Dynamically Changing log4j log level

JMX / Spring: Dynamic log level changes

Running an application in Java/J2EE, you might not want to stop the server just to tweak log4j.xml. That's where JMX (Java Management Extensions) shines, exposing loggers to JMX consoles like JConsole, and enabling on-the-fly log level alterations without server restarts.

Spring applications can benefit from this, as loggers can be exposed through @ManagedResource and @ManagedAttribute. The /loggers endpoint of Spring Boot Actuator is another good friend in this journey.

Thread-safe log level updates: configureAndWatch concerns

Log4j 1.x's configureAndWatch looks enticing due to its automatic reconfiguration capability, but beware of potential thread leaks in J2EE environments — it starts a new thread that the application server might not handle well. Log4j 2 tried to simplify things with its monitorInterval attribute in log4j2.xml.

Manipulating log levels programmatically with Log4j 2

In Log4j 2, we flex some more muscles with the Configurator class:

import org.apache.logging.log4j.core.config.Configurator;
import org.apache.logging.log4j.Level;

Configurator.setAllLevels(LogManager.getRootLogger().getName(), Level.INFO);
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Here, monitorInterval in log4j2.xml could be your crucial tool to make sure your configuration is always up-to-date:

<Configuration monitorInterval="30">
  <!-- Rest of your configuration ensues. -->
</Configuration>
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This monitorInterval specifies the interval in seconds to check for configuration updates. Real neat trick!

Performance vs. Logging: Finding the sweet spot

The log level sensitivity you choose has a say in your application performance. DEBUG level verbosity might bog down your application speed and spike resource usage. So, be sure to weigh between your need for scrutinized logging and system performance, especially within production environments.

Also, remember, verbose logs require more storage space and may slow down log monitoring platforms. Always try to find the sweet spot that ensures effective debugging and cost optimization.

Maven & Dependencies: Necessary add-ons

For a Maven project, ensure pom.xml includes the correct log4j dependencies. For web applications, log4j-web might be needed to gel better with Servlet containers:

<dependency>
  <groupId>org.apache.logging.log4j</groupId>
  <artifactId>log4j-core</artifactId>
  <version>2.x.x</version> <!-- Always go for the latest version -->
</dependency>
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Specific versions can harmonize with your application server or servlet container, like Tomcat. If an IDE is your workplace, sync your project post dependencies addition or updating.

Various environments: Logging made easy

The need to manage logging varies across deployment scenarios:

• Tomcat: Look to conf/logging.properties
• Spring Boot: application.properties or application.yml will help you set up logging
• Docker Containers: Pass environment variables or bind mount custom configuration files

To avoid surprises, always test logging configurations in an environment closely resembling production.