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Observing JavaSpace-Based Systems, Part I
How to Log and Analyze a Space-Based Distributed System
by Philip Bishop & Nigel Warren
October 7, 2002

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A Logging JavaSpace Proxy

One main benefit of a logging system is that it lets us see how clients use the space without having to insert debug/logging statements into the client code. To automate this process without touching our client code, we will use a simple yet powerful idea.

We know that all space-based systems load a proxy at runtime to support the remote calls on the JavaSpaces API. Using this knowledge, we can easily build new proxies that hide the logging operations from the client, but still look like the standard JavaSpace proxy.

So in our system, the Jini proxy for our logging system will implement the JavaSpaces interface. However, instead of calling the backend of the JavaSpace directly, the proxy will collect the information we need and then forward the JavaSpaces API calls onto another proxy that uses the backend JavaSpaces server.

To avoid confusion, throughout this article we will call the proxy that produces logging information the logging proxy. The standard proxy that calls into the space backend is called the delegate proxy, and the combination of delegate proxy and the backend space will naturally be called the delegate space.

Figure 1 shows the general structure for building the logging proxies and using the delegate space.

Figure 1. A Logging JavaSpace Proxy Architecture.

The interface to the logging proxy, LoggingSpace, extends JavaSpace:

public interface LoggingSpace extends JavaSpace {
   // no additional methods to those in the JavaSpace interface

LoggingSpace has exactly the same methods as the JavaSpace interface. By declaring a LoggingSpace as a subinterface of JavaSpace, it can be used wherever a JavaSpace is called for. But because it is a subinterface, we can use a type-based lookup in the Jini lookup service to find a JavaSpace proxy that also does logging.

Now that we have established a general structure for the logging proxy, let's consider how we will record and structure the logging information.

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