The default implementation of java.util.logging provided in the JDK is too limited to be useful. A limitation of JDK Logging appears to be 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. It 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 slightly 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:
- 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. - 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 FileHandler
s 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.
Here is how you would set debugging from Tomcat. You would need to ensure the ConsoleHandler's (or FileHandler's') level is also set to collect this threshold, so FINEST or ALL should be set. Please refer to java.util.logging
documentation in the JDK for the complete details:
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 | org.apache.catalina.level=FINEST |  |
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The configuration used by JULI is extremely similar to the one supported by plain java.util.logging
, but uses a few extensions to allow better flexibility in assigning loggers. The main differences are:
- 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. - System property replacement is performed for property values which contain ${systemPropertyName}.
- As in Java 6.0, loggers can define a list of handlers using the
loggerName.handlers
property. - 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.
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. A 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:
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 | handlers = 1catalina.org.apache.juli.FileHandler, \
2localhost.org.apache.juli.FileHandler, \
3manager.org.apache.juli.FileHandler, \
java.util.logging.ConsoleHandler
.handlers = 1catalina.org.apache.juli.FileHandler, java.util.logging.ConsoleHandler
############################################################
# Handler specific properties.
# Describes specific configuration info for Handlers.
############################################################
1catalina.org.apache.juli.FileHandler.level = FINE
1catalina.org.apache.juli.FileHandler.directory = ${catalina.base}/logs
1catalina.org.apache.juli.FileHandler.prefix = catalina.
2localhost.org.apache.juli.FileHandler.level = FINE
2localhost.org.apache.juli.FileHandler.directory = ${catalina.base}/logs
2localhost.org.apache.juli.FileHandler.prefix = localhost.
3manager.org.apache.juli.FileHandler.level = FINE
3manager.org.apache.juli.FileHandler.directory = ${catalina.base}/logs
3manager.org.apache.juli.FileHandler.prefix = manager.
3manager.org.apache.juli.FileHandler.bufferSize = 16384
java.util.logging.ConsoleHandler.level = FINE
java.util.logging.ConsoleHandler.formatter = java.util.logging.SimpleFormatter
############################################################
# Facility specific properties.
# Provides extra control for each logger.
############################################################
org.apache.catalina.core.ContainerBase.[Catalina].[localhost].level = INFO
org.apache.catalina.core.ContainerBase.[Catalina].[localhost].handlers = \
2localhost.org.apache.juli.FileHandler
org.apache.catalina.core.ContainerBase.[Catalina].[localhost].[/manager].level = INFO
org.apache.catalina.core.ContainerBase.[Catalina].[localhost].[/manager].handlers = \
3manager.org.apache.juli.FileHandler
# For example, to log debug messages in ContextConfig and HostConfig
# classes and to log only warnings and errors in other
# org.apache.catalina.** classes, uncomment these lines:
#org.apache.catalina.startup.ContextConfig.level = FINE
#org.apache.catalina.startup.HostConfig.level = FINE
#org.apache.catalina.level = WARNING
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Example logging.properties for the servlet-examples web application to be placed in WEB-INF/classes inside the web application:
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 | handlers = org.apache.juli.FileHandler, java.util.logging.ConsoleHandler
############################################################
# Handler specific properties.
# Describes specific configuration info for Handlers.
############################################################
org.apache.juli.FileHandler.level = FINE
org.apache.juli.FileHandler.directory = ${catalina.base}/logs
org.apache.juli.FileHandler.prefix = servlet-examples.
java.util.logging.ConsoleHandler.level = FINE
java.util.logging.ConsoleHandler.formatter = java.util.logging.SimpleFormatter
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Considerations for productive usage |
You may want to take note of the following:
-
Consider removing ConsoleHandler from configuration. By default (thanks to the .handlers setting) logging goes both to a FileHandler and to a ConsoleHandler . The output of the latter one is usually captured into a file, such as catalina.out . Thus you end up with two copies of the same messages. -
Consider removing FileHandler s for the applications that you do not use. E.g., the one for host-manager . -
The handlers by default use the system default encoding to write the log files. It can be configured with encoding property. See Javadoc for details. -
Consider configuring an Access log.
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