Logger in Java
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Logging is the act of writing information about events in the application to a file, also called the log file.
Why do we need logging?
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1) Troubleshooting
2) Performance Analytics
3) Auditing - safety and traffic
Who will benefit?
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1) Software Developers
2) System Administrators
3) Support Team
When to use Logging?
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1) Exceptions and errors
2) Events and States
3) Debug info
4) HTTP requests - if our app uses an external API we might send the log request to it and the response we are getting.
5) Thread Usage - deadlock problem analysis
6) Frontend errors
Different Loggers Available/Logging Framework:-
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1) Very popular library: log4j
2) Since java 1.4: java.util.Logging
3) LogBack
4) Commons Logging
Log Levels:-
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Log levels represent the severity of the situation. There are 7 logging levels:-
1) SEVERE
2) WARNING
3) INFO
4) CONFIG
5) FINE
6) FINER
7) FINEST
Log Handlers:-
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1) Sends the message to the log place
2) Handlers format the message using a formatter.
3) Handlers intercept to log rockets and it processes them before they get set onto the log.
Types of Handlers:-
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1) ConsoleHandler - default Handler
2) FileHandler
3) StreamHandler
4) SocketHandler
5) MemoryHandler
Logging Best Practices:-
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1) Be precise
2) No Sensitive data
3) Right log level
4) Machine and human-readable
5) Don't log too much
6) Don't log too little
Different Log Methods:-
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1) LOGGER.log(Level.INFO, "This is an example message");
2) LOGGER.logp(Level.INFO, LogExample.class.getName(), "sourceMethodName", "This is an example message");
3) LOGGER.logrb(Level.INFO, ResourceBundle.getBundle("en_US"), "This is an example message");
Logging Filter:-
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Filter is an interface. The isLoggable method must be implemented. If it returns true for a certain log message, it will be sent to the handler and will be logged. If it returns false, it will be ignored.
Filter can be set on the logger.
LogManager:-
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1) The LogManager is the class responsible for managing the logging hierarchy.
2) It loads the configuration for all the loggers. This can be done through a special config class or a config file.
3) LogManager is a Singleton.
The Best Spring Data JPA Logging Configuration in Spring Boot:-
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Logging Configuration for Development:-
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# Generate and log statistics
spring.jpa.properties.hibernate.generate_statistics=true
logging.level.org.hibernate.stat=DEBUG
# Log slow queries
spring.jpa.properties.hibernate.session.events.log.LOG_QUERIES_SLOWER_THAN_MS=1
# Log all SQL statements
logging.level.org.hibernate.SQL=DEBUG
# Logging cache operations
logging.level.org.hibernate.cache=DEBUG
Logging Configuration for Production:-
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spring.jpa.properties.hibernate.generate_statistics=false
logging.level.org.hibernate=ERROR
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