MarkerTransfer.java

/*******************************************************************************
 * Copyright (c) 2000, 2008 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/

package org.eclipse.ui.part;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;

import org.eclipse.core.resources.IMarker;
import org.eclipse.core.resources.IResource;
import org.eclipse.core.resources.IWorkspace;
import org.eclipse.core.runtime.IPath;
import org.eclipse.core.runtime.Path;
import org.eclipse.swt.dnd.ByteArrayTransfer;
import org.eclipse.swt.dnd.TransferData;

/**
 * A <code>MarkerTransfer</code> is used to transfer an array of 
 * <code>IMarker</code>s from one part to another in a drag and drop 
 * operation.
 * <p>
 * In every drag and drop operation there is a <code>DragSource</code> and 
 * a <code>DropTarget</code>.  When a drag occurs a <code>Transfer</code> is 
 * used to marshall the drag data from the source into a byte array.  If a drop 
 * occurs another <code>Transfer</code> is used to marshall the byte array into
 * drop data for the target.
 * </p><p>
 * This class can be used for a <code>Viewer<code> or an SWT component directly.
 * A singleton is provided which may be serially reused (see <code>getInstance</code>).  
 * It is not intended to be subclassed.
 * </p>
 *
 * @see org.eclipse.jface.viewers.StructuredViewer
 * @see org.eclipse.swt.dnd.DropTarget
 * @see org.eclipse.swt.dnd.DragSource
 * @noextend This class is not intended to be subclassed by clients.
 */
public class MarkerTransfer extends ByteArrayTransfer {

    /**
     * Singleton instance.
     */
    private static final MarkerTransfer instance = new MarkerTransfer();

    // Create a unique ID to make sure that different Eclipse
    // applications use different "types" of <code>MarkerTransfer</code>
    private static final String TYPE_NAME = "marker-transfer-format" + System.currentTimeMillis() + ":" + instance.hashCode();//$NON-NLS-2$//$NON-NLS-1$

    private static final int TYPEID = registerType(TYPE_NAME);

    private IWorkspace workspace;

    /**
     * Creates a new transfer object.
     */
    private MarkerTransfer() {
    }

    /**
     * Locates and returns the marker associated with the given attributes.
     *
     * @param pathString the resource path
     * @param id the id of the marker to get (as per {@link IResource#getMarker
     *    IResource.getMarker})
     * @return the specified marker
     */
    private IMarker findMarker(String pathString, long id) {
        IPath path = new Path(pathString);
        IResource resource = workspace.getRoot().findMember(path);
        if (resource != null) {
            return resource.getMarker(id);
        }
        return null;
    }

    /**
     * Returns the singleton instance.
     *
     * @return the singleton instance
     */
    public static MarkerTransfer getInstance() {
        return instance;
    }

    /* (non-Javadoc)
     * Method declared on Transfer.
     */
    protected int[] getTypeIds() {
        return new int[] { TYPEID };
    }

    /* (non-Javadoc)
     * Returns the type names.
     *
     * @return the list of type names
     */
    protected String[] getTypeNames() {
        return new String[] { TYPE_NAME };
    }

    /* (non-Javadoc)
     * Method declared on Transfer.
     * On a successful conversion, the transferData.result field will be set to
     * OLE.S_OK. If this transfer agent is unable to perform the conversion, the
     * transferData.result field will be set to the failure value of OLE.DV_E_TYMED.
     */
    protected void javaToNative(Object object, TransferData transferData) {
        /**
         * Transfer data is an array of markers.  Serialized version is:
         * (int) number of markers
         * (Marker) marker 1
         * (Marker) marker 2
         * ... repeat last four for each subsequent marker
         * see writeMarker for the (Marker) format.
         */
        Object[] markers = (Object[]) object;
        lazyInit(markers);

        ByteArrayOutputStream byteOut = new ByteArrayOutputStream();
        DataOutputStream out = new DataOutputStream(byteOut);

        byte[] bytes = null;

        try {
            /* write number of markers */
            out.writeInt(markers.length);

            /* write markers */
            for (int i = 0; i < markers.length; i++) {
                writeMarker((IMarker) markers[i], out);
            }
            out.close();
            bytes = byteOut.toByteArray();
        } catch (IOException e) {
            //when in doubt send nothing
        }

        if (bytes != null) {
            super.javaToNative(bytes, transferData);
        }
    }

    /**
     * Initializes the transfer mechanism if necessary.
     */
    private void lazyInit(Object[] markers) {
        if (workspace == null) {
            if (markers != null && markers.length > 0) {
                this.workspace = ((IMarker) markers[0]).getResource()
                        .getWorkspace();
            }
        }
    }

    /* (non-Javadoc)
     * Method declared on Transfer.
     */
    protected Object nativeToJava(TransferData transferData) {
        byte[] bytes = (byte[]) super.nativeToJava(transferData);
        DataInputStream in = new DataInputStream(
                new ByteArrayInputStream(bytes));

        try {
            /* read number of markers */
            int n = in.readInt();

            /* read markers */
            IMarker[] markers = new IMarker[n];
            for (int i = 0; i < n; i++) {
                IMarker marker = readMarker(in);
                if (marker == null) {
                    return null;
                }
                markers[i] = marker;
            }
            return markers;
        } catch (IOException e) {
            return null;
        }
    }

    /**
     * Reads and returns a single marker from the given stream.
     *
     * @param dataIn the input stream
     * @return the marker
     * @exception IOException if there is a problem reading from the stream
     */
    private IMarker readMarker(DataInputStream dataIn) throws IOException {
        /**
         * Marker serialization format is as follows:
         * (String) path of resource for marker
         * (int) marker ID
         */
        String path = dataIn.readUTF();
        long id = dataIn.readLong();
        return findMarker(path, id);
    }

    /**
     * Writes the given marker to the given stream.
     *
     * @param marker the marker
     * @param dataOut the output stream
     * @exception IOException if there is a problem writing to the stream
     */
    private void writeMarker(IMarker marker, DataOutputStream dataOut)
            throws IOException {
        /**
         * Marker serialization format is as follows:
         * (String) path of resource for marker
         * (int) marker ID
         */

        dataOut.writeUTF(marker.getResource().getFullPath().toString());
        dataOut.writeLong(marker.getId());
    }
}