Logging in Tomcat

&project; Logging in Tomcat Allistair Crossley Yoav Shapira

Logging in Apache Tomcat is implemented with the help of Apache Commons Logging library. That library is a thin wrapper above different logging frameworks. It provides Tomcat with the ability to log hierarchically across various log levels without the need to rely on a particular logging implementation.

Since Tomcat 6.0, Tomcat uses a private package-renamed implementation of Apache Commons Logging, to allow web applications to use their own independent copies of the original Apache Commons Logging library. In the default distribution this private copy of the library is simplified and hardcoded to use the java.util.logging framework.

To configure Tomcat to use alternative logging frameworks for its internal logging, one has to replace the logging library with the one that is built with the full implementation. Such library is provided as an extras component. Instructions on how to configure Tomcat to use Log4j framework for its internal logging may be found below.

A web application running on Apache Tomcat can:

Use system logging API, java.util.logging.
Use the logging API provided by the Java Servlets specification, javax.servlet.ServletContext.log(...)
Use any logging framework of its choice.

The logging frameworks used by different web applications run independently of each other. See class loading for more details. The exception to this rule is java.util.logging, if it used directly or indirectly by your logging library. That is because it is loaded by the system and is shared across web applications.

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.

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

org.apache.catalina.core.ContainerBase.[${engine}].[${host}].[${context}]

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. The calls to ServletContext.log(String, Throwable) or GenericServlet.log(String, Throwable) are logged at the ERROR level.

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 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.

A related, but different feature is access logging. It can be configured as a valve at the Context, or Host, or Engine. See Valves documentation for more details.

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 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.

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:

org.apache.catalina.level=FINEST

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, 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. 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: 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, set the org.apache.catalina.util.LifecycleBase logger to log # each component that extends LifecycleBase changing state: #org.apache.catalina.util.LifecycleBase.level = FINE

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

See the following resources for additional information:

Apache Tomcat Javadoc for the org.apache.juli package.
Oracle Java 6 Javadoc for the java.util.logging package.

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 FileHandlers 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.

This section explains how to configure Tomcat to use log4j rather than java.util.logging for all Tomcat's internal logging.

Note: The steps described in this section are needed when you want to reconfigure Tomcat to use Apache log4j for its own logging. These steps are not needed if you just want to use log4j in your own web application. — In that case, just put log4j.jar and log4j.properties into WEB-INF/lib and WEB-INF/classes of your web application.

The following steps describe configuring log4j to output Tomcat's internal logging.

Create a file called log4j.properties with the following content and save it into $CATALINA_BASE/lib

log4j.rootLogger=INFO, CATALINA # Define all the appenders log4j.appender.CATALINA=org.apache.log4j.DailyRollingFileAppender log4j.appender.CATALINA.File=${catalina.base}/logs/catalina. log4j.appender.CATALINA.Append=true log4j.appender.CATALINA.Encoding=UTF-8 # Roll-over the log once per day log4j.appender.CATALINA.DatePattern='.'yyyy-MM-dd'.log' log4j.appender.CATALINA.layout = org.apache.log4j.PatternLayout log4j.appender.CATALINA.layout.ConversionPattern = %d [%t] %-5p %c- %m%n log4j.appender.LOCALHOST=org.apache.log4j.DailyRollingFileAppender log4j.appender.LOCALHOST.File=${catalina.base}/logs/localhost. log4j.appender.LOCALHOST.Append=true log4j.appender.LOCALHOST.Encoding=UTF-8 log4j.appender.LOCALHOST.DatePattern='.'yyyy-MM-dd'.log' log4j.appender.LOCALHOST.layout = org.apache.log4j.PatternLayout log4j.appender.LOCALHOST.layout.ConversionPattern = %d [%t] %-5p %c- %m%n log4j.appender.MANAGER=org.apache.log4j.DailyRollingFileAppender log4j.appender.MANAGER.File=${catalina.base}/logs/manager. log4j.appender.MANAGER.Append=true log4j.appender.MANAGER.Encoding=UTF-8 log4j.appender.MANAGER.DatePattern='.'yyyy-MM-dd'.log' log4j.appender.MANAGER.layout = org.apache.log4j.PatternLayout log4j.appender.MANAGER.layout.ConversionPattern = %d [%t] %-5p %c- %m%n log4j.appender.HOST-MANAGER=org.apache.log4j.DailyRollingFileAppender log4j.appender.HOST-MANAGER.File=${catalina.base}/logs/host-manager. log4j.appender.HOST-MANAGER.Append=true log4j.appender.HOST-MANAGER.Encoding=UTF-8 log4j.appender.HOST-MANAGER.DatePattern='.'yyyy-MM-dd'.log' log4j.appender.HOST-MANAGER.layout = org.apache.log4j.PatternLayout log4j.appender.HOST-MANAGER.layout.ConversionPattern = %d [%t] %-5p %c- %m%n log4j.appender.CONSOLE=org.apache.log4j.ConsoleAppender log4j.appender.CONSOLE.Encoding=UTF-8 log4j.appender.CONSOLE.layout = org.apache.log4j.PatternLayout log4j.appender.CONSOLE.layout.ConversionPattern = %d [%t] %-5p %c- %m%n # Configure which loggers log to which appenders log4j.logger.org.apache.catalina.core.ContainerBase.[Catalina].[localhost]=INFO, LOCALHOST log4j.logger.org.apache.catalina.core.ContainerBase.[Catalina].[localhost].[/manager]=\ INFO, MANAGER log4j.logger.org.apache.catalina.core.ContainerBase.[Catalina].[localhost].[/host-manager]=\ INFO, HOST-MANAGER

Download Log4J (v1.2 or later).
Download or build tomcat-juli.jar and tomcat-juli-adapters.jar that are available as an "extras" component for Tomcat. See Additional Components documentation for details.

This tomcat-juli.jar differs from the default one. It contains the full Apache Commons Logging implementation and thus is able to discover the presense of log4j and configure itself.
If you want to configure Tomcat to use log4j globally:
- Put log4j.jar and tomcat-juli-adapters.jar from "extras" into $CATALINA_HOME/lib.
- Replace $CATALINA_HOME/bin/tomcat-juli.jar with tomcat-juli.jar from "extras".
If you are running Tomcat with separate $CATALINA_HOME and $CATALINA_BASE and want to configure to use log4j in a single $CATALINA_BASE only:
- Create $CATALINA_BASE/bin and $CATALINA_BASE/lib directories if they do not exist.
- Put log4j.jar and tomcat-juli-adapters.jar from "extras" into $CATALINA_BASE/lib
- Put tomcat-juli.jar from "extras" as $CATALINA_BASE/bin/tomcat-juli.jar
- If you are running with a security manager, you would need to edit the $CATALINA_BASE/conf/catalina.policy file to adjust it to using a different copy of tomcat-juli.jar.
Delete $CATALINA_BASE/conf/logging.properties to prevent java.util.logging generating zero length log files.
Start Tomcat

This log4j configuration mirrors the default java.util.logging setup that ships with Tomcat: both the manager and host-manager apps get an individual log file, and everything else goes to the "catalina.log" log file. Each file is rolled-over once per day.

You can (and should) be more picky about which packages to include in the logging. Tomcat defines loggers by Engine and Host names. For example, for a more detailed Catalina localhost log, add this to the end of the log4j.properties above. Note that there are known issues with using this naming convention (with square brackets) in log4j XML based configuration files, so we recommend you use a properties file as described until a future version of log4j allows this convention.

log4j.logger.org.apache.catalina.core.ContainerBase.[Catalina].[localhost]=DEBUG
log4j.logger.org.apache.catalina.core=DEBUG
log4j.logger.org.apache.catalina.session=DEBUG

Be warned: a level of DEBUG will produce megabytes of logging and slow startup of Tomcat. This level should be used sparingly when debugging of internal Tomcat operations is required.

Your web applications should certainly use their own log4j configuration. This is valid with the above configuration. You would place a similar log4j.properties file in your web application's WEB-INF/classes directory, and log4jx.y.z.jar into WEB-INF/lib. Then specify your package level logging. This is a basic setup of log4j which does *not* require Commons-Logging, and you should consult the log4j documentation for more options. This page is intended only as a bootstrapping guide.

Additional notes

This exposes log4j libraries to the web applications through the Common classloader. See class loading documentation for details.

Because of that, the web applications and libraries using Apache Commons Logging library are likely to automatically choose log4j as the underlying logging implementation.
The java.util.logging API is still available, for those web applications that use it directly. The ${catalina.base}/conf/logging.properties file is still referenced by Tomcat startup scripts.

Removal of ${catalina.base}/conf/logging.properties file, mentioned as one of the steps, just causes java.util.logging to fallback to the default configuration as configured in JRE, which is to use a ConsoleHandler and do not create any files.