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From <david.g...@hic.gov.au>
Subject LogKit: Support for fail-safe operations
Date Tue, 16 Oct 2001 00:18:47 GMT

I have been looking for a logging framework which will notify the client
application
when logging fails (fail-safe). I am seeking confirmation that Logkit can
achieve this.
Having looked at the source code, Logkit defaults to using
DefaultErrorHandler
which does not, by itself, ensure fail-safe operations.

However, if I subclass DefaultErrorHandler and make the error method throw
a
run-time exception, this should then allow any client class to detect the
failure
and take appropriate action. Naturally, the client will need to instantiate
a Hierarchy object that sets the ErrorHandler.

My question is - this seems very easy to do but will this work?

==== Source Code follows FailSafeErrorHandler.java
====

import org.apache.log.util.DefaultErrorHandler;
import org.apache.log.LogEvent;
/**
 * Insert the type's description here.
 * Creation date: (11/10/2001 17:19:59)
 * @author: David Gray
 */
public class FailSafeErrorHandler extends DefaultErrorHandler {
public FailSafeErrorHandler () {
     super();
}
public void error(
   final String message,
   final Throwable throwable,
   final LogEvent event) {
   super.error(message, throwable, event);
   throw new LoggingException(message);
}
}

===== I have defined the class LoggingException so that clients can specifically catch it.


/**
 * Insert the type's description here.
 * Creation date: (12/10/2001 9:03:18)
 * @author: David Gray
 */
public class LoggingException extends RuntimeException {
/**
 * LoggingException constructor comment.
 */
public LoggingException() {
     super();
}
/**
 * LoggingException constructor comment.
 * @param s java.lang.String
 */
public LoggingException(String s) {
     super(s);
}
}

===== I Tested this setup with the following code (under jUnit hence the call to fail() ).
Note, that the code
creates an instance of the Hierarchy Class:

public void testHICErrorHandler() {
   FailSafeErrorHandler hicErrorHandler = new FailSafeErrorHandler();
   Hierarchy h = new Hierarchy();
   h.setErrorHandler(hicErrorHandler);
   Logger logger = h.getLoggerFor("mySafeCategory");
   logger.setPriority(Priority.DEBUG);
   PriorityFilter filter = new PriorityFilter(Priority.ERROR);
   final String pattern =
      "%7.7{priority} %5.5{time}   [%8.8{category}] "
         + "(%{context}): %{message}\\n%{throwable}";
   final PatternFormatter formatter = new PatternFormatter(pattern);
   final File file = new File("C:/temp/log.txt");
   try {
      // deleting the file ensures that the new file is
      // write enabled.
     file.delete();
     // Note - using SafeFileTarget ensures that file is opened and closed for
     // each log movement hence the write-protect can actually force an error
    SafeFileTarget target = new SafeFileTarget(file, true, formatter);
      //Set log targets of logger
      logger.setLogTargets(new LogTarget[] { target, filter });
      try {
         // The following will work
         logger.debug("This is a debug message to " + this.getName());
         file.setReadOnly();
         // If here we write-protect the file the following throws
         // the LoggingException message.
         logger.debug("This is a info message to " + this.getName());
         fail("Was able to write a message to a write-only file");
      }
      catch (LoggingException le) {
         // This should occur
      }
   }
   catch (IOException e) {
      fail("Unable to set a log file - check if read-only " + e.getMessage());
   }
}



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