Java Util Logging - Customizing log format

[Updated: May 25, 2017, Created: May 18, 2017]

By default Java Util logging (JUL) uses following configurations (JDK 8):

handlers= java.util.logging.ConsoleHandler
.level= INFO
java.util.logging.ConsoleHandler.level = INFO
java.util.logging.ConsoleHandler.formatter = java.util.logging.SimpleFormatter

The complete default configuration file can be found at the JDK/JRE installation directory: JAVA_HOME/jre/lib/logging.properties.

The default handler, ConsoleHandler, sends log records to System.err (the available command line console). This handler, by default uses SimpleFormatter to format logs. In this tutorial, we will learn how to modify the default log format.

The default formatter, SimpleFormatter, formats the output by using following method call:

 String.format(format, date, source, logger, level, message, thrown);

The first argument 'format' can be customized in the logging.properties or by a command line option or can be set programmatically. The good thing, we don't have to learn new formatting specifiers here, as java.util.Formatter specification is fully supported.

Using logging.properties

Let's add a new line to logging.properties with property key
java.util.logging.SimpleFormatter.format to specify our desire log format.

src/main/resources/logging.properties

handlers= java.util.logging.ConsoleHandler
.level= INFO
java.util.logging.ConsoleHandler.level = INFO
java.util.logging.ConsoleHandler.formatter = java.util.logging.SimpleFormatter
java.util.logging.SimpleFormatter.format=[%1$tF %1$tT] [%4$-7s] %5$s %n
public class MyClass {
  private static Logger LOGGER = null;

  static {
      InputStream stream = MyClass.class.getClassLoader().
              getResourceAsStream("logging.properties");
      try {
          LogManager.getLogManager().readConfiguration(stream);
          LOGGER= Logger.getLogger(MyClass.class.getName());

      } catch (IOException e) {
          e.printStackTrace();
      }
  }

  public static void main(String[] args) {
      System.out.println("-- main method starts --");
      LOGGER.info("in MyClass");
      LOGGER.warning("a test warning");
  }
}

Output

-- main method starts --
[2017-05-18 14:02:49] [INFO ] in MyClass
[2017-05-18 14:02:49] [WARNING] a test warning

Check this out to quickly learn different time formatting options

Using system property

public class MyClass2 {
  private static Logger LOGGER = null;

  static {
      System.setProperty("java.util.logging.SimpleFormatter.format",
              "[%1$tF %1$tT] [%4$-7s] %5$s %n");
      LOGGER = Logger.getLogger(MyClass2.class.getName());
  }

  public static void main(String[] args) {
      System.out.println("-- main method starts --");
      LOGGER.info("in MyClass2");
      LOGGER.warning("a test warning");
  }
}

Output

-- main method starts --
[2017-05-18 14:03:41] [INFO ] in MyClass2
[2017-05-18 14:03:41] [WARNING] a test warning

Programmatically setting format

Here we have to set our own ConsoleHandler with customized SimpleFormatter instead of customizing the default one.

package com.logicbig.example;

import java.util.Date;
import java.util.logging.ConsoleHandler;
import java.util.logging.LogRecord;
import java.util.logging.Logger;
import java.util.logging.SimpleFormatter;

public class MyClass3 {
  private static Logger LOGGER = null;

  static {
      Logger mainLogger = Logger.getLogger("com.logicbig");
      mainLogger.setUseParentHandlers(false);
      ConsoleHandler handler = new ConsoleHandler();
      handler.setFormatter(new SimpleFormatter() {
          private static final String format = "[%1$tF %1$tT] [%2$-7s] %3$s %n";

          @Override
          public synchronized String format(LogRecord lr) {
              return String.format(format,
                      new Date(lr.getMillis()),
                      lr.getLevel().getLocalizedName(),
                      lr.getMessage()
              );
          }
      });
      mainLogger.addHandler(handler);
      LOGGER = Logger.getLogger(MyClass3.class.getName());
  }

  public static void main(String[] args) {
      System.out.println("-- main method starts --");
      LOGGER.info("in MyClass3");
      LOGGER.warning("a test warning");
  }
}

Output

-- main method starts --
[2017-05-18 14:04:07] [INFO ] in MyClass3
[2017-05-18 14:04:07] [WARNING] a test warning

Example Project

Dependencies and Technologies Used :

  • JDK 1.8
  • Maven 3.3.9

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See Also