org.eclipse.swt.dnd.ByteArrayTransfer.java Source code

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Here is the source code for org.eclipse.swt.dnd.ByteArrayTransfer.java

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/*******************************************************************************
 * 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.swt.dnd;

/**
 * The class <code>ByteArrayTransfer</code> provides a platform specific 
 * mechanism for converting a java <code>byte[]</code> to a platform 
 * specific representation of the byte array and vice versa.
 *
 * <p><code>ByteArrayTransfer</code> is never used directly but is sub-classed 
 * by transfer agents that convert between data in a java format such as a
 * <code>String</code> and a platform specific byte array.
 * 
 * <p>If the data you are converting <b>does not</b> map to a 
 * <code>byte[]</code>, you should sub-class <code>Transfer</code> directly 
 * and do your own mapping to a platform data type.</p>
 * 
 * <p>The following snippet shows a subclass of ByteArrayTransfer that transfers
 * data defined by the class <code>MyType</code>.</p>
 * 
 * <pre><code>
 * public class MyType {
 *   public String fileName;
 *   public long fileLength;
 *   public long lastModified;
 * }
 * </code></pre>
 * 
 * <pre><code>
 * public class MyTypeTransfer extends ByteArrayTransfer {
 *   
 *   private static final String MYTYPENAME = "my_type_name";
 *   private static final int MYTYPEID = registerType(MYTYPENAME);
 *   private static MyTypeTransfer _instance = new MyTypeTransfer();
 * 
 * private MyTypeTransfer() {}
 * 
 * public static MyTypeTransfer getInstance () {
 *    return _instance;
 * }
 * public void javaToNative (Object object, TransferData transferData) {
 *    if (object == null || !(object instanceof MyType[])) return;
 *    
 *    if (isSupportedType(transferData)) {
 *       MyType[] myTypes = (MyType[]) object;   
 *       try {
 *          // write data to a byte array and then ask super to convert to pMedium
 *          ByteArrayOutputStream out = new ByteArrayOutputStream();
 *          DataOutputStream writeOut = new DataOutputStream(out);
 *          for (int i = 0, length = myTypes.length; i &lt; length;  i++){
 *             byte[] buffer = myTypes[i].fileName.getBytes();
 *             writeOut.writeInt(buffer.length);
 *             writeOut.write(buffer);
 *             writeOut.writeLong(myTypes[i].fileLength);
 *             writeOut.writeLong(myTypes[i].lastModified);
 *          }
 *          byte[] buffer = out.toByteArray();
 *          writeOut.close();
 * 
 *          super.javaToNative(buffer, transferData);
 *          
 *       } catch (IOException e) {
 *       }
 *    }
 * }
 * public Object nativeToJava(TransferData transferData){   
 * 
 *    if (isSupportedType(transferData)) {
 *       
 *       byte[] buffer = (byte[])super.nativeToJava(transferData);
 *       if (buffer == null) return null;
 *       
 *       MyType[] myData = new MyType[0];
 *       try {
 *          ByteArrayInputStream in = new ByteArrayInputStream(buffer);
 *          DataInputStream readIn = new DataInputStream(in);
 *          while(readIn.available() > 20) {
 *             MyType datum = new MyType();
 *             int size = readIn.readInt();
 *             byte[] name = new byte[size];
 *             readIn.read(name);
 *             datum.fileName = new String(name);
 *             datum.fileLength = readIn.readLong();
 *             datum.lastModified = readIn.readLong();
 *             MyType[] newMyData = new MyType[myData.length + 1];
 *             System.arraycopy(myData, 0, newMyData, 0, myData.length);
 *             newMyData[myData.length] = datum;
 *             myData = newMyData;
 *          }
 *          readIn.close();
 *       } catch (IOException ex) {
 *          return null;
 *       }
 *       return myData;
 *    }
 * 
 *    return null;
 * }
 * protected String[] getTypeNames(){
 *    return new String[]{MYTYPENAME};
 * }
 * protected int[] getTypeIds(){
 *    return new int[] {MYTYPEID};
 * }
 * }
 * </code></pre>
 *
 * @see Transfer
 * @since 1.3
 */
public abstract class ByteArrayTransfer extends Transfer {

    public TransferData[] getSupportedTypes() {
        int[] types = getTypeIds();
        TransferData[] data = new TransferData[types.length];
        for (int i = 0; i < types.length; i++) {
            data[i] = new TransferData();
            data[i].type = types[i];
        }
        return data;
    }

    public boolean isSupportedType(TransferData transferData) {
        boolean result = false;
        if (transferData != null) {
            int[] types = getTypeIds();
            for (int i = 0; !result && i < types.length; i++) {
                if (transferData.type == types[i])
                    result = true;
            }
        }
        return result;
    }

    /**
     * This implementation of <code>javaToNative</code> converts a java
     * <code>byte[]</code> to a platform specific representation.
     * 
     * @param object a java <code>byte[]</code> containing the data to be
     *          converted
     * @param transferData an empty <code>TransferData</code> object that will be
     *          filled in on return with the platform specific format of the data
     * @see Transfer#nativeToJava
     */
    public void javaToNative(Object object, TransferData transferData) {
        if (!checkByteArray(object) || !isSupportedType(transferData)) {
            DND.error(DND.ERROR_INVALID_DATA);
        }
        byte[] data = (byte[]) object;
        transferData.data = new byte[data.length];
        System.arraycopy(data, 0, transferData.data, 0, data.length);
        transferData.result = 1;
    }

    /**
     * This implementation of <code>nativeToJava</code> converts a platform
     * specific representation of a byte array to a java <code>byte[]</code>.
     * 
     * @param transferData the platform specific representation of the data to be
     *          converted
     * @return a java <code>byte[]</code> containing the converted data if the
     *         conversion was successful; otherwise null
     * @see Transfer#javaToNative
     */
    public Object nativeToJava(TransferData transferData) {
        byte[] result = null;
        if (isSupportedType(transferData) && (transferData.data instanceof byte[])) {
            byte[] data = (byte[]) transferData.data;
            result = new byte[data.length];
            System.arraycopy(data, 0, result, 0, data.length);
        }
        return result;
    }

    private static boolean checkByteArray(Object object) {
        return object != null && object instanceof byte[] && ((byte[]) object).length > 0;
    }
}