Package gnu.cajo.utils.extra
Class ItemProxy
- java.lang.Object
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- java.lang.Thread
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- gnu.cajo.utils.extra.ItemProxy
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- All Implemented Interfaces:
java.lang.Runnable
public final class ItemProxy extends java.lang.Thread
This class is used to receive server item callbacks by a firewalled client. A client whose firewall settings prohibit incoming socket connections is a common problem. To solve this, a client would request a remote reference to aClientProxy
from the server. It would then use an ItemProxy to link the remote item to the local client item. This class is a special purpose thread, which will make an outgoing call to the remote ClientProxy. This outgoing call will be blocked until the server has some data for it, at which point it will wake this thread, causing it to return with the callback method to be invoked on the local client object, and the data to be provided it. This object will call its local client, and return the resulting data, or exception to the server. This will result in this thread being put back to sleep again, until there is another callback. This lets local client objects be designed without regard for whether they will be behind a firewall or not. This technique enables asynchronous server callbacks using the client's outgoing socket, thereby solving the firewall issue. The development of this process was originally championed by project member Fredrik Larsen.Normally, a client would not invoke a method on the remote reference it receives to the server's ClientProxy object. However, if the client wishes to forcibly terminate its connection with the server, it can invoke a no-arg cutOff method on the reference. (See the note below)
Note: The server could cut its connection to the client at any time, either intentionally by invoking its cutOff method, or worse, by a server crash. If the client wishes to be notified of this event, it must define a null argument method called cutOff. This will be invoked by the ItemProxy, in that event the cutOff method must accept a single argument, of type Exception, it will describe the reason behind the disconnection. A practical usage example is available online.- Version:
- 1.0, 28-Mar-04 Initial release
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Constructor Summary
Constructors Constructor Description ItemProxy(RemoteInvoke item, java.lang.Object client)
The constructor links the remote object to the firewalled client.
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description void
run()
The processing thread, and the crux of this technique.-
Methods inherited from class java.lang.Thread
activeCount, checkAccess, clone, countStackFrames, currentThread, dumpStack, enumerate, getAllStackTraces, getContextClassLoader, getDefaultUncaughtExceptionHandler, getId, getName, getPriority, getStackTrace, getState, getThreadGroup, getUncaughtExceptionHandler, holdsLock, interrupt, interrupted, isAlive, isDaemon, isInterrupted, join, join, join, onSpinWait, resume, setContextClassLoader, setDaemon, setDefaultUncaughtExceptionHandler, setName, setPriority, setUncaughtExceptionHandler, sleep, sleep, start, stop, suspend, toString, yield
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Constructor Detail
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ItemProxy
public ItemProxy(RemoteInvoke item, java.lang.Object client)
The constructor links the remote object to the firewalled client. It will automatically start the thread, which will call the remoteClientProxy
, blocking until there is a callback method to be invoked.- Parameters:
item
- A remote reference to a ClientProxy, from which the remote object will invoke asynchronous callbacksclient
- The firewalled local object that wishes to receive asynchronous callbacks
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Method Detail
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run
public void run()
The processing thread, and the crux of this technique. This thread starts out by calling the remoteClientProxy
, to enter a blocking wait. The ClientProxy will wake the thread, providing it an object array containing two things; the name of the method to be called on the local object, and the data to be provided it. This thread will invoke the local object's method, and return the result, or exception, to the ClientProxy, beginning the cycle again.- Specified by:
run
in interfacejava.lang.Runnable
- Overrides:
run
in classjava.lang.Thread
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