创建记录器Java时未调用构造函数

Question

I was implementing my Logger class but for a strange reason the constructor method is never called. In other class when I use SRCLogger.getLogger().log(Level.INFO, "Message"); there's no log-file created on the path.

What am I missing? What's wrong in this code?

Here's my code:

public final class SRCLogger implements Serializable{

    private static final Logger l = Logger.getLogger("mySRCLogger");
    private FileHandler fh;

    private String ROOT_DIR = "C:\\Users\\Test\\Desktop\\";

    public SRCLogger(){
        System.out.println("Constructor.");
        try {
            fh = new FileHandler(ROOT_DIR + "SRCLog.log");
            fh.setFormatter(new SimpleFormatter());
            l.addHandler(fh);
            System.out.println("Try.");
        } catch (IOException ex) {
            Logger.getLogger(SRCLogger.class.getName()).log(Level.SEVERE, null, ex);
            System.out.println("Catch IOException.");
        } catch (SecurityException ex) {
            Logger.getLogger(SRCLogger.class.getName()).log(Level.SEVERE, null, ex);
            System.out.println("Catch SecurityException.");
        }
    }

    public static Logger getLogger(){
        return l;
    }   
}

Cheers and thanks in advance

Answer 1

Quite simply - you're never calling the constructor. You're calling this:

public static Logger getLogger(){
    return l;
}

... which returns l , a static field initialized like this:

private static final Logger l = Logger.getLogger("mySRCLogger");

Why would you expect that to trigger your class to be instantiated? The fact that you don't have any instance methods is also a design smell - what are you expecting the class to accomplish, other than adding a handler to an existing logger? If that's all you want to do, I would change your class to just have a static method - you don't really need any instances as far as I can tell.

Answer 2

In order for the constructor to be called, the object has to be instantiated using the "new" keyword. If you call only the static methods of the class (not the object), the constructor will not be called.

So

   SRCLogger.getLogger() 

is a static method being called.

If you do something like

   new SRCLogger().getLogger()

, then the constructor will be called, but it is not good practice to call a static method on an object instance. Static methods ought to be called on the class itself.