java multithreading swing executorservice swingworker

Understanding Java ExecutorService

I am trying the learn how to use executorservice of Java,

I was reading the following discussion Java thread simple queue

In this there is a sample example

ExecutorService service = Executors.newFixedThreadPool(10);
// now submit our jobs
service.submit(new Runnable() {
    public void run() {
    do_some_work();
   }
});
// you can submit any number of jobs and the 10 threads will work on them
// in order
...
// when no more to submit, call shutdown
service.shutdown();
// now wait for the jobs to finish
service.awaitTermination(Long.MAX_VALUE, TimeUnit.NANOSECONDS);

I tried implementing this solution, for this i have create one form and placed start and stop button but the problem which i am facing is, if i call this process on start button, it will hang complete form and we need to wait until all process is completed.

I also tried to read the following https://www3.ntu.edu.sg/home/ehchua/programming/java/J5e_multithreading.html

but till now i am not able to understand how to make it work, as after clicking the start button, i should get access back, suppose i want to stop the process.

can someone please guide me in right direction.

Thanks

To make my situation more clear, i am adding the code which i am testing.

Problems

1) complete form remain frozen when program execute. 2) Progressbar dont work, will display status only when all process is completed.

private void btnStartActionPerformed(java.awt.event.ActionEvent evt) {                                         
  TestConneciton();

}                                        

private void btnStopActionPerformed(java.awt.event.ActionEvent evt) {                                        
    flgStop = true;
}   

   private static final int MYTHREADS = 30;
private boolean flgStop = false;
public  void TestConneciton() {
    ExecutorService executor = Executors.newFixedThreadPool(MYTHREADS);
    String[] hostList = { "http://crunchify.com", "http://yahoo.com",
            "http://www.ebay.com", "http://google.com",
            "http://www.example.co", "https://paypal.com",
            "http://bing.com/", "http://techcrunch.com/",
            "http://mashable.com/", "http://thenextweb.com/",
            "http://wordpress.com/", "http://wordpress.org/",
            "http://example.com/", "http://sjsu.edu/",
            "http://ebay.co.uk/", "http://google.co.uk/",
            "http://www.wikipedia.org/",
            "http://en.wikipedia.org/wiki/Main_Page" };

    pbarStatus.setMaximum(hostList.length-1);
    pbarStatus.setValue(0);
    for (int i = 0; i < hostList.length; i++) {

        String url = hostList[i];
        Runnable worker = new MyRunnable(url);
        executor.execute(worker);
    }
    executor.shutdown();
    // Wait until all threads are finish
//        while (!executor.isTerminated()) {
// 
//        }
    System.out.println("\nFinished all threads");
}

public  class MyRunnable implements Runnable {
    private final String url;

    MyRunnable(String url) {
        this.url = url;
    }

    @Override
    public void run() {

        String result = "";
        int code = 200;
        try {
            if(flgStop == true)
            {
                //Stop thread execution
            }
            URL siteURL = new URL(url);
            HttpURLConnection connection = (HttpURLConnection) siteURL
                    .openConnection();
            connection.setRequestMethod("GET");
            connection.connect();

            code = connection.getResponseCode();
            pbarStatus.setValue(pbarStatus.getValue()+1);
            if (code == 200) {
                result = "Green\t";
            }
        } catch (Exception e) {
            result = "->Red<-\t";
        }
        System.out.println(url + "\t\tStatus:" + result);
    }
}

Solution

Per the ExecutorService API, this blocks:

service.awaitTermination(Long.MAX_VALUE, TimeUnit.NANOSECONDS);

API quote:

Blocks until all tasks have completed execution after a shutdown request, or the timeout occurs, or the current thread is interrupted, whichever happens first.

If you don't want this blocking your current thread, then perhaps you should call it in a different thread. Also, is yours is a Swing application, then consider using a SwingWorker, which I believe uses ExecutorServices "under the hood".

Based on your latest bit of code, I'd use

A SwingWorker to manage all the background threads.
I'd give the SwingWorker an ExecutorService
and also an ExecutorCompletionService that was initialized with the ExecutorService as this would allow me to grab task results as they're being completed
I'd fill it with Callables, not Runnables, since this would allow the task to return something, perhaps a String to indicate progress.
I'd set the SwingWorker's progress property to (100 * taskCount) / totalTaskCount and have my JProgressBar go from 0 to 100.
I'd then use the SwingWorker's publish/process method pairs extract the Strings returned by the callable.
I'd listen to the progress of the SwingWorker in my GUI with a PropertyChangeListener
And then make changes to the GUI from within this listener.
I'd change if (code == 200) { to if (code == HttpURLConnection.HTTP_OK) { to avoid magic numbers.
The JButton's Action would disable itself, then create a new SwingWorker object, add the worker's ProperChangeListener to the worker, then execute the worker.

For example

import java.awt.Font;
import java.awt.event.ActionEvent;
import java.awt.event.KeyEvent;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.CompletionService;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorCompletionService;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

import javax.swing.AbstractAction;
import javax.swing.Action;
import javax.swing.DefaultListModel;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.JProgressBar;
import javax.swing.JScrollPane;
import javax.swing.SwingUtilities;
import javax.swing.SwingWorker;

@SuppressWarnings("serial")
public class SwingExecutorCompletionService extends JPanel {
   public static final int MYTHREADS = 10;
   private static final int LIST_PROTOTYPE_SIZE = 120;
   private static final String LIST_PROTOTYPE_STRING = "%" + LIST_PROTOTYPE_SIZE + "s";
   public static final String[] HOST_LIST = { 
      "http://crunchify.com",
      "http://yahoo.com", 
      "http://www.ebay.com", 
      "http://google.com",
      "http://www.example.co", 
      "https://paypal.com", 
      "http://bing.com/",
      "http://techcrunch.com/", 
      "http://mashable.com/",
      "http://thenextweb.com/", 
      "http://wordpress.com/",
      "http://wordpress.org/", 
      "http://example.com/", 
      "http://sjsu.edu/",
      "http://ebay.co.uk/", 
      "http://google.co.uk/",
      "http://www.wikipedia.org/", 
      "http://en.wikipedia.org/wiki/Main_Page" };

   private JProgressBar pbarStatus = new JProgressBar(0, 100);
   private JButton doItButton = new JButton(new DoItAction("Do It", KeyEvent.VK_D));
   private DefaultListModel<String> listModel = new DefaultListModel<>();
   private JList<String> resultList = new JList<>(listModel);

   public SwingExecutorCompletionService() {
      resultList.setVisibleRowCount(10);
      resultList.setPrototypeCellValue(String.format(LIST_PROTOTYPE_STRING, ""));
      resultList.setFont(new Font(Font.MONOSPACED, Font.PLAIN, 12));

      add(pbarStatus);
      add(doItButton);
      add(new JScrollPane(resultList, JScrollPane.VERTICAL_SCROLLBAR_ALWAYS, 
            JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED));
   }

   public void addToCompletionList(String element) {
      listModel.addElement(element);
   }

   public void setStatusValue(int progress) {
      pbarStatus.setValue(progress);
   }

   class DoItAction extends AbstractAction {
      public DoItAction(String name, int mnemonic) {
         super(name);
         putValue(MNEMONIC_KEY, mnemonic);
      }

      @Override
      public void actionPerformed(ActionEvent e) {
         setEnabled(false);
         DoItWorker worker = new DoItWorker(HOST_LIST, MYTHREADS);
         SwingExecutorCompletionService gui = SwingExecutorCompletionService.this;
         PropertyChangeListener workerListener = new WorkerChangeListener(gui, this);
         worker.addPropertyChangeListener(workerListener);
         worker.execute();
      }
   }

   private static void createAndShowGui() {
      SwingExecutorCompletionService mainPanel = new SwingExecutorCompletionService();

      JFrame frame = new JFrame("Swing ExecutorCompletionService");
      frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
      frame.getContentPane().add(mainPanel);
      frame.pack();
      frame.setLocationByPlatform(true);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGui();
         }
      });
   }
}

class MyCallable implements Callable<String> {
   private static final String RED = "->Red<-";
   private static final String GREEN = "Green";
   private final String url;
   private volatile boolean flgStop;

   MyCallable(String url) {
      this.url = url;
   }

   @Override
   public String call() throws Exception {
      String result = "";
      int code = HttpURLConnection.HTTP_OK;
      try {
         // if(flgStop == true)
         if (flgStop) {
            // Stop thread execution
         }
         URL siteURL = new URL(url);
         HttpURLConnection connection = (HttpURLConnection) siteURL
               .openConnection();
         connection.setRequestMethod("GET");
         connection.connect();

         code = connection.getResponseCode();

         // No don't set the prog bar in a background thread!
         // !! pbarStatus.setValue(pbarStatus.getValue()+1); 
         // avoid magic numbers
         if (code == HttpURLConnection.HTTP_OK) {
            result = GREEN;
         }
      } catch (Exception e) {
         result = RED;
      }
      return String.format("%-40s %s", url + ":", result);
   }

}

class WorkerChangeListener implements PropertyChangeListener {
   private Action action;
   private SwingExecutorCompletionService gui;

   public WorkerChangeListener(SwingExecutorCompletionService gui, Action button) {
      this.gui = gui;
      this.action = button;
   }

   @Override
   public void propertyChange(PropertyChangeEvent evt) {
      DoItWorker worker = (DoItWorker)evt.getSource();
      if (evt.getNewValue() == SwingWorker.StateValue.DONE) {
         action.setEnabled(true);
         try {
            worker.get();
         } catch (InterruptedException e) {
            e.printStackTrace();
         } catch (ExecutionException e) {
            e.printStackTrace();
         }
      } else if (DoItWorker.INTERMEDIATE_RESULT.equals(evt.getPropertyName())) {
         gui.addToCompletionList(evt.getNewValue().toString());
      } else if ("progress".equals(evt.getPropertyName())) {
         gui.setStatusValue(worker.getProgress());
      }
   }
}

class DoItWorker extends SwingWorker<Void, String> {
   public static final String INTERMEDIATE_RESULT = "intermediate result";
   private static final long TIME_OUT = 5;
   private static final TimeUnit UNIT = TimeUnit.MINUTES;

   private String intermediateResult;
   private ExecutorService executor;
   private CompletionService<String> completionService;
   private String[] hostList;

   public DoItWorker(String[] hostList, int myThreads) {
      this.hostList = hostList;
      executor = Executors.newFixedThreadPool(myThreads);
      completionService = new ExecutorCompletionService<>(executor);
   }

   @Override
   protected Void doInBackground() throws Exception {
      for (int i = 0; i < hostList.length; i++) {

         String url = hostList[i];
         Callable<String> callable = new MyCallable(url);
         completionService.submit(callable);
      }
      executor.shutdown();
      for (int i = 0; i < hostList.length; i++) {
         String result = completionService.take().get();
         publish(result);
         int progress = (100 * i) / hostList.length;
         setProgress(progress);
      }
      executor.awaitTermination(TIME_OUT, UNIT);
      setProgress(100);
      return null;
   }

   @Override
   protected void process(List<String> chunks) {
      for (String chunk : chunks) {
         setIntermediateResult(chunk);
      }
   }

   private void setIntermediateResult(String intermediateResult) {
      String oldValue = this.intermediateResult;
      String newValue = intermediateResult;
      this.intermediateResult = intermediateResult;
      firePropertyChange(INTERMEDIATE_RESULT, oldValue, newValue);
   }

}

Which would look and run like:

enter image description here