Java Basic Util - Java Util Logging

1 Copied from source.

Hierarchical Loggers

Loggers are organized in a hierarchical namespace. The recommended namespace should follow the package naming style of the Java classes. For example we can create loggers with following names:
Logger1 > "com.logicbig"
Logger2 > "com.logicbig.MyClass2" > parent namespace= "com.logicbig"
Logger3 > "com.logicbig.MyClass3" > parent namespace= "com.logicbig"

In above example Logger1 is the parent of Logger2 and Logger3. If we setup Logger1 with specific properties (Level, Handler, Formatter etc) then those properties will be inherited to their children. A child is free to setup it's own properties to selectively override the parent ones.

An application will always has a 'root' logger. The root Logger (named "") has no parent.

Configuration, Setting up logging properties

We can load logging properties in one of following ways (in the order of priority):

1. Using JVM system property: java.util.logging.config.class=com.logicbig.example.MyConfigClass.
   Java will load MyConfigClass during startup. The constructor of this class can use following method to initialize logging properties:

   LogManager.getLogManager().readConfiguration(InputStream);

   In this initializing class, we can also setup base/individual Loggers like this:

   Logger mainLogger = Logger.getLogger("com.logicbig.example");
   mainLogger.setLevel(Level.FINEST);
   mainLogger.addHandler(....);
    ....        

2. Using JVM system property: java.util.logging.config.file = D:\myApp\logging.properties . Please see next for the format of such file.
   
3. If neither of the above properties is defined then LogManager will use lib/logging.properties in the Java installation directory.
   For example C:\Java\jdk1.8.0_111\jre\lib\logging.properties:

   ############################################################
   #  	Default Logging Configuration File
   #
   # You can use a different file by specifying a filename
   # with the java.util.logging.config.file system property.
   # For example java -Djava.util.logging.config.file=myfile
   ############################################################
   
   ############################################################
   #  	Global properties
   ############################################################
   
   # "handlers" specifies a comma separated list of log Handler
   # classes.  These handlers will be installed during VM startup.
   # Note that these classes must be on the system classpath.
   # By default we only configure a ConsoleHandler, which will only
   # show messages at the INFO and above levels.
   handlers= java.util.logging.ConsoleHandler
   
   # To also add the FileHandler, use the following line instead.
   #handlers= java.util.logging.FileHandler, java.util.logging.ConsoleHandler
   
   # Default global logging level.
   # This specifies which kinds of events are logged across
   # all loggers.  For any given facility this global level
   # can be overriden by a facility specific level
   # Note that the ConsoleHandler also has a separate level
   # setting to limit messages printed to the console.
   .level= INFO
   
   ############################################################
   # Handler specific properties.
   # Describes specific configuration info for Handlers.
   ############################################################
   
   # default file output is in user's home directory.
   java.util.logging.FileHandler.pattern = %h/java%u.log
   java.util.logging.FileHandler.limit = 50000
   java.util.logging.FileHandler.count = 1
   java.util.logging.FileHandler.formatter = java.util.logging.XMLFormatter
   
   # Limit the message that are printed on the console to INFO and above.
   java.util.logging.ConsoleHandler.level = INFO
   java.util.logging.ConsoleHandler.formatter = java.util.logging.SimpleFormatter
   
   # Example to customize the SimpleFormatter output format
   # to print one-line log message like this:
   #     <level>: <log message> [<date/time>]
   #
   # java.util.logging.SimpleFormatter.format=%4$s: %5$s [%1$tc]%n
   
   ############################################################
   # Facility specific properties.
   # Provides extra control for each logger.
   ############################################################
   
   # For example, set the com.xyz.foo logger to only log SEVERE
   # messages:
   com.xyz.foo.level = SEVERE

2 Copy the properties file from JRE folder.(e.g. C:\Java\jdk1.8.0_111\jre\lib\logging.properties) to project  (e.g.  MyProject/resources/logging.properties)

3 Modify it in your way.

4 Create the log util class as below:

package basic.util.log;

import java.text.SimpleDateFormat;

import java.util.Calendar;

import java.util.logging.FileHandler;

import java.util.logging.Level;

import java.util.logging.Logger;

import java.util.logging.SimpleFormatter;

public class Log {

  private static Logger LOGGER;

  

  private static FileHandler fh = null;

  

  static {

      String path = Log.class.getClassLoader()

                  .getResource("logging.properties")

                  .getFile();

          System.setProperty("java.util.logging.config.file", path);

          

      LOGGER = Logger.getLogger(Logger.class.getName());

      

          SimpleDateFormat format = new SimpleDateFormat("yyyy-M-d_HHmmss");

          try {

          //String currPath = Log.class.getClass().getResource("/").getPath().replaceFirst("/", "");

          String currPath = System.getProperty("user.dir") + "/Log";

              fh = new FileHandler(currPath + format.format(Calendar.getInstance().getTime()) + ".log");

          } catch (Exception e) {

              e.printStackTrace();

          }

          fh.setFormatter(new SimpleFormatter());

          LOGGER.addHandler(fh);

         

  }

  

  public static void severe(Throwable throwable) {

  severe(throwable.getLocalizedMessage(), throwable);

  }

  

  public static void severe(String msg, Throwable throwable) {

  LOGGER.log(Level.SEVERE, throwable.getLocalizedMessage(), throwable);

  }

  

  public static void info(String msg) {

  LOGGER.info(msg);

  }

  

  public static void log(String msg) {

  LOGGER.finest(msg);

  }

  public static void main(String[] args) {

  System.out.println(Log.class.getClassLoader()

                  .getResource("logging.properties")

                  .getFile());

  System.out.println(Log.class.getClass().getResource("/")

  .getFile() );

  ;

      System.out.println("-- main method starts --");

      LOGGER.info("an info msg");

      LOGGER.warning("a warning msg");

      LOGGER.severe("a severe msg");

      System.out.println("-- main method end --");

  }

}