Handling Exceptions and Debugging - Beginning Java Programming: The Object-Oriented Approach - page 204

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FINER: finer detailed message
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FINE: fine detailed message
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CONFIG: configuration message
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INFO: informational message
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WARNING: warning message
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SEVERE: severe message
The contents of the config log file look like this:
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INFO: fundAmount = 11000.0
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INFO: fundAmount = 11000.0
Aug 12, 2014 5:54:43 PM chapter6.LoggerExample recalculate
INFO: fundAmount = 11000.0
Aug 12, 2014 5:54:43 PM chapter6.LoggerExample recalculate
INFO: fundAmount = 11000.0
Aug 12, 2014 5:54:43 PM chapter6.LoggerExample recalculate
INFO: fundAmount = 11000.0
Aug 12, 2014 5:54:43 PM chapter6.LoggerExample recalculate
INFO: fundAmount = 11000.0
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SEVERE: monthlyPension is too low.
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CONFIG: configuration message
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INFO: informational message
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WARNING: warning message
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SEVERE: severe message
Naturally, there are many more messages in the finer log file, because it includes more levels
(particularly, the entering and exiting messages, which are defined as finer level messages). Also,
note that neither log contains the “finest detailed message” from the main method. This is too
low level for the finer logger to log. You can see again here that the fundAmount is 11000 every
time the method is called, again suggesting that the value is not being stored and used in future
calculations. But you can see for sure that the method is being entered and exited as expected.
This leads to the same conclusion (and fix) as before, but logging allows ongoing monitoring of
live applications. Simply by increasing the level of the logger, you can control how many and what
types of messages are logged.
So far, you've only seen the built‐in logger, but Log4j is a popular alternative logger. The Log4j
utility has been in use for 15 years, but Apache Log4j 2 was released in 2014. It offers high perfor-
mance, flexibility, and usability, and is well worth your consideration when deciding on a logging
utility. You can download Log4j 2 at http://logging.apache.org/log4j/2.x/index.html .