SwingWorker in another SwingWorker’s done method

SwingWorker supports PropertyChange events, that is, you can listener to when the SwingWorker changes state or updates it’s progress…yes, SwingWorker even supports progress notification, for example

This means you could set up a PropertyChangeListener to monitor changes to the progress and state properties and take appropriate actions…

A worker that simple sets progress updates…

public class LoadMaster extends SwingWorker<Void, Progress> {

    @Override
    protected Void doInBackground() throws Exception {
        System.out.println("Working hard here, nothing to see...");
        for (int index = 0; index < 100; index++) {
            Thread.sleep(10);
            setProgress(index);
        }
        return null;
    }

    @Override
    protected void done() {
        try {
            get();
        } catch (Exception e) {
        }
    }

}

A example PropertyChangeListener…

public class LoadMasterPropertyChanegHandler implements PropertyChangeListener {

    private SwingWorkerExample example;

    public LoadMasterPropertyChanegHandler(SwingWorkerExample example) {
        this.example = example;
    }

    @Override
    public void propertyChange(PropertyChangeEvent evt) {
        System.out.println(evt.getPropertyName());
        if ("progress".equalsIgnoreCase(evt.getPropertyName())) {
            int value = (int) evt.getNewValue();
            example.showProgress(value);
        } else if ("state".equalsIgnoreCase(evt.getPropertyName())) {
            SwingWorker worker = (SwingWorker) evt.getSource();
            if (worker.isDone()) {
                try {
                    worker.get();
                    example.loadCompleted();
                } catch (InterruptedException | ExecutionException exp) {
                    example.loadFailed();
                }
            }
        }
    }

}

Now, all this does is sends back information to the SwingWorkerExample (it’s coming) which allows it to determine what it should do…

In this example, the loadCompleted method updates the UI and then starts the second worker…

protected void loadCompleted() {
    //...
    LoadStuffWorker stuffWorker = new LoadStuffWorker(this);
    stuffWorker.execute();
}

In all truth, I might use interfaces instead, so I’m not overtly exposing the class, but that’s a topic for another day…

And the full example…

import java.awt.EventQueue;
import java.awt.GridBagLayout;
import java.awt.GridLayout;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import java.util.concurrent.ExecutionException;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JProgressBar;
import javax.swing.SwingWorker;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.border.EmptyBorder;

public class SwingWorkerExample {

    private JProgressBar pb;
    private JPanel content;

    public static void main(String[] args) {

        new SwingWorkerExample();

    }

    public SwingWorkerExample() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                }

                pb = new JProgressBar();
                content = new JPanel();
                content.setBorder(new EmptyBorder(10, 10, 10, 10));

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setContentPane(content);
                frame.setLayout(new GridBagLayout());
                frame.add(pb);
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);

                LoadMaster master = new LoadMaster();
                master.addPropertyChangeListener(new LoadMasterPropertyChanegHandler(SwingWorkerExample.this));
                master.execute();
            }
        });
    }

    protected void showProgress(int value) {
        pb.setValue(value);
    }

    protected void loadCompleted() {
        content.removeAll();
        content.setLayout(new GridLayout(0, 1));
        content.add(new JLabel("All your base are belong to us"));
        content.revalidate();

        LoadStuffWorker stuffWorker = new LoadStuffWorker(this);
        stuffWorker.execute();
    }

    protected void loadFailed() {
        content.removeAll();
        content.setLayout(new GridLayout(0, 1));
        content.add(new JLabel("Fail"));
        content.revalidate();
    }

    protected void setVersion(String value) {
        content.add(new JLabel("Version: " + value));
        content.revalidate();
    }

    protected void failed(String fail) {
        content.add(new JLabel(fail));
        content.revalidate();
    }

    public class LoadMaster extends SwingWorker<Void, Progress> {

        @Override
        protected Void doInBackground() throws Exception {
            System.out.println("Working hard here, nothing to see...");
            for (int index = 0; index < 100; index++) {
                Thread.sleep(10);
                setProgress(index);
            }
            return null;
        }

        @Override
        protected void done() {
            try {
                get();
            } catch (Exception e) {
            }
        }

    }

    public class LoadStuffWorker extends SwingWorker<String, Void> {

        private SwingWorkerExample example;

        public LoadStuffWorker(SwingWorkerExample example) {
            this.example = example;
        }

        @Override
        protected String doInBackground() throws Exception {
            System.out.println("Hanging about in the background");
            Thread.sleep(3000);
            return "Hello from the dark side";
        }

        @Override
        protected void done() {
            try {
                String value = get();
                example.setVersion(value);
            } catch (InterruptedException | ExecutionException ex) {
                example.failed("Fail while doing version check");
            }
        }

    }

    public class Progress {
    }

    public class LoadMasterPropertyChanegHandler implements PropertyChangeListener {

        private SwingWorkerExample example;

        public LoadMasterPropertyChanegHandler(SwingWorkerExample example) {
            this.example = example;
        }

        @Override
        public void propertyChange(PropertyChangeEvent evt) {
            System.out.println(evt.getPropertyName());
            if ("progress".equalsIgnoreCase(evt.getPropertyName())) {
                int value = (int) evt.getNewValue();
                example.showProgress(value);
            } else if ("state".equalsIgnoreCase(evt.getPropertyName())) {
                SwingWorker worker = (SwingWorker) evt.getSource();
                if (worker.isDone()) {
                    try {
                        worker.get();
                        example.loadCompleted();
                    } catch (InterruptedException | ExecutionException exp) {
                        example.loadFailed();
                    }
                }
            }
        }

    }

}