Release Version 1.9
The jlog2 software package is a lightweight logging
application that allows you to log information relating to the
operation of your software program. The package is written in Java
under the J2ME platform and is compatible with both the CLDC and CDC
versions. This package is used by the
system, for example. The package provides functionality for logging general information or debugging
information, to different sets of streams. It is based on creating
channels to write to, and then allocating these to each logger that is
used. A channel could be anything and so could include something like a
text area GUI component, which would be written to instead of one of
the standard outputs. There are also a small number of useful utility
classes that perform some basic operations, not currently available
under the restricted J2ME platform. The package is provided as a jar file that you include
in your library and then use the relevant classes that you need.
The software package can be
from the sourceforge.net site. It comes with the
jar file (only 12k in size), source code and user guide. It is very easy to use and the
following sections outline some basic implementation details:
Initialise the Loggers
To initialise the logging, you make a call like:
And also store the logger.config
file in a local config
Create a Logger
To create a logger you need to declare a static object of type
Logger in your class code and then initialise it through a static
constructor. This logger will then be used by all instances of the
class that are created. The logger needs to be initialised with the
classname of the class it belongs to, for identification purposes. For
public class YourClass
/** The logger */
private static Logger logger;
// get the logger
logger = LoggerHandler.getLogger(YourClass.class.getName());
This would specify the logger for the YourClass class. To also output a
debug trace for the specified file, you not only need to specify the
configuration properties, but also set the debug variable for the
logger to true. This means that you can debug only specific classes -
that have the debug variable set to true. If no classes have the debug
variable set then there will be no debug output trace. To log
information, you then send the message to the LoggerHandler, for
LoggerHandler.logMessage(logger, LoggerHandler.INFO, "method",
All logging should be done through a LoggerHandler call, which should
also be used to choose the logging level.
Warning about Static Inheritance
Because the logger is static, there can be a problem if you declare the logger in a base class and
then derive a number of classes from that. For example, if you write a class:
class YourBaseClass ()
protected static Logger logger;
And then create two derived classes, in the following order:
class YourDerivedClass1 () extends YourBaseClass
logger = LoggerHandler.getLogger(YourDerivedClass1.class.getName());
class YourDerivedClass2 () extends YourBaseClass
logger = LoggerHandler.getLogger(YourDerivedClass2.class.getName());
If an error from 'YourDerivedClass1' is logged, it might be
assigned the classname of 'YourDerivedClass2', because they have been
assigned the same logger. This can be fixed by declaring a private logger in each derived
class and not in the base class.
The logger is easily configured through a logger.config
configuration file that might look like:
log.channels = FO
debug.channels = f
log.file.path = licas.log
log.file.size = 100000
log.file.backup = 5
log.level = Info
debug.file.path = licas.debug
debug.file.size = 10000
debug.file.backup = 1
debug.level = info
These are all of the entries that you might use. There are separate entries
for the logging streams and the debugging streams, starting with log.
respectively. They configure the logger as follows:
The configuration allows the user to specify default channels to log to.
These can be standard output (O), standard error (E), or a file (F).
To log to these simply specify the combination of these letters.
The file.path properties specify the file name.
Each log file has a maximum size as specified by the file.size
property. This is the maximum number of lines allowed in the log
file. When this maximum value has been reached, the file is cleared
of all entries and then filled with the new log information until
the maximum value is reached again, etc.
You can also save earlier versions of the log file that would
otherwise be overwritten when the maximum size is reached. The
number of previous files that you keep is declared by the
Logging can be declared at different levels representing different
levels of importance, using the .level entry.
The levels available in order are: All, Info,
Warn, Error, Severe, Message.
Note that the folders to read files from or write files to can now
be set through the ConfigHandler. This should make the logger more
compatible with an access-restricted mobile device.
Create Custom Loggers
You can also write your own logging channels by extending the
class and implementing the abstract methods. For example,
you could create a swing TextArea
component and choose to log to that
instead of a file. You then need to add the new channel to the
as a default channel, to allow it to be included with
every logger that is created. The documentation shows that this is
Author: Kieran Greer,
Distributed Computing Systems
For any queries about the software package, please contact the project
The awards are listed on the main DCS site.