myfaces-html5-core/src/main/java/org/apache/myfaces/html5/handler/DropTargetBehaviorHandler.java - myfaces-html5 - Git at Google

 /*
  * Licensed to the Apache Software Foundation (ASF) under one
  * or more contributor license agreements.  See the NOTICE file
  * distributed with this work for additional information
  * regarding copyright ownership.  The ASF licenses this file
  * to you 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 org.apache.myfaces.html5.handler;

 import java.util.Collection;
 import java.util.logging.Level;
 import java.util.logging.Logger;

 import javax.el.MethodExpression;
 import javax.faces.FacesException;
 import javax.faces.application.Application;
 import javax.faces.component.UIComponent;
 import javax.faces.component.behavior.Behavior;
 import javax.faces.component.behavior.ClientBehaviorHolder;
 import javax.faces.context.FacesContext;
 import javax.faces.view.facelets.BehaviorConfig;
 import javax.faces.view.facelets.ComponentHandler;
 import javax.faces.view.facelets.FaceletContext;
 import javax.faces.view.facelets.TagAttribute;
 import javax.faces.view.facelets.TagException;

 import org.apache.myfaces.buildtools.maven2.plugin.builder.annotation.JSFFaceletAttribute;
 import org.apache.myfaces.buildtools.maven2.plugin.builder.annotation.JSFFaceletTag;
 import org.apache.myfaces.html5.behavior.DropTargetBehavior;
 import org.apache.myfaces.html5.component.util.ComponentUtils;
 import org.apache.myfaces.html5.event.DropEvent;
 import org.apache.myfaces.html5.event.DropListener;
 import org.apache.myfaces.html5.renderkit.behavior.DropTargetBehaviorRenderer;
 import org.apache.myfaces.html5.renderkit.util.ClientBehaviorEvents;

 /*
  * Facelets tag handler for DropTargetBehavior.
  *
  *
  * DO NOT JAVADOC here since we don't want this doc to show up in Facelets doc.
  */
 @JSFFaceletTag(name = "fx:dropTarget", behaviorClass="org.apache.myfaces.html5.behavior.DropTargetBehavior")
 public class DropTargetBehaviorHandler extends javax.faces.view.facelets.BehaviorHandler
 {

     private static final Logger log = Logger.getLogger(DropTargetBehaviorHandler.class.getName());

     /**
      * Action to allow for drop operation. Can be one of below:
      * <ul>
      * <li>copy: A copy of the source item may be made at the new location.</li>
      * <li>move: An item may be moved to a new location.</li>
      * <li>link: A link may be established to the source at the new location.</li>
      * <li>copyLink: A copy or link operation is permitted.</li>
      * <li>copyMove: A copy or move operation is permitted.</li>
      * <li>linkMove: A link or move operation is permitted.</li>
      * <li>all: All operations are permitted.</li>
      * <li>none: The item may not be dropped.</li>
      * </ul>
      * <br/>
      *
      * If nothing is specified, any action will be accepted. Action is set by the hx:dragSource behavior, when the
      * element is generated by a MyFaces-Html5 component that has hx:dragSource behavior. For other elements, action is
      * set by the browser, and can be adjusted by pressing the modifier keys.
      *
      */
     @JSFFaceletAttribute(name = "action", className = "javax.el.ValueExpression", deferredValueType = "java.lang.String")
     private final TagAttribute _action;

     /**
      * The type of the drop target. Can be comma separated set or String[] or Collection&lt;String&gt;. <br/>
      * If defined, drags from elements that are generated by MyFaces-Html5 components with hx:dragSource behavior, will
      * be filtered. The drag will be accepted if dropTargetTypes of hx:dragSource is one of the allowed. For the drags
      * that are originated from other elements, this property is ignored. Please see acceptMimeTypes property for
      * accepting/rejecting drags from non-MyFaces-Html5 components.
      */
     @JSFFaceletAttribute(name = "types", className = "javax.el.ValueExpression", deferredValueType = "java.lang.Object")
     private final TagAttribute _types;

     /**
      * If this property is set, only content dropped into this drop zone with defined mime type will be accepted and
      * sent to server-side drop listener. Can be comma separated set or String[] or Collection&lt;String&gt;. <br/>
      * <br/>
      * HTML5 DnD allows us to drop anything into drop zone : files from desktop, images on some other document, etc. So
      * this property is a filter. If value is "*", any content dropped into this zone will be accepted. <br/>
      * <br/>
      * All type info and data of dropped stuff will be sent to dropListener. For example, if value of this property is
      * "*" and we drop some image from any Html page(even not generated by JSF), dropListener will be triggered with the
      * following data:
      * <code>
      * &lt;table border="1"&gt;
      * &lt;tr&gt;
      * &lt;td&gt;content-type&lt;/td&gt;
      * &lt;td&gt;value&lt;/td&gt;
      * &lt;/tr&gt;
      * &lt;tr&gt;
      * &lt;td&gt;text/uri-list&lt;/td&gt;
      * &lt;td&gt;http://example.org/someImage.png&lt;/td&gt;
      * &lt;/tr&gt;
      * &lt;tr&gt;
      * &lt;td&gt;Text&lt;/td&gt;
      * &lt;td&gt;http://example.org/someImage.png&lt;/td&gt;
      * &lt;/tr&gt;
      * &lt;tr&gt;
      * &lt;td&gt;text/plain&lt;/td&gt;
      * &lt;td&gt;http://example.org/someImage.png&lt;/td&gt;
      * &lt;/tr&gt;
      * &lt;tr&gt;
      * &lt;td&gt;URL&lt;/td&gt;
      * &lt;td&gt;http://example.org/someImage.png&lt;/td&gt;
      * &lt;/tr&gt;
      * &lt;/table&gt;
      * </code>
      * <br/>
      *
      * Mime type is "text/x-myfaces-html5-dnd-source" for drag and drop events that is generated by MyFaces-Html5 components
      * and that mime type is defined at {@link DropTargetBehaviorRenderer#DEFAULT_MYFACES_MIME_TYPE}. Default value of
      * this property is "text/x-myfaces-html5-dnd-source", thus only MyFaces generated components can be dropped into
      * the drop target.
      */
     @JSFFaceletAttribute(name = "acceptMimeTypes", className = "javax.el.ValueExpression", deferredValueType = "java.lang.Object")
     private final TagAttribute _acceptMimeTypes;

     /**
      * Space separated ids of components to rerender. <br/>
      * Value of this property will be passed through to jsf.ajax.request, thus semantics is same with jsf.ajax.request
      * and f:ajax. Just like those, @all, @this etc. can be used.
      */
     @JSFFaceletAttribute(name = "rerender", className = "javax.el.ValueExpression", deferredValueType = "java.lang.Object")
     private final TagAttribute _rerender;

     /**
      * Drop listener to trigger when a successful drop event is happened into this drop target. <br/>
      * Listener method must have a signature of :
      * <code>public void m(org.apache.myfaces.html5.event.DropEvent evt) throws javax.faces.event.AbortProcessingException</code>
      * <br/>
      * In the listener, application can get the parameter sent and other data sent.
      */
     @JSFFaceletAttribute(name = "dropListener", className = "javax.el.MethodExpression", deferredMethodSignature = "public void m(org.apache.myfaces.html5.event.DropEvent evt) throws javax.faces.event.AbortProcessingException")
     private final TagAttribute _dropListener;

     public DropTargetBehaviorHandler(BehaviorConfig config)
     {
         super(config);
         _action = getAttribute("action");
         _types = getAttribute("types");
         _acceptMimeTypes = getAttribute("acceptMimeTypes");
         _rerender = getAttribute("rerender");
         _dropListener = getAttribute("dropListener");
     }

     @Override
     public void apply(FaceletContext faceletContext, UIComponent parent)
     {
         if (!ComponentHandler.isNew(parent))
         {
             if (log.isLoggable(Level.FINE))
                 log.fine("Component" + ComponentUtils.getPathToComponent(parent)
                         + " is not new, thus return without any operation.");
             return;
         }

         if (parent instanceof ClientBehaviorHolder)
         {
             ClientBehaviorHolder holder = _getClientBehaviorHolder(parent);

             FacesContext context = faceletContext.getFacesContext();
             Application app = context.getApplication();
             String behaviorId = getBehaviorId();
             Behavior behavior = app.createBehavior(behaviorId);

             if (!(behavior instanceof DropTargetBehavior))
             {
                 throw new FacesException("Behavior is not a DropTargetBehavior");
             }

             // manually added all of the properties, so no need for this:
             // setAttributes(faceletContext, behavior);

             DropTargetBehavior dropTargetBehavior = (DropTargetBehavior) behavior;

             if (_dropListener != null)
             {

                 MethodExpression expr = _dropListener.getMethodExpression(faceletContext, Void.TYPE, new Class<?>[]
                 {
                     DropEvent.class
                 });
                 dropTargetBehavior.addDropTargetBehaviorListener(new DropListener(expr));
             }

             // see https://issues.apache.org/jira/browse/MYFACES-2616
             // see the thread http://www.mail-archive.com/dev@myfaces.apache.org/msg46764.html
             // using the same approach in DropSourceBehavior too... see there for explanation!
             if (_action != null)
             {
                 if (_action.isLiteral())
                 {
                     dropTargetBehavior.setAction(_action.getValue(faceletContext));
                 }
                 else
                 {
                     dropTargetBehavior.setValueExpression("action", _action.getValueExpression(faceletContext,
                             String.class));
                 }
             }
             if (_types != null)
             {
                 if (_types.isLiteral())
                 {
                     dropTargetBehavior.setTypes(_types.getObject(faceletContext));
                 }
                 else
                 {
                     dropTargetBehavior.setValueExpression("types", _types.getValueExpression(faceletContext,
                             Object.class));
                 }
             }
             if (_acceptMimeTypes != null)
             {
                 if (_acceptMimeTypes.isLiteral())
                 {
                     dropTargetBehavior.setAcceptMimeTypes(_acceptMimeTypes.getObject(faceletContext));
                 }
                 else
                 {
                     dropTargetBehavior.setValueExpression("acceptMimeTypes", _acceptMimeTypes.getValueExpression(
                             faceletContext, Object.class));
                 }
             }
             if (_rerender != null)
             {
                 if (_rerender.isLiteral())
                 {
                     dropTargetBehavior.setRerender(_rerender.getObject(faceletContext));
                 }
                 else
                 {
                     dropTargetBehavior.setValueExpression("rerender", _rerender.getValueExpression(faceletContext,
                             Object.class));
                 }
             }

             holder.addClientBehavior(ClientBehaviorEvents.DRAGENTER_EVENT, dropTargetBehavior);
             holder.addClientBehavior(ClientBehaviorEvents.DRAGOVER_EVENT, dropTargetBehavior);
             holder.addClientBehavior(ClientBehaviorEvents.DROP_EVENT, dropTargetBehavior);
         }
         //XXX: try in a composite component!
         /*
          * else if (UIComponent.isCompositeComponent(parent)) { // COPIED FROM AjaxHandler! // It is supposed that for
          * composite components, this tag should // add itself as a target, but note that on whole api does not exists
          * // some tag that expose client behaviors as targets for composite // components. In RI, there exists a tag
          * called composite:clientBehavior, // but does not appear on spec or javadoc, maybe because this could be //
          * understand as an implementation detail, after all there exists a key // called
          * AttachedObjectTarget.ATTACHED_OBJECT_TARGETS_KEY that could be // used to create a tag outside jsf
          * implementation to attach targets. CompositeComponentResourceTagHandler.addAttachedObjectHandler(parent,
          * this); }
          */
     }

     private ClientBehaviorHolder _getClientBehaviorHolder(UIComponent parent)
     {
         if (!(parent instanceof ClientBehaviorHolder))
         {
             throw new TagException(getTag(),
                     "DropTargetBehavior must be attached to a ClientBehaviorHolder parent. Component "
                             + ComponentUtils.getPathToComponent(parent) + "is not a ClientBehaviorHolder");
         }

         ClientBehaviorHolder holder = (ClientBehaviorHolder) parent;

         _checkEvent(holder, ClientBehaviorEvents.DRAGENTER_EVENT);
         _checkEvent(holder, ClientBehaviorEvents.DRAGOVER_EVENT);
         _checkEvent(holder, ClientBehaviorEvents.DROP_EVENT);

         return holder;
     }

     private void _checkEvent(ClientBehaviorHolder holder, String eventName)
     {
         Collection<String> eventNames = holder.getEventNames();

         if (!eventNames.contains(eventName))
         {
             StringBuilder message = new StringBuilder();
             message.append("Unable to attach DropTargetBehavior.  ");
             message.append("DropTargetBehavior may only be attached to ");
             message.append("ClientBehaviorHolders that support the '");
             message.append(eventName);
             message.append("' event.  The parent ClientBehaviorHolder "
                     + ComponentUtils.getPathToComponent((UIComponent) holder) + " only ");
             message.append("supports the following events: ");

             for (String supportedEventName : eventNames)
             {
                 message.append(supportedEventName);
                 message.append(" ");
             }

             throw new TagException(getTag(), message.toString());
         }
     }

 }
	/*
	* Licensed to the Apache Software Foundation (ASF) under one
	* or more contributor license agreements. See the NOTICE file
	* distributed with this work for additional information
	* regarding copyright ownership. The ASF licenses this file
	* to you 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 org.apache.myfaces.html5.handler;

	import java.util.Collection;
	import java.util.logging.Level;
	import java.util.logging.Logger;

	import javax.el.MethodExpression;
	import javax.faces.FacesException;
	import javax.faces.application.Application;
	import javax.faces.component.UIComponent;
	import javax.faces.component.behavior.Behavior;
	import javax.faces.component.behavior.ClientBehaviorHolder;
	import javax.faces.context.FacesContext;
	import javax.faces.view.facelets.BehaviorConfig;
	import javax.faces.view.facelets.ComponentHandler;
	import javax.faces.view.facelets.FaceletContext;
	import javax.faces.view.facelets.TagAttribute;
	import javax.faces.view.facelets.TagException;

	import org.apache.myfaces.buildtools.maven2.plugin.builder.annotation.JSFFaceletAttribute;
	import org.apache.myfaces.buildtools.maven2.plugin.builder.annotation.JSFFaceletTag;
	import org.apache.myfaces.html5.behavior.DropTargetBehavior;
	import org.apache.myfaces.html5.component.util.ComponentUtils;
	import org.apache.myfaces.html5.event.DropEvent;
	import org.apache.myfaces.html5.event.DropListener;
	import org.apache.myfaces.html5.renderkit.behavior.DropTargetBehaviorRenderer;
	import org.apache.myfaces.html5.renderkit.util.ClientBehaviorEvents;

	/*
	* Facelets tag handler for DropTargetBehavior.
	*
	*
	* DO NOT JAVADOC here since we don't want this doc to show up in Facelets doc.
	*/
	@JSFFaceletTag(name = "fx:dropTarget", behaviorClass="org.apache.myfaces.html5.behavior.DropTargetBehavior")
	public class DropTargetBehaviorHandler extends javax.faces.view.facelets.BehaviorHandler
	{

	private static final Logger log = Logger.getLogger(DropTargetBehaviorHandler.class.getName());

	/**
	* Action to allow for drop operation. Can be one of below:
	* <ul>
	* <li>copy: A copy of the source item may be made at the new location.</li>
	* <li>move: An item may be moved to a new location.</li>
	* <li>link: A link may be established to the source at the new location.</li>
	* <li>copyLink: A copy or link operation is permitted.</li>
	* <li>copyMove: A copy or move operation is permitted.</li>
	* <li>linkMove: A link or move operation is permitted.</li>
	* <li>all: All operations are permitted.</li>
	* <li>none: The item may not be dropped.</li>
	* </ul>
	* <br/>
	*
	* If nothing is specified, any action will be accepted. Action is set by the hx:dragSource behavior, when the
	* element is generated by a MyFaces-Html5 component that has hx:dragSource behavior. For other elements, action is
	* set by the browser, and can be adjusted by pressing the modifier keys.
	*
	*/
	@JSFFaceletAttribute(name = "action", className = "javax.el.ValueExpression", deferredValueType = "java.lang.String")
	private final TagAttribute _action;

	/**
	* The type of the drop target. Can be comma separated set or String[] or Collection<String>. <br/>
	* If defined, drags from elements that are generated by MyFaces-Html5 components with hx:dragSource behavior, will
	* be filtered. The drag will be accepted if dropTargetTypes of hx:dragSource is one of the allowed. For the drags
	* that are originated from other elements, this property is ignored. Please see acceptMimeTypes property for
	* accepting/rejecting drags from non-MyFaces-Html5 components.
	*/
	@JSFFaceletAttribute(name = "types", className = "javax.el.ValueExpression", deferredValueType = "java.lang.Object")
	private final TagAttribute _types;

	/**
	* If this property is set, only content dropped into this drop zone with defined mime type will be accepted and
	* sent to server-side drop listener. Can be comma separated set or String[] or Collection<String>. <br/>
	* <br/>
	* HTML5 DnD allows us to drop anything into drop zone : files from desktop, images on some other document, etc. So
	* this property is a filter. If value is "*", any content dropped into this zone will be accepted. <br/>
	* <br/>
	* All type info and data of dropped stuff will be sent to dropListener. For example, if value of this property is
	* "*" and we drop some image from any Html page(even not generated by JSF), dropListener will be triggered with the
	* following data:
	* <code>
	* <table border="1">
	* <tr>
	* <td>content-type</td>
	* <td>value</td>
	* </tr>
	* <tr>
	* <td>text/uri-list</td>
	* <td>http://example.org/someImage.png</td>
	* </tr>
	* <tr>
	* <td>Text</td>
	* <td>http://example.org/someImage.png</td>
	* </tr>
	* <tr>
	* <td>text/plain</td>
	* <td>http://example.org/someImage.png</td>
	* </tr>
	* <tr>
	* <td>URL</td>
	* <td>http://example.org/someImage.png</td>
	* </tr>
	* </table>
	* </code>
	* <br/>
	*
	* Mime type is "text/x-myfaces-html5-dnd-source" for drag and drop events that is generated by MyFaces-Html5 components
	* and that mime type is defined at {@link DropTargetBehaviorRenderer#DEFAULT_MYFACES_MIME_TYPE}. Default value of
	* this property is "text/x-myfaces-html5-dnd-source", thus only MyFaces generated components can be dropped into
	* the drop target.
	*/
	@JSFFaceletAttribute(name = "acceptMimeTypes", className = "javax.el.ValueExpression", deferredValueType = "java.lang.Object")
	private final TagAttribute _acceptMimeTypes;

	/**
	* Space separated ids of components to rerender. <br/>
	* Value of this property will be passed through to jsf.ajax.request, thus semantics is same with jsf.ajax.request
	* and f:ajax. Just like those, @all, @this etc. can be used.
	*/
	@JSFFaceletAttribute(name = "rerender", className = "javax.el.ValueExpression", deferredValueType = "java.lang.Object")
	private final TagAttribute _rerender;

	/**
	* Drop listener to trigger when a successful drop event is happened into this drop target. <br/>
	* Listener method must have a signature of :
	* <code>public void m(org.apache.myfaces.html5.event.DropEvent evt) throws javax.faces.event.AbortProcessingException</code>
	* <br/>
	* In the listener, application can get the parameter sent and other data sent.
	*/
	@JSFFaceletAttribute(name = "dropListener", className = "javax.el.MethodExpression", deferredMethodSignature = "public void m(org.apache.myfaces.html5.event.DropEvent evt) throws javax.faces.event.AbortProcessingException")
	private final TagAttribute _dropListener;

	public DropTargetBehaviorHandler(BehaviorConfig config)
	{
	super(config);
	_action = getAttribute("action");
	_types = getAttribute("types");
	_acceptMimeTypes = getAttribute("acceptMimeTypes");
	_rerender = getAttribute("rerender");
	_dropListener = getAttribute("dropListener");
	}

	@Override
	public void apply(FaceletContext faceletContext, UIComponent parent)
	{
	if (!ComponentHandler.isNew(parent))
	{
	if (log.isLoggable(Level.FINE))
	log.fine("Component" + ComponentUtils.getPathToComponent(parent)
	+ " is not new, thus return without any operation.");
	return;
	}

	if (parent instanceof ClientBehaviorHolder)
	{
	ClientBehaviorHolder holder = _getClientBehaviorHolder(parent);

	FacesContext context = faceletContext.getFacesContext();
	Application app = context.getApplication();
	String behaviorId = getBehaviorId();
	Behavior behavior = app.createBehavior(behaviorId);

	if (!(behavior instanceof DropTargetBehavior))
	{
	throw new FacesException("Behavior is not a DropTargetBehavior");
	}

	// manually added all of the properties, so no need for this:
	// setAttributes(faceletContext, behavior);

	DropTargetBehavior dropTargetBehavior = (DropTargetBehavior) behavior;

	if (_dropListener != null)
	{

	MethodExpression expr = _dropListener.getMethodExpression(faceletContext, Void.TYPE, new Class<?>[]
	{
	DropEvent.class
	});
	dropTargetBehavior.addDropTargetBehaviorListener(new DropListener(expr));
	}

	// see https://issues.apache.org/jira/browse/MYFACES-2616
	// see the thread http://www.mail-archive.com/dev@myfaces.apache.org/msg46764.html
	// using the same approach in DropSourceBehavior too... see there for explanation!
	if (_action != null)
	{
	if (_action.isLiteral())
	{
	dropTargetBehavior.setAction(_action.getValue(faceletContext));
	}
	else
	{
	dropTargetBehavior.setValueExpression("action", _action.getValueExpression(faceletContext,
	String.class));
	}
	}
	if (_types != null)
	{
	if (_types.isLiteral())
	{
	dropTargetBehavior.setTypes(_types.getObject(faceletContext));
	}
	else
	{
	dropTargetBehavior.setValueExpression("types", _types.getValueExpression(faceletContext,
	Object.class));
	}
	}
	if (_acceptMimeTypes != null)
	{
	if (_acceptMimeTypes.isLiteral())
	{
	dropTargetBehavior.setAcceptMimeTypes(_acceptMimeTypes.getObject(faceletContext));
	}
	else
	{
	dropTargetBehavior.setValueExpression("acceptMimeTypes", _acceptMimeTypes.getValueExpression(
	faceletContext, Object.class));
	}
	}
	if (_rerender != null)
	{
	if (_rerender.isLiteral())
	{
	dropTargetBehavior.setRerender(_rerender.getObject(faceletContext));
	}
	else
	{
	dropTargetBehavior.setValueExpression("rerender", _rerender.getValueExpression(faceletContext,
	Object.class));
	}
	}

	holder.addClientBehavior(ClientBehaviorEvents.DRAGENTER_EVENT, dropTargetBehavior);
	holder.addClientBehavior(ClientBehaviorEvents.DRAGOVER_EVENT, dropTargetBehavior);
	holder.addClientBehavior(ClientBehaviorEvents.DROP_EVENT, dropTargetBehavior);
	}
	//XXX: try in a composite component!
	/*
	* else if (UIComponent.isCompositeComponent(parent)) { // COPIED FROM AjaxHandler! // It is supposed that for
	* composite components, this tag should // add itself as a target, but note that on whole api does not exists
	* // some tag that expose client behaviors as targets for composite // components. In RI, there exists a tag
	* called composite:clientBehavior, // but does not appear on spec or javadoc, maybe because this could be //
	* understand as an implementation detail, after all there exists a key // called
	* AttachedObjectTarget.ATTACHED_OBJECT_TARGETS_KEY that could be // used to create a tag outside jsf
	* implementation to attach targets. CompositeComponentResourceTagHandler.addAttachedObjectHandler(parent,
	* this); }
	*/
	}

	private ClientBehaviorHolder _getClientBehaviorHolder(UIComponent parent)
	{
	if (!(parent instanceof ClientBehaviorHolder))
	{
	throw new TagException(getTag(),
	"DropTargetBehavior must be attached to a ClientBehaviorHolder parent. Component "
	+ ComponentUtils.getPathToComponent(parent) + "is not a ClientBehaviorHolder");
	}

	ClientBehaviorHolder holder = (ClientBehaviorHolder) parent;

	_checkEvent(holder, ClientBehaviorEvents.DRAGENTER_EVENT);
	_checkEvent(holder, ClientBehaviorEvents.DRAGOVER_EVENT);
	_checkEvent(holder, ClientBehaviorEvents.DROP_EVENT);

	return holder;
	}

	private void _checkEvent(ClientBehaviorHolder holder, String eventName)
	{
	Collection<String> eventNames = holder.getEventNames();

	if (!eventNames.contains(eventName))
	{
	StringBuilder message = new StringBuilder();
	message.append("Unable to attach DropTargetBehavior. ");
	message.append("DropTargetBehavior may only be attached to ");
	message.append("ClientBehaviorHolders that support the '");
	message.append(eventName);
	message.append("' event. The parent ClientBehaviorHolder "
	+ ComponentUtils.getPathToComponent((UIComponent) holder) + " only ");
	message.append("supports the following events: ");

	for (String supportedEventName : eventNames)
	{
	message.append(supportedEventName);
	message.append(" ");
	}

	throw new TagException(getTag(), message.toString());
	}
	}

	}