Developers use logs to understand what is happening in their applications. Logs can be used for debugging, monitoring, and auditing. They are also useful for troubleshooting production issues.
Logs are generated by the application at runtime. They can be written to a file, database, or both. Logging frameworks make it easy to add logging to an application.
There are different types of logs. Application logs contain information about the application itself. System logs contain information about the operating system and hardware. Access logs contain information about who is accessing the application and what they are doing.
Debugging is the process of finding and fixing errors in software. Logs can be used to debug software by providing information about what is happening in the application at runtime.
Debugging logs should be verbose. They should contain information about every step that is being executed. This information can be used to track down errors.
Monitoring is the process of tracking the performance of an application. Logs can be used to monitor applications by providing information about the resources that are being used.
Monitoring logs should be less verbose than debugging logs. They should contain information about the resources that are being used and how they are being used. This information can be used to track the performance of the application.
Auditing is the process of tracking the activity in an application. Logs can be used to audit applications by providing information about the actions that are being taken.
Auditing logs should be less verbose than monitoring logs. They should contain information about the actions that are being taken. This information can be used to track the activity in the application.
Troubleshooting is the process of finding and fixing problems in production. Logs can be used to troubleshoot production issues by providing information about what is happening in the application at runtime.
Troubleshooting logs should be less verbose than debugging logs. They should contain information about the resources that are being used and how they are being used. This information can be used to track down production issues.
Log levels are used to control the amount of information that is logged. They can be used to increase or decrease the verbosity of the logs.
There are six log levels:
Trace is the most verbose log level. Fatal is the least verbose log level.
The following is an example of how to use the logging framework log4j to write a debug log:
import org.apache.log4j.Logger;
public class MyClass {
private static final Logger logger = Logger.getLogger(MyClass.class);
public void myMethod() {
// log a debug message
logger.debug("This is a debug message");
}
}