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20080425 Friday April 25, 2008

NetBeans Lookup Example

Lookup example, producing a new message automatically every 2 seconds:

  • Provider module: 

    public final class Selection {

    private Selection() {
    }

    private static MyLookup LKP = new MyLookup();

    //Make the Lookup accessible:
    public static Lookup getSelection() {
        return LKP;
    }

    private static final class MyLookup extends ProxyLookup
            implements Runnable {

        private static ScheduledExecutorService EX = 
                Executors.newSingleThreadScheduledExecutor();

        public MyLookup() {
            EX.schedule(this, 2000, TimeUnit.MILLISECONDS);
        }

        private int i;

        @Override
        public void run() {
            //Add to the Lookup a new MyHello:
            setLookups(Lookups.singleton(new MyHello(i++)));
            EX.schedule(this, 2000, TimeUnit.MILLISECONDS);
        }

    }

    private static final class MyHello implements HelloProvider {

        private String text;

        public MyHello(int i) {
            text = i % 2 == 0 ? "Hello from Tom" : "Hello from Jerry";
        }

        public String sayHello() {
            return text;
        }

    }
    
}

    public interface HelloProvider {
    public String sayHello();
}

  • Consumer module, with dependency on the provider module: 

    final class HelloTopComponent extends TopComponent implements LookupListener {

    private static HelloTopComponent instance;
    private static final String PREFERRED_ID = "HelloTopComponent";
    private Result result;

    private HelloTopComponent() {
        
        ...
        ...
        ...

        //We have a dependency on the provider module,
        //where we can access Selection.getSelection():
        Lookup lookup = Selection.getSelection();

        //Get the HelloProvider from the result:
        result = lookup.lookupResult(HelloProvider.class);
        
        //Add LookupListener on the result:
        result.addLookupListener(this);

        //Call result changed:
        resultChanged(null);
        
    }

    StringBuilder sb = new StringBuilder();
    int i;

    @Override
    public void resultChanged(LookupEvent arg0) {
        long mills = System.currentTimeMillis();
        Collection instances = result.allInstances();
        for (HelloProvider helloProvider : instances) {
            String hello = helloProvider.sayHello();
            sb.append(mills + ": " + hello + "\n");
            jTextArea1.setText(sb.toString());
        }
    }

   ...
   ...
   ...

Result:

Apr 25 2008, 07:54:49 AM PDT Permalink

Trackback URL: http://blogs.sun.com/geertjan/entry/lookup_example
Comments:

Hi Geertjan,

at the moment I am really interested in things like servicelocator, dependency injection (DI) and the stuff, too. I only knew spring, but some days ago I discovered this container:
http://www.picocontainer.org
(and guice ...)

I like picocontainer, because it is quite small (<200 KB), there are a lot of interesting features and the authors are quite helpful. If you use nanocontainer.org on the top you can e.g. configure the container via xml, beanshell, groovy ...

And I have learned that a singleton could be an anti-pattern:
http://www.picocontainer.org/singleton-antipattern.html
They (from picocontainer) wouldn't use "Lookup Selection.getSelection()" they would use DI:

private HelloTopComponent(Lookup lookup){
...
}

But at the moment I don't know if the picocontainer API would provide sth. similar to the result.addLookupListener method. Maybe the start/stop methods there could help, I'll figure it out if you are interested.

If you would like to see my first (stupid) swing app you can visit:
http://timefinder.sourceforge.net/files/PicoExample-1.1.zip

To build it, just copy dist/lib/* to lib and use netbeans ;-)

Regards,
Peter.

PS: Keep on good posting ;-)

Posted by Peter on April 25, 2008 at 01:54 PM PDT #

xxx

Posted by 193.204.253.179 on April 28, 2008 at 08:44 AM PDT #

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