Run the following sample:
------------------------------
import java.awt.Toolkit;
import java.awt.datatransfer.Clipboard;
import java.awt.datatransfer.DataFlavor;
import java.awt.datatransfer.SystemFlavorMap;
import java.io.IOException;
import java.io.Reader;
import javax.swing.JLabel;
import javax.swing.TransferHandler;

public class ConstructFlavoredObjectTest {

    private static final String TEST_MIME_TYPE = "text/plain;class="
            + MyStringReader.class.getName();

    public static void main(String[] args) throws Exception {

        final DataFlavor dataFlavor = new DataFlavor(TEST_MIME_TYPE);
        SystemFlavorMap systemFlavorMap = (SystemFlavorMap) SystemFlavorMap.
                getDefaultFlavorMap();
        systemFlavorMap.addUnencodedNativeForFlavor(dataFlavor, "TEXT");
        systemFlavorMap.addFlavorForUnencodedNative("TEXT", dataFlavor);

        TransferHandler transferHandler = new TransferHandler("Test Handler");

        Clipboard clipboard = Toolkit.getDefaultToolkit().getSystemClipboard();
        transferHandler.exportToClipboard(new JLabel("Test"), clipboard,
                TransferHandler.COPY);

        Object clipboardData = clipboard.getData(dataFlavor);
        System.out.println("clipboardData: " + clipboardData);
        if (!(clipboardData instanceof MyStringReader)) {
            throw new RuntimeException("Wrong clipboard data!");
        }
    }

    public static class MyStringReader extends Reader {

        public MyStringReader(Reader reader) {
        }

        @Override
        public int read(char[] cbuf, int off, int len) throws IOException {
            throw new UnsupportedOperationException("Not supported yet.");
        }

        @Override
        public void close() throws IOException {
            throw new UnsupportedOperationException("Not supported yet.");
        }
    }
}
------------------------------ 

The following exception is thrown from time to time:

Exception in thread "main" java.awt.datatransfer.UnsupportedFlavorException: text/plain
        at sun.awt.datatransfer.SunClipboard.getData(SunClipboard.java:215)
        at datatransfer.ConstructFlavoredObjectTestPrev.main(ConstructFlavoredObjectTestPrev.java:30)
Java Result: 1