All components of Saros are using the log4j2 framework as logging backend. Since Saros is an IDE plugin, the log dir depends on the IDEs configurations.

Initializing log4j2

Therefore, initializing the logging in Saros comprises the steps:

  1. The default log4j2 initializing is executed that uses the configuration file log4j2.xml (has to be included in the classpath).
  2. Our custom initializing starts:
    • We determine the IDEs log directory and the required log level (e.g. all if Saros is running the debug-mode).
    • We set the main arguments logLevel and logDir.
    • We force log4j to reinitialize with the log configuration saros_log4j2.xml that uses the defined arguments ( with the format main:<argument>).

See the initializing in the classes Saros (in Eclipse) or SarosComponent (in IntelliJ) for example implementations. Sometimes (as in the Saros Server) using the default initializing is enough.

Ongoing migration from log4j-1.2 -> log4j2

In most cases, migrating to log4j2 and only requires to change the used logger (see here for more details): org.apache.log4j.Logger.getLogger() -> org.apache.logging.log4j.LogManager.getLogger()

However, beside the required (minimal) migration step we should adopt the new functionality of log4j2 that allow us to avoid log level checks.

Avoid log level checks

With log4j2 supporting format string evaluation and (with Java 8) closure evaluation, we can migrate logging statements as:

if (log.isTraceEnabled())
  "id: "
  + namespaceId
  + " , namespace: "
  + namespace);

to a format string

log.trace("id: {}, namespace: {}", namespaceId, namespace)

or also a format string using a closure:

log.trace("id: {}, namespace: {}", () -> calculateId(), namespace)


In order to migrate from log4j-1.2 to log4j2 step-by-step we use the additional project dependency log4j2-1.2-api that routes all log4j-1.2 calls to log4j2. As soon as we migrated all these calls, we can remove this dependency and this migration documentation.