Apache Commons Logging

Apache Commons Logging

Company type	Software framework
Industry	Software development
Founder	Apache Software Foundation
Products	Java logging framework and programming interface
Owner	Apache Software Foundation
Website	https://commons.apache.org/proper/commons-logging/

Apache Commons Logging—previously known as Jakarta Commons Logging or JCL—is a logging framework and programming interface for Java, created by the Apache Software Foundation. It provides APIs, various logging implementations, and adapter wrappers that facilitate seamless integration with multiple logging systems within Java applications.

Log level

The following table presents the log levels defined by Apache Commons Logging, arranged from highest to lowest severity:

Level	Explanation
fatal	Critical errors that cause immediate shutdown; these are prominently displayed on status consoles.
error	Runtime exceptions or unforeseen conditions; also shown on status consoles.
warn	Usage of deprecated APIs, improper API utilization, or runtime events that are undesirable but not critical; visible on status consoles.
info	Significant runtime occurrences such as application startup or shutdown; visible on consoles but should be kept minimal.
debug	Comprehensive details about system operations; generally recorded in logs only.
trace	The most granular level of information; logged exclusively.

Configuration

The architecture of Apache Commons Logging revolves around two primary abstractions: Log and LogFactory.

Example

Below is an example in Java illustrating a common usage pattern:

<syntaxhighlight lang="Java"> package com.cascadetg.ch09;

import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.apache.commons.logging.impl.Jdk14Logger;

public class LogGenerator {

 private static Log log = LogFactory.getLog(LogGenerator.class);

 public static void configureJDKLogger()
 {
   try
   {
     ((Jdk14Logger)log).getLogger().setLevel(java.util.logging.Level.ALL);
     ((Jdk14Logger)log).getLogger().addHandler(
       (java.util.logging.FileHandler)Class.forName("java.util.logging.FileHandler").newInstance());

     System.out.println("Added JDK 1.4 file handler");
   } catch (Exception e)
   {
     System.out.println("Failed to load JDK 1.4 logging.");
     e.printStackTrace();
   }
 }

 public static void main(String[] args)
 {
   configureJDKLogger();
   System.setErr(System.out);

   System.out.println("\nTesting fatal log");
   try
   {
     String foo = null;
     int x = 0 / (new Integer(foo)).intValue();
   } catch (Exception e)
   {
     log.fatal(e.getMessage(), e);
   }

   System.out.println("\nTesting error log");
   try
   {
     Object foo = null;
     foo.toString();
   } catch (Exception e)
   {
     log.error(e.getMessage(), e);
   }

   System.out.println("\nTesting warn log");
   try
   {
     Class.forName("com.cascadetg.NonexistentClass");
   } catch (Exception e)
   {
     log.warn("Unable to locate nonexistent class!");
   }

   System.out.println("\nTesting info log");
   log.info("Application starting!");
   log.info("Application shutting down!");

   System.out.println("\nTesting debug log");
   if (1 > 2)
   {
     log.debug("Condition 1 > 2 evaluated as true");
     if (10 % 2 == 0)
       log.debug("10 modulo 2 equals 0");
     else
       log.debug("10 modulo 2 does not equal 0");
   } else
   {
     log.debug("Condition 1 > 2 evaluated as false");
   }

   System.out.println("\nTesting trace log");
   for (int i = 0; i < 5; i++)
     log.trace("Executing trace method.");

   System.out.println("\nLogging test completed.");
 }

} </syntaxhighlight>

See also

• log4j
• Chainsaw (log viewer)