Question

Need: Output a Java application’s log into a GUI component, such as a JTextArea.

Concern: Need to log things from any class, in a static manner. However, the GUI logger component must not be static (obviously) as it’s the member of a parent component.

What should I do?

Answer 1

Create a singelton log provider and add the “textfield” as a listener to it.

Example of the logger singelton:

interface Listener {
    void log(String log);
}

enum Logger {

    instance;

    private List<Listener> listeners = new LinkedList<Listener>();

    public void addListener(Listener l) {
    synchronized(listeners) {
        listeners.add(l);
     }
    }

    public void log(String log) {
        synchronized(listeners) {
            for(Listener l : listeners)
                l.log(log);
        }
    }
}

Add your listener (which you will need to implement yourself) like this:

Logger.instance.addListener(myTextField);

And use it (from any class) like this:

Logger.instance.log("Hello World!");

Or you can use a package like log4j.