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.

  • 1
    $\begingroup$ One username comes to my mind :) $\endgroup$ Oct 4, 2015 at 0:17
  • $\begingroup$ @belisarius yes... some friend, that as you, has more than 70k points. $\endgroup$
    – Murta
    Oct 4, 2015 at 0:22
  • $\begingroup$ Well, the code in RLink pretty much shows how this can be used. The only missing piece is the logger instance, which is referred there as RLinkInit`rlogger, and for which instead you can use Logger`getLogger["YourApp"]. And you will have to first LoadJavaClass["org.apache.log4j.Logger"], and add the log4j.jar to the classpath. $\endgroup$ Oct 4, 2015 at 0:24
  • $\begingroup$ @LeonidShifrin, interesting. Now I'm a little more comfortable with Java and Mathematica. I'll make some tests. tks $\endgroup$
    – Murta
    Oct 4, 2015 at 0:30
  • $\begingroup$ I will post a minimal code, in a moment. $\endgroup$ Oct 4, 2015 at 0:39

1 Answer 1


Minimal code

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


Here is the code:

  Block[{trace, debug, info, warn, error, fatal},
      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:

initLogger[logger_, 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):


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:

  If[i < 5, 
    logIt[logger, "i = " <> ToString [i]], 
    logIt[logger, "fatal error", "FATAL"]; Break[]
  {i, 1, 10}


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.

  • $\begingroup$ Tks a lot! Works like a charm! +1 $\endgroup$
    – Murta
    Oct 4, 2015 at 1:07
  • $\begingroup$ @Murta Glad to help, as usual. Thanks for the accept! $\endgroup$ Oct 4, 2015 at 13:11
  • 1
    $\begingroup$ @Murta Of course, the real reason why I used log4j in RLink is that I could append to the logger on both Mathematica and Java sides of RLink. If you only need Mathematica - side, you can simply use appending to a file. But for the hybrid Java / Mathematica apps, being able to use one and the same logger for both sides is important. The way you do this is to have a logger be a field of some Java class on the Java side, and then pass that instance to Mathematica. For RLink, the logger is a (static) field of RLinkInit class , accessed via RLinkInit`rlogger in Mathematica. $\endgroup$ Oct 4, 2015 at 15:07

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.