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Logging in Tomcat
Table of Contents
- Introduction
- Using java.util.logging (default)
Introduction
Mar 06, 2021 As of Log4j 2.13.0 Log4j 2 requires Java 8 or greater at runtime. This release contains new features and fixes which can be found in the latest changes report. Log4j 2.14.0 contains a new Layout, JsonTemplateLayout, that is intended to ultimately replace JsonLayout. How to implement log rotation with Log4j on Tomcat 8 Created by user-1417c, last modified by Jordan M on Oct 24, 2019 The Lucee Installer does not come with ability to rotate logs built into it. Instead, the Lucee installers ship with Tomcat's default logging mechanism, java.util.logging.
Instead, the Lucee installers ship with Tomcat's default logging mechanism, java.util.logging. This is simple and effective logging that will work in most situations, but if you want more complex features, such as rotation based on date or size, you will need to upgrade Tomcat to use a more advanced logging mechanism, such as Log4j. Log4j - Logging in Database - The log4j API provides the org.apache.log4j.jdbc.JDBCAppender object, which can put logging information in a specified database.
The internal logging for Apache Tomcat uses JULI, a packaged renamed fork of Apache Commons Logging that is hard-coded to use the
java.util.logging
framework. This ensures that Tomcat's internal logging and any web application logging will remain independent, even if a web application uses Apache Commons Logging. To configure Tomcat to use an alternative logging framework for its internal logging, follow the instructions provided by the alternative logging framework for redirecting logging for applications that use
java.util.logging
. Keep in mind that the alternative logging framework will need to be capable of working in an environment where different loggers with the same name may exist in different class loaders. A web application running on Apache Tomcat can:
- Use any logging framework of its choice.
- Use system logging API,
java.util.logging
. - Use the logging API provided by the Java Servlets specification,
javax.servlet.ServletContext.log(..)
The logging frameworks used by different web applications are independent. See class loading for more details. The exception to this rule is
java.util.logging
. If it is used directly or indirectly by your logging library then elements of it will be shared across web applications because it is loaded by the system class loader. Java logging API — java.util.logging
Apache Tomcat has its own implementation of several key elements of
java.util.logging
API. This implementation is called JULI. The key component there is a custom LogManager implementation, that is aware of different web applications running on Tomcat (and their different class loaders). It supports private per-application logging configurations. It is also notified by Tomcat when a web application is unloaded from memory, so that the references to its classes can be cleared, preventing memory leaks. This
java.util.logging
implementation is enabled by providing certain system properties when starting Java. The Apache Tomcat startup scripts do this for you, but if you are using different tools to run Tomcat (such as jsvc, or running Tomcat from within an IDE), you should take care of them by yourself. More details about java.util.logging may be found in the documentation for your JDK and on its Javadoc pages for the
java.util.logging
package. More details about Tomcat JULI may be found below.
Servlets logging API
The calls to
javax.servlet.ServletContext.log(..)
to write log messages are handled by internal Tomcat logging. Such messages are logged to the category named This logging is performed according to the Tomcat logging configuration. You cannot overwrite it in a web application.
The Servlets logging API predates the
java.util.logging
API that is now provided by Java. As such, it does not offer you much options. E.g., you cannot control the log levels. It can be noted, though, that in Apache Tomcat implementation the calls to ServletContext.log(String)
or GenericServlet.log(String)
are logged at the INFO level. Frank turner songs. The calls to ServletContext.log(String, Throwable)
or GenericServlet.log(String, Throwable)
are logged at the SEVERE level. Console
When running Tomcat on unixes, the console output is usually redirected to the file named
catalina.out
. The name is configurable using an environment variable. (See the startup scripts). Whatever is written to System.err/out
will be caught into that file. That may include: - Uncaught exceptions printed by
java.lang.ThreadGroup.uncaughtException(.)
- Thread dumps, if you requested them via a system signal
When running as a service on Windows, the console output is also caught and redirected, but the file names are different.
The default logging configuration in Apache Tomcat writes the same messages to the console and to a log file. This is great when using Tomcat for development, but usually is not needed in production.
Old applications that still use
Note, that the
System.out
or System.err
can be tricked by setting swallowOutput
attribute on a Context. If the attribute is set to true
, the calls to System.out/err
during request processing will be intercepted, and their output will be fed to the logging subsystem using the javax.servlet.ServletContext.log(..)
calls.Note, that the
swallowOutput
feature is actually a trick, and it has its limitations. It works only with direct calls to System.out/err
, and only during request processing cycle. It may not work in other threads that might be created by the application. It cannot be used to intercept logging frameworks that themselves write to the system streams, as those start early and may obtain a direct reference to the streams before the redirection takes place. Access logging
Access logging is a related but different feature, which is implemented as a
Valve
. It uses self-contained logic to write its log files. The essential requirement for access logging is to handle a large continuous stream of data with low overhead, so it only uses Apache Commons Logging for its own debug messages. This implementation approach avoids additional overhead and potentially complex configuration. Please refer to the Valves documentation for more details on its configuration, including the various report formats. 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:
Apache Tomcat 8 Download
- Globally. That is usually done in the
${catalina.base}/conf/logging.properties
file. The file is specified by thejava.util.logging.config.file
System property which is set by the startup scripts. If it is not readable or is not configured, the default is to use the${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 AsyncFileHandler
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. 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.: 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: - 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
${systemPropertyName}
. - If using a class loader that implements the
org.apache.juli.WebappProperties
interface (Tomcat's web application class loader does) then property replacement is also performed for${classloader.webappName}
,${classloader.hostName}
and${classloader.serviceName}
which are replaced with the web application name, the host name and the service name respectively. - 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 ones are
org.apache.juli.FileHandler
and org.apache.juli.AsyncFileHandler
. 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. org.apache.juli.AsyncFileHandler
is a subclass of FileHandler
that queues the log messages and writes them asynchronously to the log files. Its additional behaviour can be configured by setting some system properties. 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: Winbox gns3.
Documentation references
Tomcat 8 Use Log4j
Christmas songs uke chords. See the following resources for additional information:
- Apache Tomcat Javadoc for the
org.apache.juli
package. - Oracle Java 7 Javadoc for the
java.util.logging
package.
Considerations for production usage
Tomcat 8 Log4j
You may want to take note of the following:
Tomcat 8.0 Download
- Consider removing
ConsoleHandler
from configuration. By default (thanks to the.handlers
setting) logging goes both to aFileHandler
and to aConsoleHandler
. The output of the latter one is usually captured into a file, such ascatalina.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 forhost-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.