Logging

Every Java programmer is familiar with the process of inserting calls to System.out.println into troublesome code to gain insight into program behavior. Of course, once you have figured out the cause of trouble, you remove the print statements, only to put them back in when the next problem surfaces. The logging API is designed to overcome this problem. Here are the principal advantages of the API:

• It is easy to suppress all log records or just those below a certain level, and just as easy to turn them back on.

• Suppressed logs are very cheap, so that there is only a minimal penalty for leaving the logging code in your application.

• Log records can be directed to different handlers, for display in the console, for storage in a file, and so on.

• Both loggers and handlers can filter records. Filters discard boring log entries, using any criteria supplied by the filter implementor.

• Log records can be formatted in different ways, for example, in plain text or XML.

• Applications can use multiple loggers, with hierarchical names such as com.mycompany.myapp, similar to package names.

• By default, the logging configuration is controlled by a configuration file. Applications can replace this mechanism if desired.