Log4j 面试题与答案

问题 26. What are the system properties checked by log4j?

The system properties checked by log4j are

• Log4j debug, if true, log4j will show internal debugging messages to the console
• defaultInitOverride, if true, log4j will not execute default initialization
• configuration, URL for default initialization configuration file
• configurationClass, Class name for configurator to execute default initialization configuration file
• ignoreTCL, if true, the thread class loader will be overlooked when loading classes

问题 27. What is the role of the filter in log4j?

Filter objects in log4j decide whether logging requests should be handled by a particular Appender or ignored.

问题 28. How can you get multiple processes to log into the same file?

You may have each process log to a socket Appender. The receiving socket server can receive all the events and send them to a single log file.

问题 29. What is the difference between Threshold and LevelRangeFilter in log4j?

Both Threshold and LevelRangeFilter do the same thing.

However, the threshold should be faster. Filters enable you to implement your own logic, and you can also link them together if required. If you need a basic threshold functionality, then the “threshold” function will be enough.

问题 30. Explain what does WARN and TRACE level indicates in log4j?

Log4j level WARN gives a warning about an unpredicted event to the user. The messages coming out of this level may not stop the progress of the system.

The TRACE level provides more detailed information than the DEBUG level, and it will stay at the top of the hierarchy.