The Apache Tomcat 5.5 Servlet/JSP Container

Logging in Tomcat

Tomcat 5.5 uses Commons Logging throughout its internal code allowing the developer to choose a logging configuration that suits their needs, e.g java.util.logging or Log4J. Commons Logging provides Tomcat the ability to log hierarchically across various log levels without needing to rely on a particular logging implementation.

An important consequence for Tomcat 5.5 is that the <Logger> element found in previous versions to create a localhost_log is no longer a valid nested element of <Context>. Instead, the default Tomcat configuration will use java.util.logging. If the developer wishes to collect detailed internal Tomcat logging (i.e what is happening within the Tomcat engine), then they should configure a logging system such as java.util.logging or log4j as detailed next.

Tomcat 5.5 has done away with localhost_log which you may be familiar with as the runtime exception/stack trace log. These types of error are usually thrown by uncaught exceptions, but are still valuable to the developer. They can now be found in the stdout log.

If you need to setup cross-context detailed logging from within Tomcat's code, then you can use a simple log4j configuration. Note that this logging can be very verbose depending on the log level you chose to use. Note also that a log4j logging configuration is not going to produce stack trace type logging: those stack traces are output to stdout as discussed above.

Follow the following steps to setup a file named tomcat.log that has internal Tomcat logging output to it:

1. Create a file called log4j.properties with the following content and save it into common/classes.

   	log4j.rootLogger=DEBUG, R log4j.appender.R=org.apache.log4j.RollingFileAppender log4j.appender.R.File=${catalina.home}/logs/tomcat.log log4j.appender.R.MaxFileSize=10MB log4j.appender.R.MaxBackupIndex=10 log4j.appender.R.layout=org.apache.log4j.PatternLayout log4j.appender.R.layout.ConversionPattern=%p %t %c - %m%n

2. Download Log4J (v1.2 or later) and place the log4j jar in $CATALINA_HOME/common/lib.
3. Download Commons Logging and place the commons-logging-x.y.z.jar (not commons-logging-api-x.y.z.jar) in $CATALINA_HOME/common/lib with the log4j jar.
4. Start Tomcat

This log4j configuration sets up a file called tomcat.log in your Tomcat logs folder with a maximum file size of 10MB and up to 10 backups. DEBUG level is specified which will result in the most verbose output from Tomcat.

You can (and should) be more picky about which packages to include in the logging. Tomcat 5.5 uses defines loggers by Engine and Host names. For example, for a default 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, R
• log4j.logger.org.apache.catalina.core=DEBUG, R
• log4j.logger.org.apache.catalina.session=DEBUG, R

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 folder, and log4j1.2.8.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.

In order to configure JDK logging you should have JDK 1.4+. Tomcat 5.5 is intended for JDK 5.0 or later, but can be run on JDK 1.4 using a compatibility package.

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 in Tomcat 5.5, 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:

• In the JDK's logging.properties file. Check your JAVA_HOME environment setting to see which JDK Tomcat is using (or maybe JRE 5.0 as Tomcat can now run on a JRE from version 5.5). The file will be in $JAVA_HOME/jre/lib. Alternately, it can also use a global configuration file located elsewhere by using the system property java.util.logging.config.file, or programmatic configuration using java.util.logging.config.class.
• In each classloader using a logging.properties file. This means that it is possible to have a configuration for the Tomcat core, as well as separate configurations for each webapps which will have the same lifecycle as the webapps.

The default logging.properties specifies a ConsoleHandler for routing logging to stdout and also a FileHandler. A handler's log level threshold can be set using SEVERE, WARNING, INFO, CONFIG, FINE, FINER, FINEST or ALL. The logging.properties shipped with JDK is set to INFO. 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 level is also set to collect this threshold, so FINEST or ALL should be set. Please refer to Sun's java.util.logging documentation for the complete details.

	org.apache.catalina.level=FINEST

The configuration used by JULI is extremely similar, 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.
• As in Java 5.0, 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 a .handlers property.
• System property replacement for property values which start with ${sytstemPropertyName}.

Example logging.properties file to be placed in common/classes:

	handlers = 1catalina.org.apache.juli.FileHandler, 2localhost.org.apache.juli.FileHandler, \ 3manager.org.apache.juli.FileHandler, 4admin.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. 4admin.org.apache.juli.FileHandler.level = FINE 4admin.org.apache.juli.FileHandler.directory = ${catalina.base}/logs 4admin.org.apache.juli.FileHandler.prefix = admin. 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 org.apache.catalina.core.ContainerBase.[Catalina].[localhost].[/admin].level = INFO org.apache.catalina.core.ContainerBase.[Catalina].[localhost].[/admin].handlers = \ 4admin.org.apache.juli.FileHandler # For example, set the com.xyz.foo logger to only log SEVERE # messages: #org.apache.catalina.startup.ContextConfig.level = FINE #org.apache.catalina.startup.HostConfig.level = FINE #org.apache.catalina.session.ManagerBase.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

Tomcat's JULI implementation is not intended to be a fully-featured logging library, only a simple bridge to those libraries. However, JULI does provide several properties for configuring the its handlers. These are listed below.

FileHandler

Attribute Description directory The directory where the log file will be written. The Tomcat server account should have write permissions to this directory. The default value of this property is logs. prefix The log file name prefix. This is the portion of the log file name before the date. The default value of this property is juli.. suffix The log file name suffix. This is the portion of the log file name after the date. The default value of this property is .log. level The threshold level for this handler. It must be one of the levels in the java.util.logging.Level class. The default value of this property is ALL. Messages whose level is below the specified level will not be written to the file. filter The fully-qualified class name of a class that implements the java.util.logging.Filter interface. JULI will load this class and associate it with this handler to filter its messages. By default, there is no Filter associated with the handler. formatter The fully-qualified class name of a class that implements the java.util.logging.Formatter interface. JULI will load this class and associate it with this handler to format its messages. By default, there is no Formatter associated with the handler.