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Vaadin is a web application framework for Rich Internet Applications (RIA). Vaadin enables easy development and maintenance of fast and secure rich web applications with a stunning look and feel and a wide browser support. It features a server-side architecture with the majority of the logic running on the server. Ajax technology is used at the browser-side to ensure a rich and interactive user experience.

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/*
 * Copyright 2011 Vaadin Ltd.
 * 
 * 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 com.vaadin.event.dd.acceptcriteria;

import java.io.Serializable;

import com.vaadin.event.Transferable;
import com.vaadin.terminal.PaintException;
import com.vaadin.terminal.PaintTarget;

/**
 * Parent class for criteria which are verified on the server side during a drag
 * operation to accept/discard dragged content (presented by
 * {@link Transferable}).
 * 
 * Subclasses should implement the
 * {@link AcceptCriterion#accept(com.vaadin.event.dd.DragAndDropEvent)} method.
 * 
 * As all server side state can be used to make a decision, this is more
 * flexible than {@link ClientSideCriterion}. However, this does require
 * additional requests from the browser to the server during a drag operation.
 * 
 * @see AcceptCriterion
 * @see ClientSideCriterion
 * 
 * @since 6.3
 */
public abstract class ServerSideCriterion implements Serializable,
        AcceptCriterion {

    private static final long serialVersionUID = 2128510128911628902L;

    public final boolean isClientSideVerifiable() {
        return false;
    }

    public void paint(PaintTarget target) throws PaintException {
        target.startTag("-ac");
        target.addAttribute("name", getIdentifier());
        paintContent(target);
        target.endTag("-ac");
    }

    public void paintContent(PaintTarget target) {
    }

    public void paintResponse(PaintTarget target) throws PaintException {
    }

    protected String getIdentifier() {
        return ServerSideCriterion.class.getCanonicalName();
    }
}