Writing User Extensions


General Considerations

You can configure the WebSphere Application Server to use Java 2 security to restrict access to protected resources such as the file system and sockets. Since user written extensions typically access such protected resources, user written extensions must contain the appropriate security checking calls, using AccessController doPrivileged() calls. In addition, the user written extensions must contain the appropriate policy file. In general, it is recommended that you locate user written extensions in a separate package. It is your responsibility to restrict access to the user written extensions appropriately.


Writing a handler

User written handlers must implement the RASIHandler interface. The RASIHandler interface extends the RASIMaskChangeGenerator interface, which extends the RASIObject interface. A short discussion of the methods introduced by each of these interfaces follows, along with implementation pointers. For more in depth information on any of the particular interfaces or methods, see the corresponding product Javadoc.


RASIObject interface

The RASIObject interface is the base interface for stand-alone JRas logging toolkit classes that are stateful or configurable, such as loggers, handlers and formatters.


RASIMaskChangeGenerator interface

The RASIMaskChangeGenerator interface is the interface that defines the implementation methods for filtering of events based on a mask state. This means that it is currently implemented by both loggers and handlers. By definition, an object that implements this interface contains both a message mask and a trace mask, although both need not be used. For example, message loggers contain a trace mask, but the trace mask is never used since the message logger never generates trace events. Handlers however can actively use both mask values. For example a single handler could handle both message and trace events.

In addition, this interface introduces the concept of calling back to interested parties when a mask changes state. The callback object must implement the RASIMaskChangeListener interface.

For efficiency reasons, the Jras extensions message and trace loggers implement the RASIMaskChangeListener interface. The logger implementations maintain a "composite mask" in addition to the logger's own mask. The logger's composite mask is formed by logically or'ing the appropriate masks of all handlers that are registered to that logger, then and'ing the result with the logger's own mask. For example, the message logger's composite mask is formed by or'ing the message masks of all handlers registered with that logger, then and'ing the result with the logger's own message mask.

This means that all handlers are required to properly implement these methods. In addition, when a user handler is instantiated, the logger it is to be added to should be registered with the handler using the addMaskChangeListener() method. When either the message mask or trace mask of the handler is changed, the logger must be called back to inform it of the mask change. This allows the logger to dynamically maintain the composite mask.

The RASMaskChangedEvent class is defined by the stand-alone JRas logging toolkit. Direct usage of that class by user code is allowed in this context.

In addition the RASIMaskChangeGenerator introduces the concept of caching the names of all message and trace event classes that the implementing object will process. The intent of these methods is to allow a management program such as a GUI to retrieve the list of names, introspect the classes to determine the event types that they might possibly process and display the results. The JRas extensions do not ever call these methods, so they can be implemented as no operations, if desired.


RASIHandler interface

The RASIHandler interface introduces the methods that are specific to the behavior of a handler.

The RASIHandler interface as provided by the stand-alone JRas logging toolkit supports handlers that run in either a synchronous or asynchronous mode. In asynchronous mode, events are typically queued by the calling thread and then written by a worker thread. Since spawning of threads is not allowed in the WAS environment, it is expected that handlers will not queue or batch events, although this is not expressly prohibited.


Writing a formatter

User written formatters must implement the RASIFormatter interface. The RASIFormatter interface extends the RASIObject interface. The implementation of the RASIObject interface is the same for both handlers and formatters. A short discussion of the methods introduced by the RASIFormatter interface follows. For more in depth information on the methods introduced by this interface, see the corresponding product javadoc.


RASIFormatter interface