DPML Notify

[mcconnell AT dpml.net]

Author: mcconnell AT dpml.net
Date: Wed Jun  1 15:11:32 2005
New Revision: 2687

Added:
   
development/main/transit/core/handler/src/main/net/dpml/transit/model/HostAvailabilityEvent.java
Modified:
   
development/main/depot/prefs/src/main/net/dpml/depot/prefs/HostManagerPanel.java
   
development/main/depot/prefs/src/main/net/dpml/depot/prefs/LayoutComboBoxModel.java
   
development/main/transit/core/handler/src/main/net/dpml/transit/host/ClassicResourceHost.java
   
development/main/transit/core/handler/src/main/net/dpml/transit/manager/CacheManager.java
   
development/main/transit/core/handler/src/main/net/dpml/transit/manager/HostManager.java
   
development/main/transit/core/handler/src/main/net/dpml/transit/manager/RegistryManager.java
   
development/main/transit/core/handler/src/main/net/dpml/transit/model/HostListener.java
   
development/main/transit/core/handler/src/main/net/dpml/transit/model/RegistryModel.java
Log:
Work-in-progress on host availability.

Modified: 
development/main/depot/prefs/src/main/net/dpml/depot/prefs/HostManagerPanel.java
==============================================================================
--- 
development/main/depot/prefs/src/main/net/dpml/depot/prefs/HostManagerPanel.java
    (original)
+++ 
development/main/depot/prefs/src/main/net/dpml/depot/prefs/HostManagerPanel.java
    Wed Jun  1 15:11:32 2005
@@ -60,6 +60,7 @@
 import net.dpml.transit.model.HostEnabledEvent;
 import net.dpml.transit.model.HostTrustedEvent;
 import net.dpml.transit.model.HostPriorityEvent;
+import net.dpml.transit.model.HostAvailabilityEvent;
 
 /**
  * A interactive panel that presents the preferences for a single host.
@@ -336,6 +337,14 @@
     {
     }
 
+   /**
+    * Notify a consumer of a change to the availability status.
+    * @param event the host event
+    */
+    public void availabilityChanged( HostAvailabilityEvent event )
+    {
+    }
+
     //--------------------------------------------------------------
     // PropertyChangeListener
     //--------------------------------------------------------------

Modified: 
development/main/depot/prefs/src/main/net/dpml/depot/prefs/LayoutComboBoxModel.java
==============================================================================
--- 
development/main/depot/prefs/src/main/net/dpml/depot/prefs/LayoutComboBoxModel.java
 (original)
+++ 
development/main/depot/prefs/src/main/net/dpml/depot/prefs/LayoutComboBoxModel.java
 Wed Jun  1 15:11:32 2005
@@ -29,6 +29,7 @@
 import net.dpml.transit.model.HostTrustedEvent;
 import net.dpml.transit.model.HostPriorityEvent;
 import net.dpml.transit.model.HostLayoutEvent;
+import net.dpml.transit.model.HostAvailabilityEvent;
 import net.dpml.transit.model.LayoutModel;
 import net.dpml.transit.model.LayoutRegistryListener;
 import net.dpml.transit.model.LayoutRegistryEvent;
@@ -149,5 +150,13 @@
         }
     }
 
+
+   /**
+    * Notify a consumer of a change to the availability status.
+    * @param event the host event
+    */
+    public void availabilityChanged( HostAvailabilityEvent event )
+    {
+    }
 }
 

Modified: 
development/main/transit/core/handler/src/main/net/dpml/transit/host/ClassicResourceHost.java
==============================================================================
--- 
development/main/transit/core/handler/src/main/net/dpml/transit/host/ClassicResourceHost.java
       (original)
+++ 
development/main/transit/core/handler/src/main/net/dpml/transit/host/ClassicResourceHost.java
       Wed Jun  1 15:11:32 2005
@@ -69,6 +69,7 @@
 import net.dpml.transit.model.HostEnabledEvent;
 import net.dpml.transit.model.HostTrustedEvent;
 import net.dpml.transit.model.HostPriorityEvent;
+import net.dpml.transit.model.HostAvailabilityEvent;
 import net.dpml.transit.model.HostLayoutEvent;
 import net.dpml.transit.model.Logger;
 
@@ -189,6 +190,14 @@
     {
     }
 
+   /**
+    * Notify a consumer of a change to the available status.
+    * @param event the availability change event
+    */
+    public void availabilityChanged( HostAvailabilityEvent event )
+    {
+    }
+
     // 
------------------------------------------------------------------------
     // ResourceHost
     // 
------------------------------------------------------------------------

Modified: 
development/main/transit/core/handler/src/main/net/dpml/transit/manager/CacheManager.java
==============================================================================
--- 
development/main/transit/core/handler/src/main/net/dpml/transit/manager/CacheManager.java
   (original)
+++ 
development/main/transit/core/handler/src/main/net/dpml/transit/manager/CacheManager.java
   Wed Jun  1 15:11:32 2005
@@ -45,6 +45,13 @@
 import net.dpml.transit.model.CacheListener;
 import net.dpml.transit.model.FileChangeEvent;
 import net.dpml.transit.model.HostNodeEvent;
+import net.dpml.transit.model.HostChangeEvent;
+import net.dpml.transit.model.HostEnabledEvent;
+import net.dpml.transit.model.HostTrustedEvent;
+import net.dpml.transit.model.HostPriorityEvent;
+import net.dpml.transit.model.HostLayoutEvent;
+import net.dpml.transit.model.HostAvailabilityEvent;
+import net.dpml.transit.model.HostListener;
 import net.dpml.transit.model.ModelException;
 import net.dpml.transit.model.Logger;
 
@@ -64,6 +71,7 @@
     // state
     // 
------------------------------------------------------------------------
 
+    private final AvailabilityListener m_availabilityListener = new 
AvailabilityListener();
     private final LayoutRegistryManager m_layout;
     private final List m_list = new LinkedList();
 
@@ -225,6 +233,14 @@
             {
                 // ignore
             }
+            try
+            {
+                model.removeHostListener( m_availabilityListener );
+            }
+            catch( Throwable e )
+            {
+                // ignore
+            }
         }
     }
 
@@ -350,6 +366,67 @@
     }
 
     // 
------------------------------------------------------------------------
+    // HostListener
+    // 
------------------------------------------------------------------------
+
+    private class AvailabilityListener implements HostListener
+    {
+       /**
+        * Notify a consumer of an aggregated set of changes.
+        * @param event the host change event
+        */
+        public void hostChanged( HostChangeEvent event )
+        {
+        }
+    
+       /**
+        * Notify a consumer of a change to the enabled state.
+        * @param event the host event
+        */
+        public void enabledStateChanged( HostEnabledEvent event )
+        {
+        }
+
+       /**
+        * Notify a consumer of a change to the trusted state.
+        * @param event the host event
+        */
+        public void trustedStateChanged( HostTrustedEvent event )
+        {
+        }
+    
+       /**
+        * Notify a consumer of a change to the host priority.
+        * @param event the host event
+        */
+        public void priorityChanged( HostPriorityEvent event )
+        {
+        }
+
+       /**
+        * Notify a consumer of a change to the host resolver.
+        * @param event the host resolver change event
+        */
+        public void layoutChanged( HostLayoutEvent event )
+        {
+        }
+
+       /**
+        * Notify a consumer of a change to availability status of a host.
+        * @param event the host availability event
+        */
+        public void availabilityChanged( HostAvailabilityEvent event )
+        {
+            System.out.println( 
+              "# HOST AVAILABILITY CHANGE " 
+              + event.getHostModel().getID() 
+              + ", " 
+              + event.getAvailability() );
+        }
+
+    }
+
+    // 
------------------------------------------------------------------------
     // internal
     // 
------------------------------------------------------------------------
 
@@ -371,6 +448,7 @@
             }
             m_list.add( model );
             model.addPluginListener( this );
+            model.addHostListener( m_availabilityListener );
             if( notify )
             {
                 HostAddedEvent event = new HostAddedEvent( this, model, 
priority );
@@ -389,6 +467,7 @@
             {
                 m_list.remove( model );
                 model.removePluginListener( this );
+                model.removeHostListener( m_availabilityListener );
                 HostRemovedEvent event = new HostRemovedEvent( this, model );
                 super.enqueueEvent( event );
             }

Modified: 
development/main/transit/core/handler/src/main/net/dpml/transit/manager/HostManager.java
==============================================================================
--- 
development/main/transit/core/handler/src/main/net/dpml/transit/manager/HostManager.java
    (original)
+++ 
development/main/transit/core/handler/src/main/net/dpml/transit/manager/HostManager.java
    Wed Jun  1 15:11:32 2005
@@ -19,10 +19,12 @@
 package net.dpml.transit.manager;
 
 import java.io.IOException;
+import java.util.Date;
 import java.util.Map;
 import java.util.ArrayList;
 import java.util.EventObject;
 import java.util.EventListener;
+import java.util.List;
 import java.net.URI;
 import java.net.URL;
 import java.net.UnknownHostException;
@@ -31,21 +33,22 @@
 import java.util.prefs.PreferenceChangeEvent;
 import java.util.prefs.PreferenceChangeListener;
 
+import net.dpml.transit.model.HostAvailabilityEvent;
 import net.dpml.transit.model.HostEnabledEvent;
-import net.dpml.transit.model.HostModel;
-import net.dpml.transit.model.HostEvent;
 import net.dpml.transit.model.HostChangeEvent;
+import net.dpml.transit.model.HostEvent;
 import net.dpml.transit.model.HostLayoutEvent;
 import net.dpml.transit.model.HostListener;
+import net.dpml.transit.model.HostModel;
+import net.dpml.transit.model.HostNameEvent;
+import net.dpml.transit.model.HostPriorityEvent;
+import net.dpml.transit.model.HostTrustedEvent;
 import net.dpml.transit.model.LayoutModel;
 import net.dpml.transit.model.LayoutRegistryModel;
 import net.dpml.transit.model.Logger;
-import net.dpml.transit.model.HostNameEvent;
 import net.dpml.transit.model.ModelException;
-import net.dpml.transit.model.HostPriorityEvent;
 import net.dpml.transit.model.PluginModel;
 import net.dpml.transit.model.PluginChangeEvent;
-import net.dpml.transit.model.HostTrustedEvent;
 
 import net.dpml.transit.network.RequestIdentifier;
 
@@ -71,12 +74,13 @@
     private boolean m_enabled = false;
     private boolean m_trusted = false;
     private LayoutModel m_layout;
-    private boolean m_available = false;
     private int m_priority = 600;
     private RequestIdentifier m_identifier;
     private PasswordAuthentication m_authentication;
     private boolean m_bootstrap = false;
 
+    private Throwable m_error;
+
     // 
------------------------------------------------------------------------
     // constructor
     // 
------------------------------------------------------------------------
@@ -89,20 +93,57 @@
         m_layoutRegistry = registry;
         m_bootstrap = prefs.getBoolean( "bootstrap", false );
         m_id = prefs.name();
+
         m_name = prefs.get( "name", m_id );
         m_trusted = prefs.getBoolean( "trusted", m_trusted );
         m_enabled = prefs.getBoolean( "enabled", m_enabled );
         m_priority = prefs.getInt( "priority", m_priority );
         String layout = prefs.get( "layout", "classic" );
-        m_layout = registry.getLayoutModel( layout );
-        
-        m_base = resolveBase( prefs );
-        if( m_base != null )
+        m_layout = resolveLayoutModel( layout );
+
+        try
         {
+            m_base = resolveBase( prefs );
             m_index = resolveIndex( m_base, prefs );
             m_identifier = resolveRequestIdentifier( m_base, prefs );
             m_authentication = resolvePasswordAuthentication( prefs );
-            m_available = true;
+        }
+        catch( Throwable e )
+        {
+            setError( e );
+        }
+    }
+
+    private void setError( Throwable e )
+    {
+        if( null == m_error )
+        {
+            if( null != e )
+            {
+                // raise a non-available event
+                m_error = e;
+                HostAvailabilityEvent event = new HostAvailabilityEvent( 
this, false );
+                enqueueEvent( event );
+            }
+            else
+            {
+                // nothing changes
+            }
+        }
+        else
+        {
+            if( null == e )
+            {
+                // raise a available event
+                m_error = null;
+                HostAvailabilityEvent event = new HostAvailabilityEvent( 
this, true );
+                enqueueEvent( event );
+            }
+            else
+            {
+                // update the error state
+                m_error = e;
+            }
         }
     }
 
@@ -112,68 +153,59 @@
 
     public synchronized void update( URL base, URL index, boolean enabled, 
boolean trusted, LayoutModel layout )
     {
-        m_base = base;
-        m_enabled = enabled;
-        m_trusted = trusted;
-        m_layout = layout;
-
-        updateBaseURL();
-        updateTrusted();
-        updateEnabled();
-        updateLayoutModel();
+        storeBaseURL( base );
+        storeTrusted( trusted );
+        storeLayoutModel( layout );
+        storeEnabled( enabled );
+        storeModified();
     }
 
-    private void updateBaseURL()
+    private void storeBaseURL( URL base )
     {
         Preferences prefs = getPreferences();
-        if( null == m_base )
+        if( null == base )
         {
             prefs.remove( "base" );
         }
         else
         {
-            prefs.put( "base", m_base.toExternalForm() );
+            prefs.put( "base", base.toExternalForm() );
         }
     }
 
-    private void updateTrusted()
+    private void storeTrusted( boolean trusted )
     {
         Preferences prefs = getPreferences();
-        prefs.putBoolean( "trusted", m_trusted );
+        prefs.putBoolean( "trusted", trusted );
     }
 
-    public void updateEnabled()
+    private void storeEnabled( boolean enabled )
     {
         Preferences prefs = getPreferences();
-        prefs.putBoolean( "enabled", m_enabled );
+        prefs.putBoolean( "enabled", enabled );
     }
 
-    public void updateLayoutModel()
+    private void storeLayoutModel( LayoutModel layout )
     {
-        String id = m_layout.getID();
         Preferences prefs = getPreferences();
-        prefs.put( "layout", id );
-    }
-
-   /**
-    * Set the host authentication.
-    * @param auth the password authentication to use for host sign-on
-    */
-    public void setAuthentication( PasswordAuthentication auth ) throws 
IOException
-    {
-        m_authentication = auth;
-        Preferences prefs = getPreferences();
-        if( null == auth )
+        if( null == layout )
         {
-            prefs.putByteArray( "authentication", new byte[0] );
+            prefs.put( "layout", "classic" );
         }
         else
         {
-            byte[] bytes = CredentialsHelper.exportCredentials( 
m_authentication );
-            prefs.putByteArray( "authentication", bytes );
+            String id = layout.getID();
+            prefs.put( "layout", id );
         }
     }
 
+    private void storeModified()
+    {
+        Preferences prefs = getPreferences();
+        long timestamp = new Date().getTime();
+        prefs.putLong( "modified", timestamp );
+    }
+
     //----------------------------------------------------------------------
     // Comparable
     //----------------------------------------------------------------------
@@ -226,10 +258,7 @@
     */
     public int getPriority()
     {
-        synchronized( this )
-        {
-            return m_priority;
-        }
+        return m_priority;
     }
 
    /**
@@ -238,10 +267,7 @@
     */
     public boolean getAvailable()
     {
-        synchronized( this )
-        {
-            return m_base != null;
-        }
+        return ( null == m_error );
     }
 
    /**
@@ -250,10 +276,7 @@
     */
     public String getHostName()
     {
-        synchronized( this )
-        {
-            return m_name;
-        }
+        return m_name;
     }
 
    /**
@@ -262,10 +285,7 @@
     */
     public URL getBaseURL()
     {
-        synchronized( this )
-        {
-            return m_base;
-        }
+        return m_base;
     }
 
    /**
@@ -274,10 +294,7 @@
     */
     public URL getIndexURL()
     {
-        synchronized( this )
-        {
-            return m_index;
-        }
+        return m_index;
     }
 
    /**
@@ -286,10 +303,7 @@
     */
     public boolean getEnabled()
     {
-        synchronized( this )
-        {
-            return m_enabled;
-        }
+        return m_enabled;
     }
 
    /**
@@ -298,10 +312,7 @@
     */
     public boolean getTrusted()
     {
-        synchronized( this )
-        {
-            return m_trusted;
-        }
+        return m_trusted;
     }
 
    /**
@@ -310,10 +321,7 @@
     */
     public PasswordAuthentication getAuthentication()
     {
-        synchronized( this )
-        {
-            return m_authentication;
-        }
+        return m_authentication;
     }
 
    /**
@@ -322,10 +330,7 @@
     */
     public RequestIdentifier getRequestIdentifier()
     {
-        synchronized( this )
-        {
-            return m_identifier;
-        }
+        return m_identifier;
     }
 
    /**
@@ -334,10 +339,7 @@
     */
     public LayoutModel getLayoutModel()
     {
-        synchronized( this )
-        {
-            return m_layout;
-        }
+        return m_layout;
     }
 
    /**
@@ -410,24 +412,35 @@
             String id = event.getNewValue();
             try
             {
-                setLayoutModel( id );
+                m_layout = resolveLayoutModel( id );
+                HostLayoutEvent e = new HostLayoutEvent( this, m_layout );
+                enqueueEvent( e );
             }
             catch( ModelException e )
             {
+                setError( e );
                 final String error = 
                   "Host layout not set due to an unexpected error.";
                 getLogger().error( error, e );
                 return;
             }
-            LayoutModel layout = getLayoutModel();
-            HostLayoutEvent e = new HostLayoutEvent( this, layout );
-            enqueueEvent( e );
         }
         else if( "modified".equals( key ) )
         {
-            // this is a trigger marking modification to any of the 
-            // attributes "base", "username", "password", "prompt" or 
"scheme"
-            // in which case we notify a host controller of the change via 
+            // This is a trigger marking modification to any of the 
+            // attributes "base", "index", "username", "password", "prompt" 
+            // or "scheme".
+            //
+            // If the value of the modified attribute is greater than zero
+            // this signals that the preceeding attributes are in a state 
+            // ready for propergation into the model.  If propergation
+            // raises an error the modified attribute will be reset. 
+            //
+            
+ 
+            // If the value of the modified attribute is greater than zero 
this
+            // signals a valid set of information that we can use in a host 
change
+            // event.  we notify a host controller of the change via 
             // a single HostChangeEvent
 
             synchronized( this )
@@ -436,8 +449,8 @@
                 try
                 {
                     URL base = resolveBase( prefs );
-                    URL index = resolveIndex( m_base, prefs );
-                    RequestIdentifier identifier = resolveRequestIdentifier( 
m_base, prefs );
+                    URL index = resolveIndex( base, prefs );
+                    RequestIdentifier identifier = resolveRequestIdentifier( 
base, prefs );
                     PasswordAuthentication authentication = 
resolvePasswordAuthentication( prefs );
 
                     m_base = base;
@@ -448,9 +461,11 @@
                     HostChangeEvent e = 
                       new HostChangeEvent( this, base, index, identifier, 
authentication );       
                     enqueueEvent( e );
+                    setError( null );
                 }
                 catch( UnknownHostException uhe )
                 {
+                    setError( uhe );
                     final String error = 
                       "Unable to propergate change event due to an 
unresolved host."
                       + "\nPreferences Node: " + prefs
@@ -459,6 +474,7 @@
                 }
                 catch( IOException ioe )
                 {
+                    setError( ioe );
                     final String error = 
                       "Unable to propergate change event due to an 
unexpected IO error."
                       + "\nPreferences Node: " + prefs;
@@ -472,11 +488,30 @@
     // internal
     //----------------------------------------------------------------------
 
-    public void setLayoutModel( String id ) throws ModelException
+   /**
+    * Set the host authentication.
+    * @param auth the password authentication to use for host sign-on
+    */
+    public void setAuthentication( PasswordAuthentication auth ) throws 
IOException
+    {
+        m_authentication = auth;
+        Preferences prefs = getPreferences();
+        if( null == auth )
+        {
+            prefs.putByteArray( "authentication", new byte[0] );
+        }
+        else
+        {
+            byte[] bytes = CredentialsHelper.exportCredentials( 
m_authentication );
+            prefs.putByteArray( "authentication", bytes );
+        }
+    }
+
+    public LayoutModel resolveLayoutModel( String id ) throws ModelException
     {
         if( ( null != m_layout ) && m_layout.getID().equals( id ) )
         {
-            return;
+            return m_layout;
         }
         else
         {
@@ -507,12 +542,16 @@
                 }
             }
 
-            m_layout = layout;
+            return layout;
         }
     }
 
     private RequestIdentifier resolveRequestIdentifier( URL base, 
Preferences prefs )
     {
+        if( null == base )
+        {
+            throw new NullPointerException( "base" );
+        }
         String scheme = prefs.get( "scheme", "" );
         String prompt = prefs.get( "prompt", "" );
         String protocol = base.getProtocol();
@@ -548,7 +587,10 @@
         String baseSpec = prefs.get( "base", null );
         if( null == baseSpec )
         {
-            return null;
+            final String error =  
+              "Undefined host base url"
+              + "\nHost ID: " + prefs.name();
+            throw new ModelException( error );
         }
 
         //
@@ -568,7 +610,7 @@
     {
         if( null == base )
         {
-            return null;
+            throw new NullPointerException( "base" );
         }
         String indexSpec = prefs.get( "index", null );
         if( null != indexSpec )
@@ -587,6 +629,10 @@
         {
             super.processPluginChangeEvent( (PluginChangeEvent) event );
         }
+        else if( event instanceof HostAvailabilityEvent )
+        {
+            processHostAvailabilityEvent( (HostAvailabilityEvent) event );
+        }
         else if( event instanceof HostChangeEvent )
         {
             processHostChangeEvent( (HostChangeEvent) event );
@@ -630,7 +676,26 @@
             {
                 final String error =
                   "HostListener enabled status change notification error.";
-                getLogger().error( error, e );
+                getLogger().warn( error, e );
+            }
+        }
+    }
+
+    private void processHostAvailabilityEvent( HostAvailabilityEvent event )
+    {
+        HostListener[] listeners = getHostListeners();
+        for( int i=0; i<listeners.length; i++ )
+        {
+            HostListener listener = listeners[i];
+            try
+            {
+                listener.availabilityChanged( event );
+            }
+            catch( Throwable e )
+            {
+                final String error =
+                  "HostListener availability change notification error.";
+                getLogger().warn( error, e );
             }
         }
     }
@@ -649,7 +714,7 @@
             {
                 final String error =
                   "HostListener trusted status change notification error.";
-                getLogger().error( error, e );
+                getLogger().warn( error, e );
             }
         }
     }
@@ -668,7 +733,7 @@
             {
                 final String error =
                   "HostListener resolver change notification error.";
-                getLogger().error( error, e );
+                getLogger().warn( error, e );
             }
         }
     }
@@ -687,7 +752,7 @@
             {
                 final String error =
                   "HostListener priority change notification error.";
-                getLogger().error( error, e );
+                getLogger().warn( error, e );
             }
         }
     }
@@ -706,7 +771,7 @@
             {
                 final String error =
                   "HostListener change notification error.";
-                getLogger().error( error, e );
+                getLogger().warn( error, e );
             }
         }
     }

Modified: 
development/main/transit/core/handler/src/main/net/dpml/transit/manager/RegistryManager.java
==============================================================================
--- 
development/main/transit/core/handler/src/main/net/dpml/transit/manager/RegistryManager.java
        (original)
+++ 
development/main/transit/core/handler/src/main/net/dpml/transit/manager/RegistryManager.java
        Wed Jun  1 15:11:32 2005
@@ -73,9 +73,13 @@
             {
                 String name = names[i];
                 Preferences p = prefs.node( name );
-                addContentModel( p, false );
+                addContentManager( p, false );
             }
         }
+        catch( ModelException e )
+        {
+            throw e;
+        }
         catch( Exception e )
         {
             final String error = 
@@ -115,9 +119,62 @@
                 return manager;
             }
         }
+
+        //
+        // check for a system property that defines the plugin uri
+        //
+
+        String spec = "dpml.transit.content.plugin." + type;
+        String value = System.getProperty( spec );
+        if( null != value )
+        {
+            try
+            {
+                URI uri = new URI( value );
+                return addContentManager( type, type, uri );
+            }
+            catch( Throwable e )
+            {
+                final String error = 
+                  "Cannot construct content handler for system property 
specification."
+                  + "\nContent Type ID: " + type 
+                  + "\nSystem Defined URI: " + value;
+                IllegalArgumentException exception = 
+                   new IllegalArgumentException( error );
+                exception.initCause( e );
+                throw exception;
+            }
+        }
+
         return null;
     }
 
+   /**
+    * Register a new content manager.
+    *
+    * @return the content manager
+    */
+    public ContentManager addContentManager( String type, String title, URI 
uri ) throws ModelException
+    {
+        if( null == type )
+        {
+            throw new NullPointerException( "type" );
+        }
+        if( null == title )
+        {
+            throw new NullPointerException( "title" );
+        }
+        if( null == uri )
+        {
+            throw new NullPointerException( "uri" );
+        }
+
+        Preferences prefs = getPreferences().node( type );
+        prefs.put( "title", title );
+        prefs.put( "uri", uri.toString() );
+        return addContentManager( prefs, true );
+    }
+
     public void removeContentModel( String type ) throws ModelException
     {
         try
@@ -173,47 +230,25 @@
     }
 
     // 
------------------------------------------------------------------------
-    // RegistryManager
+    // RegistryModel
     // 
------------------------------------------------------------------------
 
    /**
     * Register a new content model.
     *
+    * @param type the content type identifier
+    * @param title the title of the content model
+    * @param plugin the content plugin uri
     * @return the content model
     */
-    public ContentModel addContentModel( String type, String title, URI uri )
+    public ContentModel addContentModel( String type, String title, URI 
plugin ) throws ModelException
     {
-        if( null == type )
-        {
-            throw new NullPointerException( "type" );
-        }
-        if( null == title )
-        {
-            throw new NullPointerException( "title" );
-        }
-        if( null == uri )
-        {
-            throw new NullPointerException( "uri" );
-        }
-
-        Preferences prefs = getPreferences().node( type );
-        prefs.put( "title", title );
-        prefs.put( "uri", uri.toString() );
-        return addContentModel( prefs, true );
+        return addContentManager( type, title, plugin );
     }
 
     public ContentModel getContentModel( String type )
     {
-        ContentModel[] models = getContentModels();
-        for( int i=0; i<models.length; i++ )
-        {
-            ContentModel model = models[i];
-            if( type.equals( model.getContentType() ) )
-            {
-                return model;
-            }
-        }
-        return null;
+        return getContentManager( type );
     }
 
    /**
@@ -265,7 +300,16 @@
     public void childAdded( NodeChangeEvent event )
     {
         Preferences prefs = event.getChild();
-        addContentModel( prefs, true );
+        try
+        {
+            addContentManager( prefs, true );
+        }
+        catch( ModelException e )
+        {
+            String message = e.getMessage();
+            Throwable cause = e.getCause();
+            getLogger().error( message, cause );
+        }
     }
 
     public void childRemoved( NodeChangeEvent event )
@@ -278,24 +322,20 @@
     // internal
     // 
------------------------------------------------------------------------
 
-    private ContentModel addContentModel( Preferences prefs, boolean notify )
+    private ContentManager addContentManager( Preferences prefs, boolean 
notify ) throws ModelException
     {
         Logger logger = getLogger();
-        ContentModel model = new ContentManager( logger, prefs );
+        ContentManager model = new ContentManager( logger, prefs );
         String type = model.getContentType();
         synchronized( m_list )
         {
-            Iterator iterator = m_list.iterator();
-            while( iterator.hasNext() )
+            ContentModel m = getContentModel( type );
+            if( null != m )
             {
-                ContentModel d = (ContentModel) iterator.next();
-                if( type.equals( d.getContentType() ) )
-                {
-                    final String error = 
-                      "Content type already registered."
-                      + "\nType: " + type;
-                    throw new IllegalArgumentException( error );
-                }
+                final String error = 
+                  "Content type already registered."
+                  + "\nType: " + type;
+                  throw new ModelException( error );
             }
             m_list.add( model );
             model.addPluginListener( this );

Added: 
development/main/transit/core/handler/src/main/net/dpml/transit/model/HostAvailabilityEvent.java
==============================================================================
--- (empty file)
+++ 
development/main/transit/core/handler/src/main/net/dpml/transit/model/HostAvailabilityEvent.java
    Wed Jun  1 15:11:32 2005
@@ -0,0 +1,50 @@
+/*
+ * Copyright 2005 Stephen J. McConnell.
+ *
+ * Licensed  under the  Apache License,  Version 2.0  (the "License");
+ * you may not use  this file  except in  compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed  under the  License is distributed on an "AS IS" BASIS,
+ * WITHOUT  WARRANTIES OR CONDITIONS  OF ANY KIND, either  express  or
+ * implied.
+ *
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package net.dpml.transit.model;
+
+import java.util.EventObject;
+
+/**
+ * An event signalling the change in the availability of a host.
+ */
+public class HostAvailabilityEvent extends EventObject
+{
+    private final boolean m_availability;
+
+   /**
+    * Creation of a new host availability event.
+    * @param host the host whos availability status has changed
+    * @param availability the avalability status
+    */
+    public HostAvailabilityEvent( HostModel host, boolean availability )
+    {
+        super( host );
+        m_availability = availability;
+    }
+    
+    public HostModel getHostModel()
+    {
+        return (HostModel) getSource();
+    }
+
+    public boolean getAvailability()
+    {
+        return m_availability;
+    }
+}

Modified: 
development/main/transit/core/handler/src/main/net/dpml/transit/model/HostListener.java
==============================================================================
--- 
development/main/transit/core/handler/src/main/net/dpml/transit/model/HostListener.java
     (original)
+++ 
development/main/transit/core/handler/src/main/net/dpml/transit/model/HostListener.java
     Wed Jun  1 15:11:32 2005
@@ -58,5 +58,11 @@
     */
     void layoutChanged( HostLayoutEvent event );
 
+   /**
+    * Notify a consumer of a change to availability status of a host.
+    * @param event the host availability event
+    */
+    void availabilityChanged( HostAvailabilityEvent event );
+
 }
 

Modified: 
development/main/transit/core/handler/src/main/net/dpml/transit/model/RegistryModel.java
==============================================================================
--- 
development/main/transit/core/handler/src/main/net/dpml/transit/model/RegistryModel.java
    (original)
+++ 
development/main/transit/core/handler/src/main/net/dpml/transit/model/RegistryModel.java
    Wed Jun  1 15:11:32 2005
@@ -35,7 +35,7 @@
     * @param plugin the content plugin uri
     * @return the content model
     */
-    ContentModel addContentModel( String type, String title, URI plugin );
+    ContentModel addContentModel( String type, String title, URI plugin ) 
throws ModelException;
 
    /**
     * Return a content model matching the supplied type. If the type is 
unknown