vaadin-framework/server/src/main/java/com/vaadin/event/dd/acceptcriteria/ServerSideCriterion.java

/*
 * Copyright 2000-2016 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 com.vaadin.event.Transferable;
import com.vaadin.server.PaintException;
import com.vaadin.server.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}).
 * <p>
 * Subclasses should implement the
 * {@link AcceptCriterion#accept(com.vaadin.event.dd.DragAndDropEvent)} method.
 * <p>
 * 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 AcceptCriterion {

    private static final long serialVersionUID = 2128510128911628902L;

    @Override
    public final boolean isClientSideVerifiable() {
        return false;
    }

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

    public void paintContent(PaintTarget target) {
    }

    @Override
    public void paintResponse(PaintTarget target) throws PaintException {
    }

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