Content of file LocalTransfer.java

/**
 * Copyright (c) 2002-2006 IBM Corporation and others.
 * 
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 * IBM - Initial API and implementation
 */
// REUSED CLASS
package org.eclipse.emf.edit.ui.dnd;

import org.eclipse.swt.dnd.ByteArrayTransfer;
import org.eclipse.swt.dnd.TransferData;

/**
 * This derived implementation of a byte array transfer short circuits the transfer process
 * so that a local transfer does not serialize the object
 * and hence can and will return the original object, not just a clone.
 * You only really need ever know about {@link #getInstance LocalTransfer.getInstance()},
 * so that you can include it in when adding drag support to a viewer.
 * See {@link EditingDomainViewerDropAdapter} and {@link ViewerDragAdapter} for more details.
 * <p>
 * As an added guard, the time is recorded and serialized in javaToNative to that native to java can ensure that it's
 * returns the value that was really to have been transferred.
 */
public class LocalTransfer extends ByteArrayTransfer {
	private static final long serialVersionUID = 1L;

	/**
	 * This is the register transfer type name.
	 */
	protected static final String TYPE_NAME = "local-transfer-format";

	/**
	 * This is the ID that is registered to the name.
	 */
	protected static final int TYPE_ID = registerType(TYPE_NAME);

	/**
	 * This is initialized and returned by {@link #getInstance}.
	 */
	protected static LocalTransfer instance;

	/**
	 * This returns the one instance of this transfer agent.
	 */
	public static LocalTransfer getInstance() {
		if (instance == null) {
			instance = new LocalTransfer();
		}

		return instance;
	}

	/**
	 * This records the time at which the transfer data was recorded.
	 */
	protected long startTime;

	/**
	 * This records the data being transferred.
	 */
	protected Object object;

	/**
	 * This creates an instance; typically you get one from {@link #getInstance}.
	 */
	protected LocalTransfer() {
		super();
	}

	/**
	 * This returns the transfer IDs that this agent supports.
	 */
	@Override
	protected int[] getTypeIds() {
		return new int[] { TYPE_ID };
	}

	/**
	 * This returns the transfer names that this agent supports.
	 */
	@Override
	public String[] getTypeNames() {
		return new String[] { TYPE_NAME };
	}

	/**
	 * This records the object and current time and encodes only the current time into the transfer data.
	 */
	@Override
	public void javaToNative(Object object, TransferData transferData) {
		startTime = System.currentTimeMillis();
		this.object = object;
		if (transferData != null) {
			super.javaToNative(String.valueOf(startTime).getBytes(), transferData);
		}
	}

	/**
	 * This decodes the time of the transfer and returns the recorded the object if the recorded time and the decoded
	 * time match.
	 */
	@Override
	public Object nativeToJava(TransferData transferData) {
		final byte[] bytes = (byte[]) super.nativeToJava(transferData);
		if (bytes == null) {
			return null;
		}

		try {
			final long startTime = Long.parseLong(new String(bytes));
			return this.startTime == startTime ? object : null;
		} catch (final NumberFormatException exception) {
			return null;
		}
	}
}