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Ajax4jsf is an open source extension to the JavaServer Faces standard that adds AJAX capability to JSF applications without requiring the writing of any JavaScript.
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/**
 * Copyright 2004 The Apache Software Foundation.
 *
 * 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 org.ajax4jsf.taglib.ajax;

import javax.faces.component.UIComponent;
import javax.faces.context.FacesContext;
import javax.faces.el.ReferenceSyntaxException;
import javax.faces.el.ValueBinding;
import javax.faces.webapp.UIComponentTag;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.Tag;
import javax.servlet.jsp.tagext.TagSupport;

import org.ajax4jsf.framework.ajax.AjaxListener;
import org.ajax4jsf.framework.ajax.AjaxListenerHelper;
import org.ajax4jsf.framework.ajax.AjaxSource;
import org.ajax4jsf.framework.util.message.Messages;


/**
 * @author shura
 * 
 * Custom tag for append AJAX request listeners to AjaxContainer.
 *  
 */
public class AjaxListenerTag extends TagSupport {

    /**
     * 
     */
    private static final long serialVersionUID = 2576519366310474212L;
    /**
     * class name for ajax events listener.   
     */
    private String type = null;
    
    private String binding = null;

    /**
     *  
     */
    public AjaxListenerTag() {
    }

    public void setType(String type) {
        this.type = type;
    }

    /**
	 * @param binding the binding to set
	 */
	public void setBinding(String binding) {
		this.binding = binding;
	}

	public int doStartTag() throws JspException {
        if (type == null) {
            throw new JspException(Messages.getMessage(Messages.NULL_TYPE_ATTRIBUTE_ERROR));
        }

        //Find parent UIComponentTag
        UIComponentTag componentTag = UIComponentTag
                .getParentUIComponentTag(pageContext);
        if (componentTag == null) {
            throw new JspException(
            		Messages.getMessage(Messages.NO_UI_COMPONENT_TAG_ANCESTOR_ERROR, "AjaxListenerTag"));
        }

        if (componentTag.getCreated()) {
            //Component was just created, so we add the Listener
            UIComponent component = componentTag.getComponentInstance();
            if (component instanceof AjaxSource) {
                AjaxListener listener;
                if(null != binding){
                	ValueBinding valueBinding;
                	try {
					valueBinding = FacesContext.getCurrentInstance().getApplication().createValueBinding(binding);
                	} catch (ReferenceSyntaxException e) {
						throw new JspException(e);
					}
                	listener = new AjaxListenerHelper(valueBinding);
                } else {
                String className;
                if (UIComponentTag.isValueReference(type)) {
                    FacesContext facesContext = FacesContext
                            .getCurrentInstance();
                    ValueBinding valueBinding = facesContext.getApplication()
                            .createValueBinding(type);
                    className = (String) valueBinding.getValue(facesContext);
                } else {
                    className = type;
                }
				try {
					listener = (AjaxListener) Class.forName(className).newInstance();
				} catch (Exception e) {
	                throw new JspException(Messages.getMessage(Messages.INSTANTIATE_LISTENER_ERROR, className, component.getId()), e);
				} 
                }
                ((AjaxSource) component).addAjaxListener(listener);
            } else {
                throw new JspException(Messages.getMessage(Messages.NOT_AJAX_CONTAINER_ERROR, component.getId()));
            }
        }

        return Tag.SKIP_BODY;
    }

}