Getting caller class name for Formatter [Java Logging with File Handler]

Question

I want to add a FileHandler to my logger. And I am also creating a new Formatter(java.util.logging.Formatter) for my FileHandler

In the format method https://docs.oracle.com/javase/7/docs/api/java/util/logging/Formatter.html#format(java.util.logging.LogRecord), is it possible to get the class which called the log https://docs.oracle.com/javase/7/docs/api/java/util/logging/Logger.html#log(java.util.logging.Level,%20java.lang.String)method?

Edit: I wrapped my logger in a class, so getSourceClassName() will not work

sure. Use a stack(trace), or, pass it to the logger as parameter. — Stultuske, Jan 12 '18 at 09:45
I can't pass it to the logger as parameters because im calling addHandler on a logger from a library — Ian Lim, Jan 12 '18 at 09:46
read the stacktrace, and get the 2nd StackElement (I think it's the second) and get the class from that element — Stultuske, Jan 12 '18 at 09:50
If you mean Thread.currentThread().getStackTrace() or any other stack trace. Im trying to avoid them because they are inefficient and expensive — Ian Lim, Jan 12 '18 at 09:51
Typically the loggers are named after the class they're logging - eg. private static Logger logger = Logger.getLogger("com.wombat.nose"); In this case, you should be able to use logRecord.getLoggerName(). — racraman, Jan 12 '18 at 09:56

jmehrens · Accepted Answer · 2018-01-16T15:40:19.443

...is it possible to get the class which called the log? Note that LogRecord.getSourceClassName() returns the Logger class.

LogRecord.getSourceClassName() does exactly what you want it to do. Here is an example:

import java.io.File;
import java.io.IOException;
import java.util.logging.FileHandler;
import java.util.logging.Formatter;
import java.util.logging.Level;
import java.util.logging.LogRecord;
import java.util.logging.Logger;

public class FileHandlerTest {

    private static final Logger logger = Logger.getLogger("tester");

    static {
        try {
            FileHandler h = new FileHandler();
            logger.addHandler(h);
            h.setFormatter(new TestFormatter());
        } catch (IOException ex) {
            throw new ExceptionInInitializerError(ex);
        }
    }

    private static class TestFormatter extends Formatter {

        @Override
        public String format(LogRecord record) {
            return record.getSourceClassName();
        }

    }

    public static void main(String[] args) throws Exception {
        System.out.println(new File(".").getCanonicalPath());
        System.out.println(System.getProperty("user.home"));
        logger.log(Level.INFO, "This not a test. This is the real thing!");
    }
}

When I run this on my machine it creates a file called java0.log in my user home containing the text FileHandlerTest which is the name of the source class.

There are a few reason I can think as to why it wouldn't work:

There was a hand off to another thread and you didn't call LogRecord.getSourceClassName() before the hand off. This causes the log record to infer the wrong caller.
You created a 'wrapper' class to perform your logging and the logger reports the 'wrapper' class as the caller. Don't do this. Use the logger directly or use a logging framework. There are plenty of logging bridges out there and anything you will create is going to be a pirate ship plank. That said, the com.sun.mail.util.MailLogger contains the code that all of the user comments have been trying to explain to you.
The record was generated with logp or setSourceClassName and the source class was faked.
There was a problem with your JVM generating exceptions with stack traces.

You need to include more source code and example log file output data.

@IanLim So does my project above and it functions. Include a test case that mimics the project and reproduces the problem. — jmehrens, Jan 15 '18 at 14:06
Oops I didnt noticed my library had wrapped my logger. What to do?? — Ian Lim, Jan 16 '18 at 09:13
@IanLim The short answer is don't wrap the logger. I've updated the answer for the long version. — jmehrens, Jan 16 '18 at 21:08

Getting caller class name for Formatter [Java Logging with File Handler]

1 Answers1