Effective Level aka Level Inheritance

Loggers may be assigned levels. The set of possible levels (TRACE, DEBUG, INFO, WARN and ERROR) are defined in the ch.qos.logback.classic.Level class. Note that in logback, the Level class is final and cannot be sub-classed, as a much more flexible approach exists in the form of Marker objects.

If a given logger is not assigned a level, then it inherits one from its closest ancestor with an assigned level. More formally:

The effective level for a given logger L, is equal to the first non-null level in its hierarchy, starting at _L _itself and proceeding upwards in the hierarchy towards the root logger.

To ensure that all loggers can eventually inherit a level, the root logger always has an assigned level. By default, this level is DEBUG.

Below are four examples with various assigned level values and the resulting effective (inherited) levels according to the level inheritance rule.

Example 1

In example 1 above, only the root logger is assigned a level. This level value, DEBUG, is inherited by the other loggers X, X.Y and X.Y.Z

Example 2

In example 2 above, all loggers have an assigned level value. Level inheritance does not come into play.

Example 3

In example 3 above, the loggers root, X and X.Y.Z are assigned the levels DEBUG, INFO and ERROR respectively. Logger X.Y inherits its level value from its parent X.

Example 4

In example 4 above, the loggers root and X and are assigned the levels DEBUG and INFO respectively. The loggers X.Y and X.Y.Z inherit their level value from their nearest parent X, which has an assigned level.