21 December 2020

#Log4j

#Log4j

Key Concepts


Topic SubTopic Basic ✅ Intermediate ✅ Advanced ✅ Expert ✅
Introduction What is Log4j, Features, Benefits, Logging levels ✅ ✅ ✅ ✅
Installation & Setup Dependencies, Configuration files, Log4j2.xml, Classpath setup ✅ ✅ ✅ ✅
Loggers Logger hierarchy, Root logger, Named logger, Logger levels ✅ ✅ ✅ ✅
Appenders Console, File, RollingFile, Socket, SMTP, Custom Appenders ✅ ✅ ✅ ✅
Layouts PatternLayout, HTMLLayout, JSONLayout, Custom layouts ✅ ✅ ✅ ✅
Filters LevelRangeFilter, ThresholdFilter, Custom filters ✅ ✅ ✅ ✅
Configuration XML, Properties, YAML, JSON configuration, Programmatic config ✅ ✅ ✅ ✅
Asynchronous Logging AsyncAppender, Thread safety, Performance benefits ✅ ✅ ✅
Logging Performance Buffering, Async logging, Garbage collection impact ✅ ✅ ✅
Advanced Features Custom appenders, Custom filters, MDC/NDC, Lookups ✅ ✅
Error Handling Handling exceptions in logging, Failover strategies ✅ ✅ ✅
Integration Spring Boot, SLF4J, Logback bridge, Application frameworks ✅ ✅ ✅
Monitoring & Maintenance Log rotation, Archiving, Log cleanup, Metrics ✅ ✅ ✅
Security Masking sensitive data, Secure logging, Audit logs ✅ ✅ ✅
Best Practices Structured logging, Correlation IDs, Logging guidelines ✅ ✅ ✅ ✅

Interview question

1. Introduction ? What is Log4j, Features, Benefits, Logging levels

  1. What is Log4j?
  2. Explain the main features of Log4j.
  3. What are the benefits of using Log4j?
  4. List the logging levels in Log4j.
  5. What is the difference between DEBUG and INFO levels?
  6. What is the difference between WARN and ERROR levels?
  7. How does Log4j help in application debugging?
  8. Can you disable logging in production? How?
  9. What are common use cases for Log4j?
  10. How does Log4j differ from System.out.println logging?

2. Installation & Setup ? Dependencies, Configuration files, Classpath

  1. How do you install Log4j in a Java project?
  2. What are the required dependencies for Log4j2?
  3. What is the default configuration file name for Log4j2?
  4. How to configure Log4j using XML?
  5. How to configure Log4j using Properties file?
  6. How to configure Log4j using JSON or YAML?
  7. How to set the classpath for Log4j configuration?
  8. Can you programmatically configure Log4j? How?
  9. What are common configuration mistakes?
  10. How to verify that Log4j is initialized correctly?

3. Loggers ? Logger hierarchy, Root logger, Named logger, Logger levels

  1. What is a Logger in Log4j?
  2. Explain Logger hierarchy in Log4j.
  3. What is the root logger?
  4. How to create a named logger?
  5. How to set different levels for different loggers?
  6. What is additive behavior in loggers?
  7. How to prevent logger messages from propagating?
  8. Can loggers be defined programmatically?
  9. Difference between Logger and Root Logger?
  10. How to log messages to multiple loggers?

4. Appenders ? Console, File, RollingFile, Socket, SMTP, Custom

  1. What is an Appender in Log4j?
  2. How to configure ConsoleAppender?
  3. How to configure FileAppender?
  4. What is RollingFileAppender and why use it?
  5. How to configure SMTPAppender for email notifications?
  6. How to configure SocketAppender for remote logging?
  7. How to create a custom Appender?
  8. Difference between FileAppender and RollingFileAppender?
  9. How does AsyncAppender work?
  10. What are best practices for choosing appenders?

5. Layouts ? PatternLayout, HTMLLayout, JSONLayout, Custom layouts

  1. What is a Layout in Log4j?
  2. Explain PatternLayout and its placeholders.
  3. How to use HTMLLayout for logging?
  4. How to log in JSON format?
  5. How to create a custom layout?
  6. What is the default layout in Log4j?
  7. How to include timestamp and thread in log pattern?
  8. How to include MDC or NDC values in layout?
  9. Difference between HTMLLayout and PatternLayout?
  10. How to format logs for readability?

6. Filters ? LevelRangeFilter, ThresholdFilter, Custom filters

  1. What is a Filter in Log4j?
  2. How to use LevelRangeFilter?
  3. How to use ThresholdFilter?
  4. How to combine multiple filters?
  5. How to create a custom filter?
  6. Difference between Filter and Appender threshold?
  7. How to filter logs by logger name?
  8. How to filter logs by message content?
  9. Can filters be applied programmatically?
  10. Best practices for using filters?

7. Asynchronous Logging ? AsyncAppender, Thread safety, Performance

  1. What is AsyncAppender in Log4j?
  2. How does asynchronous logging improve performance?
  3. How to configure AsyncAppender?
  4. How to ensure thread safety with AsyncAppender?
  5. Difference between synchronous and asynchronous logging?
  6. How does Log4j handle high-volume logging?
  7. Can AsyncAppender work with multiple appenders?
  8. What is the internal queue in AsyncAppender?
  9. How to monitor dropped log events?
  10. Best practices for async logging?

8. Error Handling ? Handling exceptions in logging, Failover strategies

  1. How does Log4j handle errors during logging?
  2. What happens if a log file is not writable?
  3. How to configure failover appenders?
  4. How to prevent logging from crashing the application?
  5. How to handle exceptions inside custom appenders?
  6. Difference between FailoverAppender and BackupAppender?
  7. How to monitor logging errors?
  8. How to log errors without infinite loops?
  9. How to use ErrorHandler interface?
  10. Best practices for logging failures?

9. Integration ? Spring Boot, SLF4J, Logback bridge, Application frameworks

  1. How to integrate Log4j with Spring Boot?
  2. Difference between Log4j, SLF4J, and Logback?
  3. How to use Log4j through SLF4J?
  4. How to replace Logback with Log4j in Spring Boot?
  5. How to configure logging profiles in Spring Boot?
  6. How to log messages from third-party libraries?
  7. How to bridge java.util.logging to Log4j?
  8. How to integrate Log4j with web applications?
  9. How to log asynchronous processes in frameworks?
  10. How to use MDC/NDC in application frameworks?

10. Best Practices & Advanced Topics ? Structured logging, MDC, Security

  1. What is structured logging?
  2. How to use MDC (Mapped Diagnostic Context)?
  3. How to use NDC (Nested Diagnostic Context)?
  4. How to mask sensitive information in logs?
  5. How to implement correlation IDs for distributed tracing?
  6. Best practices for log file rotation and retention?
  7. How to monitor logs in production?
  8. How to analyze logs efficiently?
  9. How to secure log files?
  10. Advanced configuration tips for large-scale applications?

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