This is the remoted reference to the server's ClientProxy. It is passed back to the client, to be used int theItemProxy
constructor, to create a firewall traversing asynchronous callback link. In order to work, logically, it can only be passed to one remote client.
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Constructor Details
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ClientProxy
A server creates this object, then provides the remote reference member remoteThis to the client. This creates the first half of the bridge, theItemProxy
class completes the second half.- Throws:
RemoteException
- If the remote reference creation fails.
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Method Details
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cutOff
This method abruptly terminates the ClientProxy link to the server. The client can detect the detachment, if it wishes, by implementing a similar cutOff method. The client may also remotely invoke this method, if it wishes to sever its link to the server. Any subsequent invocations by the server will result in client timeout exceptions. This method also calls notify(), in case there was an invocation in process when this happened. Note: it would not make sense to call this method more than once, ever, for a given object instance.- Throws:
NoSuchObjectException
- Should this method ever be called more than once, on the same object.
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invoke
This method serves two fundamentally different, but symmetrical purposes. Initially a remoteItemProxy
calls this method to have its calling thread blocked until the server item needs to make an asynchronous callback. Secondly, the server item will also invoke this method, and will have its thread blocked, until the resulting data, or exception, is returned from the firewalled client, via its ItemProxy.- Specified by:
invoke
in interfaceInvoke
- Parameters:
method
- The name of the method on the firewalled remote client to be invoked asynchronously.args
- The data to be provided the method of the callback method, or data resulting from the client callback.- Returns:
- The result of the client object callback.
- Throws:
InterruptedException
- If the client is not listening, or if the callback timeout has expired.RemoteException
- For any network related failures.Exception
- For any client specific reasons.
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