Log4j - Interview Questions and Answers for 'Log4j' | Search Interview Question

Log4j - Interview Questions and Answers for 'Log4j' - 21 question(s) found - Order By Newest

Q1. What are some different logging levels for log4j ?

Log4j

Ans. DEBUG
ERROR
ALL
WARN
INFO
FATAL
OFF
TRACE
TRACE_INT
WARN

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Q2. How will you design a Log4j kind of framework.

Log4j

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Q3. Difference between log4j and slf4j ?

Logging

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Q4. What is the difference between log4j and java logging api.

Log4j

Ans. log4j is by apache while java logging api is given by sun. log4j is more powerful,extensible and simple to use than java logging api.

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Q5. What is the difference between TimeBasedRollingPolicy and SizeBasedTriggeringPolicy within Log4j ? Can we use both together and What would that mean ?

Log4j

Ans. TimeBasedRollingPolicy enables rolling of logs based on the time / days whereas SizeBasedTriggeringPolicy enables rolling of logs based on size cap.

Yes we can use both together. In that case Logs will be rolled in case any of the condition is met i.e after the interval or if the size is reached.

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Q6. What is the difference between RollingFile and RollingRandomAccessFile in log4j ?

Log4j

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Q7. How can we change the Log level for the application ?

Log4j

Ans. By changing the Root Level within Log4j config.

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Q8. What is the default interval for TimeBasedTriggeringPolicy, if specified none like following

<Appenders>
<RollingFile name="RollingFile" fileName="logs/xyz.log" filePattern="logs/xyz-%d{MM-dd-yyyy}.log.gz"
ignoreExceptions="false">
<TimeBasedTriggeringPolicy />
</RollingFile>
</Appenders>

Log4j

Ans. 1 day

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Q9. In following log4j configuration file, How should we change the logging level to WARN

<Configuration status="DEBUG">
<Appenders>
<RollingFile name="File" fileName="logs/xyz.log" filePattern="logs/xyz-%d{MM-dd-yyyy}.log.gz">
<TimeBasedTriggeringPolicy />
</RollingFile>
</Appenders>
<Loggers>
<Root level="DEBUG">
<AppenderRef ref="File" />
</Root>
</Loggers>
</Configuration>

Log4j

Ans. We should change the root level from DEBUG to WARN

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Q10. in the following log4j config file, How should we change the file name and format

<Configuration status="DEBUG">
<Appenders>
<RollingFile name="File" fileName="logs/xyz.log" filePattern="logs/xyz-%d{MM-dd-yyyy}.log.gz">
<TimeBasedTriggeringPolicy />
</RollingFile>
</Appenders>
<Loggers>
<Root level="DEBUG">
<AppenderRef ref="File" />
</Root>
</Loggers>
</Configuration>

Log4j

Ans. We can specify the file name with fileName property within RollingFile. File name pattern for the rolled logs can be specified using filePattern property.

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Q11. In the following log4j config, What if we don't need rolling logs

<Configuration status="DEBUG">
<Appenders>
<RollingFile name="File" fileName="logs/xyz.log" filePattern="logs/xyz-%d{MM-dd-yyyy}.log.gz">
<TimeBasedTriggeringPolicy />
</RollingFile>
</Appenders>
<Loggers>
<Root level="DEBUG">
<AppenderRef ref="File" />
</Root>
</Loggers>
</Configuration>

Log4j

Ans. We can change the appender from RollingFile to File or we can specify a new File appender and set that within AppenderRef

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Q12. What are some of the Log4j appenders ?

Log4j

Ans. https://logging.apache.org/log4j/2.x/manual/appenders.html

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Q13. Can you organize following Log4j levels in hierarchy ?

WARN, DEBUG,INFO, ERROR

Log4j

Ans. DEBUG
INFO
WARN
ERROR

Root Log level of DEBUG will print all
Root Log Level of INFO will print INFO, WARN and ERROR
Root Log level of WARN will print WARN and ERROR
Root Log level of ERROR will print ERROR alone

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Q14. What are the application Logging levels specified in your applications ?

Log4j

Ans. In our Organization, the policy is to keep it WARN in production so as to reduce logging Noise. We use Info in Test environments.

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Q15. What should be the logging level while logging exceptions ?

Log4j

Ans. It depends on how severe the exception is. If the exception is completely unexpected and breaks the request, It should be logged as ERROR or FATAL. If it's not expected but we can live with it and the application request continue in-spite of it, It should be WARN. If it's expected , it can be just INFO.

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Q16. What is the difference between INFO and DEBUG logging levels ?

Log4j

Ans. Info Messages are something which we would like to see even if the application is in best of state. DEBUG messages are usually something that we would like to see while debugging some problem. DEBUG is lower level than Info. Any message logged with info gets printed if the Root level set is DEBUG.

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Q17. What is the difference between DEBUG and TRACE logging levels ?

Log4j

Ans. TRACE designates finer grained informational events than the DEBUG.TRACE is level lower than DEBUG.

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Q18. How to change the backup log directory using log4j ?

Log4j

Ans. There is a property called "filePattern" within appender that regulates where the backed up files will be created for rolling logs. It actually contains the absolute path which can be modified to have backed up logs within some other directory.

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Q19. What does the property maxBackupIndex in Log4j means ?

Log4j

Ans. It means that the app will only maintain these many backed up log files. Older backed up logs will be deleted.

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Q20. How can we switch log4j to print logging on console / file ?

Log4j

Ans. By changing ConsoleAppender to a FileAppender and vice versa

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Q21. Have you ever done audit logging using log4j ?

Log4j

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