Implementing logging in a Java application

Question

Disclaimer: I apologize that this question is so long. I have added code as I have explored suggestions made here and done additional research since asking my original question.

I am working on an open source project in Java and want to implement logging in my application to facilitate bug tracking and debugging when/if users report problems with the app. I am looking at the java.util.logging package from the standard Java API. I've already added some logging code when exceptions are caught. For example, I have

Logger.getLogger(FindCardsPanel.class.getName()).log(Level.SEVERE, "Storage I/O error", ex);

The only difference in each line of code is the class name and the message string.

I have read that the proper way to use a logger is using one for each class name string. This makes a little bit of sense since it allows a lot of flexibility in filtering log messages.

My current problem is that all of the logging messages currently go to stderr. I need to write them to a file instead. I have found the FileHandler class which facilitates this. However, since I have dozens of classes, I have dozens of logger names. Do I need to add the FileHandler to each of these? That seems like it will take a lot of work, especially when I decide to add another class to my code base.

I understand that there is some kind of tree hierarchy of loggers. Does this happen automatically? If not, how do I create my own hierarchy? And whether or not it's automatic, where in the hierarchy do I add my FileHandler so that all logging goes to the same file?

Edit:

Based on the link given by @spdaley, I have created the following SSCCE:

LoggingSSCCE.java:

package loggingsscce;

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

public class LoggingSSCCE {
    private static String LOG_FILE_NAME = "loggingsscce.log";

    public static void main(String[] args) throws IOException {
        LoggingSSCCE.initLogger();

        LogTest lta = new LogTestA();
        lta.doLog();

        LogTest ltb = new LogTestB();
        ltb.doLog();
    }

    private static void initLogger() throws IOException {
        FileHandler handler = null;

        try {
            boolean append = true;
            handler = new FileHandler(LoggingSSCCE.LOG_FILE_NAME, append);
            handler.setFormatter(new SimpleFormatter());

            Logger logger = Logger.getLogger("");
            logger.setLevel(Level.ALL);
            logger.addHandler(handler);
        } finally {
            handler.close();
        }
    }
}

LogTest.java:

package loggingsscce;

interface LogTest {
    public void doLog();
}

LogTestA.java:

package loggingsscce;

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

class LogTestA implements LogTest {
    @Override
    public void doLog() {
        Logger.getLogger(LogTestA.class.getName()).log(Level.INFO, "LogTestA.doLog()");
    }
}

LogTestB.java:

package loggingsscce;

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

class LogTestB implements LogTest {
    @Override
    public void doLog() {
        Logger.getLogger(LogTestA.class.getName()).log(Level.INFO, "LogTestB.doLog()");
    }
}

When I run this in NetBeans, the output window shows

run:
Sep 09, 2012 5:36:56 PM loggingsscce.LogTestA doLog
INFO: LogTestA.doLog()
Sep 09, 2012 5:36:56 PM loggingsscce.LogTestB doLog
INFO: LogTestB.doLog()
BUILD SUCCESSFUL (total time: 0 seconds)

but the "loggingsscce.log" file is empty.

So what am I missing?

Another edit:

I found an example at http://onjava.com/pub/a/onjava/2002/06/19/log.html?page=2 which I modified:

import java.io.IOException;
import java.util.logging.FileHandler;
import java.util.logging.Handler;
import java.util.logging.Level;
import java.util.logging.Logger;
import java.util.logging.LogManager;
import java.util.logging.SimpleFormatter;

public class HelloWorld {
  private static Logger theLogger = Logger.getLogger(HelloWorld.class.getName());

  public static void main( String[] args ) throws IOException {
    Logger rootLogger = Logger.getLogger("");
    Handler handler = new FileHandler("hello.log");

    handler.setFormatter(new SimpleFormatter());
    rootLogger.addHandler(handler);

    // The root logger's handlers default to INFO. We have to
    // crank them up. We could crank up only some of them
    // if we wanted, but we will turn them all up.
    Handler[] handlers = Logger.getLogger( "" ).getHandlers();
    for ( int index = 0; index < handlers.length; index++ ) {
      handlers[index].setLevel( Level.FINE );
    }

    // We also have to set our logger to log finer-grained
    // messages
    theLogger.setLevel(Level.FINE);
    HelloWorld hello = new HelloWorld("Hello world!");
    hello.sayHello();
  }

  private String theMessage;

  public HelloWorld(String message) {
    theMessage = message;
  }

  public void sayHello() {
    theLogger.fine("Hello logging!");
    System.err.println(theMessage);
  }
}

This produces the following output from the command-line:

lib_lab_ref08@LBP-REF87XVMDP1 /e/devel/src/java/stackoverflow
$ javac HelloWorld.java

lib_lab_ref08@LBP-REF87XVMDP1 /e/devel/src/java/stackoverflow
$ java HelloWorld
Sep 09, 2012 6:13:33 PM HelloWorld sayHello
FINE: Hello logging!
Hello world!

lib_lab_ref08@LBP-REF87XVMDP1 /e/devel/src/java/stackoverflow
$ cat hello.log
Sep 09, 2012 6:13:33 PM HelloWorld sayHello
FINE: Hello logging!

lib_lab_ref08@LBP-REF87XVMDP1 /e/devel/src/java/stackoverflow
$

So this single class example works just fine. What is the difference when I have multiple classes in multiple files as in my previous code?

Modifications to LoggingSSCCE class:

I added a static field:

private static FileHandler HANDLER = null;

And changed the initLogger() method:

private static void initLogger() throws IOException {
    LoggingSSCCE.HANDLER = new FileHandler(LoggingSSCCE.LOG_FILE_NAME);
    LoggingSSCCE.HANDLER.setFormatter(new SimpleFormatter());

    Logger logger = Logger.getLogger("");
    logger.setLevel(Level.ALL);
    logger.addHandler(LoggingSSCCE.HANDLER);
}

This works great with the following contents of "loggingsscce.log":

Sep 09, 2012 6:50:16 PM loggingsscce.LogTestA doLog
INFO: LogTestA.doLog()
Sep 09, 2012 6:50:16 PM loggingsscce.LogTestB doLog
INFO: LogTestB.doLog()

I'm still having trouble making this all work in my more complicated Swing project. I suspect my FileHandler is being closed, perhaps by the garbage collector?

Answer 1

The immediate thing that comes to mind is, take a look at log4j. It's an open source logging framework that's very widely used in all sorts of libraries and applications.

Edit:

java.util.logging is the basic API. It really doesn't do anything you don't tell it to do, explicitly, in code. log4j is a library with full configuration facilities and other goodies. It sits atop java.util.logging and expands it with functionality that is much easier to use than the (relatively) low-level java.util.logging.