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Using Java log4j in Mathematica


Someone has a code example of how log4j can be used to create logs in Mathematica?


RLink uses it, as can be checked in initLogger[] function, in this file:


SystemOpen@FileNameJoin@{DirectoryName@DirectoryName@FindFile["RLink`"], "RLink.m"}


But it's not a stand alone code. If someone has a simpler one, I would appreciate.



Answer



Minimal code


Here is a minimal code (partly adopted from RLink), to get you started. First, load JLink:


Needs["JLink`"]
InstallJava[]

Here is the code:


ClearAll[logIt];

logIt[logger_,msg_String,mode_String]:=
Block[{trace, debug, info, warn, error, fatal},
With[{
method = mode /. {
"TRACE" -> trace,
"DEBUG" -> debug,
"INFO" -> info,
"WARN" -> warn,
"FATAL" -> fatal,
_ :> Return[$Failed, Block]

}},
JavaBlock@logger@method[JavaNew["java.lang.String", msg]]
]
];

logIt[logger_,msg_String]:=logIt[logger, msg, "INFO"];

And the initLogger function:


ClearAll[initLogger];
initLogger[logger_, logFile_]:=

Module[{},
logger@removeAllAppenders[];
logger@addAppender[
JavaNew["org.apache.log4j.ConsoleAppender"]
];
logger@addAppender[
JavaNew[
"org.apache.log4j.FileAppender",
JavaNew["org.apache.log4j.SimpleLayout"],
logFile

]
];
logIt[logger, "Logger initialized"];
];

Example of use


Here is an example (I assume that log4j is already on the classpath, which is usually so, because it is used also internally in Mathematica):


LoadJavaClass["org.apache.log4j.Logger"]

Now create a logger instance:



logger = Logger`getLogger["MyApp"]

(* « JavaObject[org.apache.log4j.Logger]» *)

and the log file:


$logFile = FileNameJoin[{$TemporaryDirectory, "mylog.txt"}];

Now, initialize the logger:


initLogger[logger, $logFile]


You can test:


Import[$logFile, "String"]

(* "INFO - Logger initialized" *)

Now log something:


Do[
If[i < 5,
logIt[logger, "i = " <> ToString [i]],
logIt[logger, "fatal error", "FATAL"]; Break[]

],
{i, 1, 10}
]

check:


Import[$logFile, "String"]

"INFO - Logger initialized
INFO - i = 1
INFO - i = 2

INFO - i = 3
INFO - i = 4
FATAL - fatal error"

You can do more interesting things with loggers with log4j, but this example should get you started.


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