Question

From java.util.logging.Logger:

Logger names can be arbitrary strings, but they should normally be based on the package name or class name of the logged component, such as java.net or javax.swing

Could anyone explain this sentence to me ?

Answer 1

Logger names can be arbitrary strings, but they should normally be based on the package name or class name of the logged component, such as java.net or javax.swing”

“Logger names can be arbitrary strings …”:

public class Foo {
    private static final Logger logger = Logger.getLogger("specify logger name here - you can use any logger name you want, even supercalifragilisticexpialidocious");
}

Any code that wants the same logger instance just has to specify the same logger name (good luck spelling “supercalifragilisticexpialidocious” the same way twice).

However, you might want to share loggers more easily, get a handle to a specific class’ logger for configuration, or have a hierachical relationship between loggers (e.g. organize loggers to into parents and children). Classes and packages are already organized hierarchically, so they recommend that logger names:

“… should normally be based on the package name or class name of the logged component …”

package com.example.stackoverflow;

public class Foo {
    private static final Logger logger = Logger.getLogger("com.example.stackoverflow.Foo");
}

Now I can easily get a handle to any logger for any class from anywhere (I just need to know its fully qualified class name). Also, now the the Logger framework can see which loggers are related to which, e.g. that the logger for “com.example.stackoverflow” is the parent of the logger for “com.example.stackoverflow.Foo”.

But what if the package name changes or your class name changes? This code below does exactly the same thing as the code above, but in a less redundant and more maintainable manner:

package com.example.stackoverflow;

public class Foo {
    private static final Logger logger = Logger.getLogger(Foo.class.getName());
}

Now if the package changes, the logger name is handled automatically. If the class is renamed in an IDE, the IDE will likely notice the Foo.class literal in the getLogger call above and update the Foo.class literal accordingly.