vo: add progress monitor for registry endpoint updater

When the list of registries is queried to update the list of available
registries, Downloader monitor component is displayed to show progress.

This is useful, and an improvement, but it should really work
differently than this - there ought to be a single registry selection
model for the whole application not one for each window.  One day.

vo/src/main/uk/ac/starlink/vo/RegistrySelector.java

@@ -3,6 +3,8 @@
 import java.awt.Component;
 import java.awt.Dimension;
 import java.awt.event.ActionEvent;
+import java.awt.event.ItemEvent;
+import java.awt.event.ItemListener;
 import java.io.IOException;
 import java.util.ArrayList;
 import java.util.HashSet;
@@ -24,6 +26,7 @@
 import javax.swing.MutableComboBoxModel;
 import javax.swing.SwingUtilities;
 import javax.swing.text.JTextComponent;
+import uk.ac.starlink.util.gui.Downloader;
 
 /**
  * Component for selecting a registry service.
@@ -38,6 +41,7 @@ public class RegistrySelector extends JPanel {
 
     private final JComboBox comboBox_;
     private final Action updateAction_;
+    private final EndpointDownloader endpointDownloader_;
     private RegistrySelectorModel model_;
     private static final Logger logger_ =
         Logger.getLogger( "uk.ac.starlink.vo" );
@@ -74,34 +78,34 @@ public void configureEditor( ComboBoxEditor editor, Object item ) {
         comboBox_.setEditable( true );
         comboBox_.setToolTipText( "Endpoint of VOResource 1.0"
                                 + " registry service" );
+        comboBox_.addItemListener( new ItemListener() {
+            public void itemStateChanged( ItemEvent evt ) {
+                endpointDownloader_.setQuery( getRegKey() );
+            }
+        } );
+
+        /* Set up an item for downloading other registry endpoints. */
+        endpointDownloader_ = new EndpointDownloader();
 
         /* Set up an action to update the selector box contents. */
         updateAction_ = new AbstractAction( "Update Registry List" ) {
             public void actionPerformed( ActionEvent evt ) {
-                final String reg = (String) comboBox_.getSelectedItem();
+                final RegKey regKey = getRegKey();
+                endpointDownloader_.setQuery( regKey );
                 updateAction_.setEnabled( false );
                 new Thread( "Registry search" ) {
                     public void run() {
-                        try {
-                            final String[] acurls =
-                                model_.getProtocol()
-                                      .discoverRegistryUrls( reg );
-                            SwingUtilities.invokeLater( new Runnable() {
-                                public void run() {
+                        final String[] acurls =
+                            endpointDownloader_.waitForData();
+                        SwingUtilities.invokeLater( new Runnable() {
+                            public void run() {
+                                updateAction_.setEnabled( true );
+                                if ( model_.getProtocol() == regKey.proto_ &&
+                                     acurls != null ) {
                                     updateSelector( acurls );
                                 }
-                            } );
-                        }
-                        catch ( IOException e ) {
-                            logger_.warning( "Registry search failed: " + e );
-                        }
-                        finally {
-                            SwingUtilities.invokeLater( new Runnable() {
-                                public void run() {
-                                    updateAction_.setEnabled( true );
-                                }
-                            } );
-                        }
+                            }
+                        } );
                     }
                 }.start();
             }
@@ -114,6 +118,8 @@ public void run() {
         setLayout( new BoxLayout( this, BoxLayout.X_AXIS ) );
         add( new JLabel( "Registry: " ) );
         add( comboBox_ );
+        add( Box.createHorizontalStrut( 5 ) );
+        add( endpointDownloader_.createMonitorComponent() );
 
         /* Install the model. */
         setModel( model );
@@ -129,6 +135,7 @@ public void setModel( RegistrySelectorModel model ) {
         ComboBoxModel urlModel = model.getUrlSelectionModel();
         comboBox_.setModel( urlModel );
         updateAction_.setEnabled( urlModel instanceof MutableComboBoxModel );
+        endpointDownloader_.setQuery( getRegKey() );
     }
 
     /**
@@ -166,6 +173,17 @@ public Action getRegistryUpdateAction() {
         return updateAction_;
     }
 
+    /**
+     * Returns an object indicating which registry is currently selected.
+     * 
+     * @return  registry identifier
+     */
+    private RegKey getRegKey() {
+        RegistryProtocol proto = model_.getProtocol();
+        String reg = (String) comboBox_.getSelectedItem();
+        return new RegKey( proto, reg );
+    }
+
     /**
      * Adds new access URLs to the combo box.  Must be called from the
      * event dispatch thread.
@@ -202,4 +220,74 @@ private void updateSelector( String[] acurls ) {
             }
         }
     }
+
+    /**
+     * Downloader implementation for downloading registry endpoint URLs.
+     */
+    private static class EndpointDownloader extends Downloader<String[]> {
+        private RegKey key_;
+
+        /**
+         * Constructor.
+         */
+        EndpointDownloader() {
+            super( String[].class, "Registry service URLs" );
+        }
+
+        /**
+         * Sets the configuration for which to query registry endpoints.
+         *
+         * @param  key  registry identification object
+         */
+        public void setQuery( RegKey key ) {
+            clearData();
+            key_ = key;
+        }
+
+        public String[] attemptReadData() throws IOException {
+            return key_.proto_.discoverRegistryUrls( key_.reg_ );
+        }
+    }
+
+    /**
+     * Aggregates RegistryProtocol and a URL endpoint to specify a
+     * registry access.
+     */
+    private static class RegKey {
+        final RegistryProtocol proto_;
+        final String reg_;
+
+        /**
+         * Constructor.
+         *
+         * @param  proto  registry access protocol
+         * @param  reg   registry endpoint URL
+         */
+        RegKey( RegistryProtocol proto, String reg ) {
+            proto_ = proto;
+            reg_ = reg;
+        }
+
+        @Override
+        public int hashCode() {
+            return proto_.hashCode() * 5001 + reg_.hashCode();
+        }
+
+        @Override
+        public boolean equals( Object o ) {
+            if ( o instanceof RegKey ) {
+                RegKey other = (RegKey) o;
+                return this.proto_.equals( other.proto_ )
+                    && this.reg_.equals( other.reg_ );
+            }
+            else {
+                return false;
+            }
+        }
+
+        @Override
+        public String toString() {
+            return proto_ + "-" + reg_;
+        }
+    }
 }