Using java.util.logging (Default)

The default implementation of java.util.logging provided in the JDK is too limited to be useful. The key limitation is the inability to have per-web application logging, as the configuration is per-VM. As a result, Tomcat will, in the default configuration, replace the default LogManager implementation with a container friendly implementation called JULI, which addresses these shortcomings.

JULI supports the same configuration mechanisms as the standard JDK java.util.logging, using either a programmatic approach, or properties files. The main difference is that per-classloader properties files can be set (which enables easy redeployment friendly webapp configuration), and the properties files support extended constructs which allows more freedom for defining handlers and assigning them to loggers.

JULI is enabled by default, and supports per classloader configuration, in addition to the regular global java.util.logging  configuration. This means that logging can be configured at the following layers:

q  Globally

That is usually done in the ${catalina.base}/conf/logging.properties  file. The file is specified by the java.util.logging.config.file  System property which is set by the startup scripts. If it is not readable or is not configured, the default is to use the ${java.home}/lib/logging.properties  file in the JRE.

q  In the web application

The file will be WEB-INF/classes/logging.properties

The default logging.properties  in the JRE specifies a ConsoleHandler that routes logging to System.err. The default conf/logging.properties  in Apache Tomcat also adds several FileHandlers that write to files.

A handler's log level threshold is INFO by default and can be set using SEVERE, WARNING, INFO, CONFIG, FINE, FINER, FINEST or ALL. You can also target specific packages to collect logging from and specify a level.

To enable debug logging for part of Tomcat's internals, you should configure both the appropriate logger(s) and the appropriate handler(s) to use the FINEST or ALL level. e.g.:

org.apache.catalina.session.level=ALL

java.util.logging.ConsoleHandler.level=ALL

When enabling debug logging it is recommended that it is enabled for the narrowest possible scope as debug logging can generate large amounts of information.

The configuration used by JULI is the same as the one supported by plain java.util.logging, but uses a few extensions to allow better flexibility in configuring loggers and handlers. The main differences are:

q  A prefix may be added to handler names, so that multiple handlers of a single class may be instantiated. A prefix is a String which starts with a digit and ends with '.'. For example, 22foobar. is a valid prefix.

q  System property replacement is performed for property values which contain ${systemPropertyName}.

q  If using a class loader that implements the org.apache.juli.WebappProperties  interface (Tomcat's web application class loader does) then property replacement is also performed for ${classloader.webappName}, ${classloader.hostName}  and ${classloader.serviceName}  which are replaced with the web application name, the host name and the service name respectively.

q  By default, loggers will not delegate to their parent if they have associated handlers. This may be changed per logger using the loggerName.useParentHandlers  property, which accepts a Boolean value.

The root logger can define its set of handlers using the .handlers  property.

By default, the log files will be kept on the file system forever. This may be changed per handler using the handlerName.maxDays  property. If the specified value for the property is <=0 then the log files will be kept on the file system forever, otherwise they will be kept the specified maximum days.

There are several additional implementation classes, that can be used together with the ones provided by Java. The notable one is org.apache.juli.FileHandler.

org.apache.juli.FileHandler  supports buffering of the logs. The buffering is not enabled by default. To configure it, use the bufferSize property of a handler. The value of 0 uses system default buffering (typically an 8K buffer will be used). A value of <0 forces a writer flush upon each log write. A value >0 uses a BufferedOutputStream with the defined value but note that the system default buffering will also be applied.

Example logging.properties  file to be placed in $CATALINA_BASE/conf:

 

Example logging.properties  for the servlet-examples web application to be placed in WEB-INF/classes inside the web application: