Subclassing java.util.logging.Formatter doesn't work

Question

I am using java.util.logging for logging (I don\'t want to use log4j or anything else).

This is my complete private logging.properties:

Answer 1

You can set the formatter in the code itself on the FileHandler instance.

import java.util.logging.FileHandler;
import java.util.logging.Level;
import java.util.logging.Logger;

// please change name of your own choice
Logger log = Logger.getLogger("CustomLogger"); 
log.setUseParentHandlers(false);
log.setLevel(Level.ALL);

FileHandler handler = new FileHandler("[log_file_location]");
handler.setFormatter(new CustomFormatter()); // set formatter
log.addHandler(handler);

log.info("test message");

handler.close(); // close the handler at some later point in your application.

The CustomFormatter class is defined as follows.

import java.util.logging.Formatter;
import java.util.logging.LogRecord;

public class CustomFormatter extends Formatter {

    @Override
    public String format(LogRecord record) {
        StringBuffer buffer = new StringBuffer();
        buffer.append(record.getMessage());
        return buffer.toString();
    }

}

You can code in CustomFormatter to output the messages in any format you want. Hope this helps.

Answer 2

com.mycomp.myproj.LogFormatter is not in your system class path.

LogManager will do the following call for loading your class:

Formatter getFormatterProperty(String name, Formatter defaultValue) {
        String val = getProperty(name);
        try {
            if (val != null) {
                Class<?> clz = ClassLoader.getSystemClassLoader().loadClass(val);
                return (Formatter) clz.newInstance();
            }
        } catch (Exception ex) {
            // We got one of a variety of exceptions in creating the
            // class or creating an instance.
            // Drop through.
        }
        // We got an exception.  Return the defaultValue.
        return defaultValue;
}

You need to make sure your class LogFormatter is in the system's class path.

Answer 3

I found that unless you set the format via the config, it does not apply the formatter. I tested this on JDK 11.

handlers= java.util.logging.FileHandler
.level= INFO
java.util.logging.FileHandler.pattern = my.log
java.util.logging.FileHandler.limit = 500000
java.util.logging.FileHandler.count = 40
java.util.logging.FileHandler.formatter = com.mycomp.myproj.LogFormatter
com.mycomp.myproj.LogFormatter.format = %n

i.e. add the last line com.mycomp.myproj.LogFormatter.format = %n

Answer 4

Ok this one really annoyed me too, and was driving me nuts, I was checking the spelling endlessly, doing google searching etc - which is how I got here - I know this is a year old, but your going to kick yourself. Here is what I am pretty sure is your answer.

For :

java.util.logging.FileHandler.formatter = com.mycomp.myproj.LogFormatter;

That should be :

java.util.logging.FileHandler.formatter = com.mycomp.myproj.LogFormatter

Drop the training ";". It seems to need to match exactly to the class name I saw someone else complain they had trailing white space characters - which was what my problem was. A better error message would have been helpful.

Cheers - Mark

Answer 5

How do I figure out why FileHandler isn't using my LogFormatter class?

Start the program in a debugger and step through the code. Set a breakpoint in LogManager.getLogger() and/or LogManager.readConfiguration()

Or forget about java.util.logging and use a framework like logback that is easy to configure and gives you useful error messages when something is wrong.