DPML Notify

[mcconnell AT dpml.net]

Author: mcconnell AT dpml.net
Date: Fri Mar 25 17:15:36 2005
New Revision: 2137

Added:
   
development/main/metro/context/impl/src/main/net/dpml/context/impl/ContextInvocationHandler.java
Log:
add a context innvocation handler

Added: 
development/main/metro/context/impl/src/main/net/dpml/context/impl/ContextInvocationHandler.java
==============================================================================
--- (empty file)
+++ 
development/main/metro/context/impl/src/main/net/dpml/context/impl/ContextInvocationHandler.java
    Fri Mar 25 17:15:36 2005
@@ -0,0 +1,210 @@
+/*
+ * Copyright 2004 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.context.impl;
+
+import java.lang.reflect.InvocationHandler;
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.UndeclaredThrowableException;
+import java.lang.reflect.Method;
+import java.util.Hashtable;
+import java.util.Map;
+
+import net.dpml.meta.info.Type;
+import net.dpml.meta.info.EntryDescriptor;
+
+/**
+ * This makes a dynamic proxy for an object.  The object can be represented
+ * by one, some or all of it's interfaces.
+ *
+ * @author <a href="mailto:dev-dpml AT lists.ibiblio.org";>The Digital Product 
Meta Library</a>
+ * @version $Id: ApplianceInvocationHandler.java 2106 2005-03-21 18:46:10Z 
mcconnell AT dpml.net $
+ */
+public final class ContextInvocationHandler
+  implements InvocationHandler
+{
+    //-------------------------------------------------------------------
+    // state
+    //-------------------------------------------------------------------
+
+   /**
+    * A map of context entry key name and context entry values.
+    */
+    private final Map m_map;
+
+   /**
+    * A map of the entry descriptors published by the component type
+    * and keyed by entry key.
+    */
+    private final Map m_entries = new Hashtable();
+
+   /**
+    * The component type.
+    */
+    private final Type m_type;
+
+    //-------------------------------------------------------------------
+    // constructor
+    //-------------------------------------------------------------------
+
+   /**
+    * Create a context invocation handler.
+    *
+    * @param type the component type
+    * @param map a map of context values keyed by entry key
+    */
+    public ContextInvocationHandler( Type type, Map map )
+        throws NullPointerException
+    {
+        assertNotNull( map, "map" );
+        assertNotNull( type, "type" );
+
+        m_map = map;
+        m_type = type;
+
+        EntryDescriptor[] entries = type.getContext().getEntries();
+        for( int i=0; i<entries.length; i++ )
+        {
+            EntryDescriptor p = entries[i];
+            String key = p.getKey();
+            boolean required = p.isRequired();
+            m_entries.put( key, p );
+            if( required && ( false == map.containsKey( key ) ) )
+            {
+                final String error = 
+                  "The component type ["
+                  + type.getInfo().getClassname() 
+                  + "] declares a required context entry under the key ["
+                  + key
+                  + "] however, no corresponding value has been supplied 
within the context map.";
+                throw new IllegalArgumentException( error );
+            }
+        }
+    }
+
+    //-------------------------------------------------------------------
+    // implementation
+    //-------------------------------------------------------------------
+
+   /**
+    * Invoke the specified method on underlying object.
+    * This is called by the proxy object.
+    *
+    * @param proxy the proxy object
+    * @param method the method invoked on proxy object
+    * @param args the arguments supplied to method
+    * @return the return value of method
+    * @throws Throwable if an error occurs
+    * @exception NullPointerException if any one of the proxy or method 
arguments
+    *            is null, or if the object instance has been destroyed 
earlier.
+    */
+    public Object invoke( final Object proxy, final Method method, final 
Object[] args )
+        throws Throwable, NullPointerException
+    {
+        if( proxy == null )
+          throw new NullPointerException( "proxy" );
+        if( method == null )
+          throw new NullPointerException( "method" );
+
+        String name = method.getName();
+        String key = getKeyFromMethod( method );
+        EntryDescriptor entry = (EntryDescriptor) m_entries.get( key );
+        
+        if( null == entry )
+        {
+            final String error =
+              "Illegal request for an undeclared context entry [" 
+              + key 
+              + "] withing the component type ["
+              + m_type.getInfo().getClassname()
+              + "].";
+            throw new IllegalArgumentException( error );               
+        }
+
+        //
+        // we have a valid key
+        //
+
+        Object value = m_map.get( key );
+        if( null != value )
+        {
+            return returnClientSuppliedDefaultArgument( entry, args );
+        }
+        else
+        {
+            return value;
+        }
+    }
+
+    private String getKeyFromMethod( Method method )
+    {
+        String name = method.getName();
+        if( name.startsWith( "get" ) )
+        {
+            return formatKey( name.substring( 3 ) );
+        }
+        else
+        {
+            final String error = 
+              "Invalid method accessor ["
+              + name 
+              + "]";
+            throw new IllegalArgumentException( error );
+        }
+    }
+
+    private String formatKey( String key )
+    {
+        if( key.length() < 1 ) 
+        {
+            throw new IllegalArgumentException( "key" );
+        }
+        String first = key.substring( 0, 1 ).toLowerCase();
+        String remainder = key.substring( 1 );
+        return first + remainder;
+    }
+
+    private Object returnClientSuppliedDefaultArgument( EntryDescriptor 
entry, Object[] args )
+    {
+        if( args.length < 1 )
+        {
+            final String error = 
+              "Insuffient arguments to resolve a default value for the key ["
+              + entry.getKey() 
+              + "] within the component type ["
+              + m_type.getInfo().getName() 
+              + "].";
+            throw new IllegalArgumentException( error );
+        }
+        Object arg = args[0];
+        return arg;
+    }
+
+    //-------------------------------------------------------------------
+    // implementation
+    //-------------------------------------------------------------------
+
+    private void assertNotNull( Object object, String key )
+        throws NullPointerException
+    {
+        if( null == object )
+        {
+            throw new NullPointerException( key );
+        }
+    }
+}