Java Tutorial/Log/Log Level

Comparing Log Levels: To compare the severity of two logging levels, use Level.intValue().

   <source lang="java">

import java.util.logging.Level; public class Main {

 public static void main(String[] argv) throws Exception {
   Level level1 = Level.INFO;
   Level level2 = Level.CONFIG;
   if (level1.intValue() > level2.intValue()) {
     System.out.println("level1 is more severe");
   } else if (level1.intValue() < level2.intValue()) {
     System.out.println("level2 is more severe");
   } else {
     System.out.println("level1 == level2");
   }
 }

}</source>

Creating a Custom Log Level

   <source lang="java">

import java.util.logging.Level; import java.util.logging.Logger; class MyLevel extends Level {

 public static final Level DISASTER = new MyLevel("DISASTER", Level.SEVERE.intValue() + 1);
 public MyLevel(String name, int value) {
   super(name, value);
 }

} public class Main {

 public static void main(String[] argv) throws Exception {
   Logger logger = Logger.getLogger("com.mycompany");
   logger.log(MyLevel.DISASTER, "my disaster message");
   Level disaster = Level.parse("DISASTER");
   logger.log(disaster, "my disaster message");
 }

}</source>

Determining If a Message Will Be Logged

   <source lang="java">

import java.util.logging.Level; import java.util.logging.Logger; public class Main {

 public static void main(String[] argv) throws Exception {
   Logger logger = Logger.getLogger("com.mycompany.MyClass");
   // Check if the message will be logged
   if (logger.isLoggable(Level.FINEST)) {
     logger.finest("my finest message");
   }
 }

}</source>

Getting the Log Level of a Logger

   <source lang="java">

import java.util.logging.Level; import java.util.logging.Logger; public class Main {

 public static void main(String[] argv) throws Exception {
 }
 // Return the level of the specified logger.
 public static Level getLevel(Logger logger) {
   Level level = logger.getLevel();
   while (level == null && logger.getParent() != null) {
     logger = logger.getParent();
     level = logger.getLevel();
   }
   return level;
 }

}</source>

Log finest, finer, config, warning ans severe

   <source lang="java">

import java.util.logging.Logger; public class Logging {

 public static void main(String[] args) {
   Logger log = Logger.getLogger("global");
   log.finest("A");
   log.finer("B");
   log.fine("C");
   log.config("D");
   log.info("E");
   log.warning("O");
   log.severe("A");
 }

}</source>

Setting the Log Level of a Logger

   <source lang="java">

import java.util.logging.Level; import java.util.logging.Logger; public class Main {

 public static void main(String[] argv) throws Exception {
   // Get a logger
   Logger logger = Logger.getLogger("com.mycompany");
   // Set the level to a particular level
   logger.setLevel(Level.INFO);
   // Set the level to that of its parent
   logger.setLevel(null);
   // Turn off all logging
   logger.setLevel(Level.OFF);
   // Turn on all logging
   logger.setLevel(Level.ALL);
 }

}</source>

Use different logging level

   <source lang="java">

import java.util.logging.Level; import java.util.logging.Logger; public class MainClass {

 private static Logger
   lgr = Logger.getLogger("com"),
   lgr2 = Logger.getLogger("com.jexp"),
   util = Logger.getLogger("com.jexp.util"),
   test = Logger.getLogger("com.jexp.test"),
   rand = Logger.getLogger("random");
   
 private static void logMessages() {
   lgr.info("com : info");
   lgr2.info("com.bruceeckel : info");
   util.info("util : info");
   test.severe("test : severe");
   rand.info("random : info");
 }
 public static void main(String[] args) {
   lgr.setLevel(Level.SEVERE);
   System.out.println("com level: SEVERE");
   logMessages();
   util.setLevel(Level.FINEST);
   test.setLevel(Level.FINEST);
   rand.setLevel(Level.FINEST);
   System.out.println("individual loggers set to FINEST");
   logMessages();
   lgr.setLevel(Level.SEVERE);
   System.out.println("com level: SEVERE");
   logMessages();
 }

}</source>