Apache Log4j is a versatile, industrial-grade Java logging framework composed of an API, its implementation, and components to assist the deployment for various use cases. The project is actively maintained by a team of volunteers and supported by a big community. Log4j bundles a rich set of components to assist various use cases. Appenders targeting files, network sockets, databases, SMTP servers, etc. Layouts that can render CSV, HTML, JSON, Syslog, etc. formatted outputs. Filters based on log event rates, regular expressions, scripts, time, etc. Lookups for accessing system properties, environment variables, log event fields, etc. Log4j is built with solid reliability in mind. It can automatically reload its configuration upon modification and will do so without losing log events while reconfiguration occurs. When configured correctly, Log4j can deliver excelling performance without almost any burden on the Java garbage collector, and it will do so without sacrificing reliability.