h1. Logging
h2. Introduction
Logging in Sling is supported by the {{org.apache.sling.log}} bundle, which is one of the first bundles installed and started by the Sling Launcher. The {{org.apache.sling.log}} bundle has the following tasks:
* Implements the OSGi Log Service Specification and registers the {{LogService}} and {{LogReader}} services
* Exports three logging APIs:
** [Apache Commons Logging|http://jakarta.apache.org/commons/logging]
** [Simple Logging Facade for Java (SLF4J)|http://www.slf4j.org]
** [Log4J|http://logging.apache.org/log4j/]
* Configures logging through Log4J
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h2. Initial Configuration
The {{org.apache.sling.log}} bundle gets the initial configuration from the following {{BundleContext}} properties:
| *Property* | *Default* | *Description* |
| {{org.apache.sling.log.intialize}} | {{true}} | Initial configuration property specifying whether LOG4J should be initialized here or not. If this property is missing or set to {{true}}, this class will reset and configure LOG4J. Otherwise, LOG4J is neither reset nor configured by this class. This property may be used to prevent resetting LOG4J which might be configured by a container and reused by the Framework. Setting this property to anything but {{true}} causes the other properties to be ignored. |
| {{org.apache.sling.log.level}} | {{WARN}} | Sets the initial logging level of the root logger. This may be any of the defined logging levels, which are by default {{DEBUG}}, {{INFO}}, {{WARN}}, {{ERROR}} and {{FATAL}}. |
| {{org.apache.sling.log.file}} | undefined | Sets the log file to which log messages are written. If this property is empty or missing, log messages are written to {{System.out}}. |
| {{org.apache.sling.log.pattern}} | {{{%d\{dd.MM.yyyy HH:mm:ss\} !\*%-5p\* %c\{1\}: %m%n}}} | The logging pattern to be set for the {{PatternLayout}} of root logger appender. |
| {{org.apache.sling.log.url}} | undefined | If this property is set to an URL pointing to an existing configuration file, {{level}}, {{file}} and {{pattern}} properties are ignored. |
h2. User Configuration
User Configuration after initial configuration is provided by the Configuration Admin Service. To this avail a {{org.osgi.services.cm.ManagedService}} is registered under the PID {{org.apache.sling.log.service}} which may receive configuration. Configuration through the Configuration Admin Service is still under development. Hence this section cannot be completed as of now.