log4j logging hierarchy order

Question

What is the hierarchy of log4j logging?

DEBUG
INFO
WARN
ERROR
FATAL

Which one provides the highest logging which would be helpful to troubl

Answer 1

Use the force, read the source (excerpt from the Priority and Level class compiled, TRACE level was introduced in version 1.2.12):

public final static int OFF_INT = Integer.MAX_VALUE;
public final static int FATAL_INT = 50000;
public final static int ERROR_INT = 40000;
public final static int WARN_INT  = 30000;
public final static int INFO_INT  = 20000;
public final static int DEBUG_INT = 10000;
public static final int TRACE_INT = 5000; 
public final static int ALL_INT = Integer.MIN_VALUE; 

or the log4j API for the Level class, which makes it quite clear.

When the library decides whether to print a certain statement or not, it computes the effective level of the responsible Logger object (based on configuration) and compares it with the LogEvent's level (depends on which method was used in the code – trace/debug/.../fatal). If LogEvent's level is greater or equal to the Logger's level, the LogEvent is sent to appender(s) – "printed". At the core, it all boils down to an integer comparison and this is where these constants come to action.