JTree DataFlavor问题

时间：2015-07-14 15:35:43

标签： java swing drag-and-drop jtree notserializableexception

我正在为JTree实施D＆amp; D。我编写了自定义TransferHandler并创建了一个新的Transferable类。这个课程非常简单：

public class TreePathTransferable implements Transferable{

  private static final DataFlavor[] flavors = new DataFlavor[] {
          new DataFlavor(TreePath[].class,"TreePaths")};

  private TreePath[] data;

  public TreePathTransferable(TreePath[] data) {
    super();
    this.data = data;
  }

  public DataFlavor[] getTransferDataFlavors() {
    return flavors;
  }

  public boolean isDataFlavorSupported(DataFlavor flavor) {
    return flavors[0].equals(flavor);
  }

  public TreePath[] getTransferData(DataFlavor flavor) throws
          UnsupportedFlavorException, IOException{
    return data;
  }
}

如果“暂停”，我会打电话

dtde.getTransferable().getTransferData(dtde.getTransferable().getTransferDataFlavors()[0])

我得到java.io.NotSerializableException。如果我使用TreePathTransferable按以下方式更改Object中的data-Object：

public class TreePathTransferable implements Transferable{

  private static final DataFlavor[] flavors = new DataFlavor[] {
          new DataFlavor(Object.class,"Object")};

  private Object data;

  public TreePathTransferable(Object data) {
    super();
    this.data = data;
  }

  public DataFlavor[] getTransferDataFlavors() {
    return flavors;
  }

  public boolean isDataFlavorSupported(DataFlavor flavor) {
    return flavors[0].equals(flavor);
  }

  public Object getTransferData(DataFlavor flavor) throws
          UnsupportedFlavorException, IOException{
    return data;
  }

}

一切正常。这对我来说毫无意义。为什么不同？

堆栈跟踪

注意：我已使用XXX替换了非序列化类。这是DefaultMutableTreeNode的子类的属性。这个子类是不可序列化的，所以Exception是有意义的，但为什么她没有出现在第二种情况下呢？

java.io.NotSerializableException: XXX
    at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1184)
    at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1548)
    at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1509)
    at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1432)
    at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1178)
    at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:348)
    at java.util.HashMap.internalWriteEntries(HashMap.java:1777)
    at java.util.HashMap.writeObject(HashMap.java:1354)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:988)
    at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1496)
    at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1432)
    at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1178)
    at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1548)
    at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1509)
    at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1432)
    at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1178)
    at java.io.ObjectOutputStream.writeArray(ObjectOutputStream.java:1378)
    at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1174)
    at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:348)
    at javax.swing.tree.DefaultMutableTreeNode.writeObject(DefaultMutableTreeNode.java:1287)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:988)
    at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1496)
    at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1432)
    at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1178)
    at java.io.ObjectOutputStream.writeArray(ObjectOutputStream.java:1378)
    at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1174)
    at java.io.ObjectOutputStream.access$300(ObjectOutputStream.java:162)
    at java.io.ObjectOutputStream$PutFieldImpl.writeFields(ObjectOutputStream.java:1707)
    at java.io.ObjectOutputStream.writeFields(ObjectOutputStream.java:482)
    at java.util.Vector.writeObject(Vector.java:1077)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:988)
    at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1496)
    at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1432)
    at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1178)
    at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1548)
    at java.io.ObjectOutputStream.defaultWriteObject(ObjectOutputStream.java:441)
    at javax.swing.tree.DefaultMutableTreeNode.writeObject(DefaultMutableTreeNode.java:1278)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:988)
    at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1496)
    at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1432)
    at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1178)
    at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1548)
    at java.io.ObjectOutputStream.defaultWriteObject(ObjectOutputStream.java:441)
    at javax.swing.tree.DefaultMutableTreeNode.writeObject(DefaultMutableTreeNode.java:1278)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:988)
    at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1496)
    at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1432)
    at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1178)
    at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1548)
    at java.io.ObjectOutputStream.defaultWriteObject(ObjectOutputStream.java:441)
    at javax.swing.tree.DefaultMutableTreeNode.writeObject(DefaultMutableTreeNode.java:1278)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:988)
    at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1496)
    at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1432)
    at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1178)
    at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1548)
    at java.io.ObjectOutputStream.defaultWriteObject(ObjectOutputStream.java:441)
    at javax.swing.tree.DefaultMutableTreeNode.writeObject(DefaultMutableTreeNode.java:1278)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at java.io.ObjectStreamClass.invokeWriteObject(ObjectStreamClass.java:988)
    at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1496)
    at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1432)
    at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1178)
    at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1548)
    at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1509)
    at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1432)
    at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1178)
    at java.io.ObjectOutputStream.writeArray(ObjectOutputStream.java:1378)
    at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1174)
    at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:348)
    at sun.awt.datatransfer.TransferableProxy.getTransferData(TransferableProxy.java:83)
    at java.awt.dnd.DropTargetContext$TransferableProxy.getTransferData(DropTargetContext.java:376)

的TransferHandler 

public class MyTreeTransferHandler extends TransferHandler {


  public MyTreeTransferHandler() {
    super();
  }

  protected Transferable createTransferable(JComponent c) {
    Transferable t = null;
    if(c instanceof JTree) {
      JTree tree = (JTree) c;
        t = new TreePathTransferable(tree.getSelectionPaths());
        return t;
    }
    return t;
  }

  public int getSourceActions(JComponent c) {
    return TransferHandler.MOVE;
  }

  public boolean canImport(JComponent c, DataFlavor[] flavors){
    return true;
  }
}

1 个答案:

答案 0 :(得分：1)

您的情况是由三件事引起的：

  1. 您使用了DataFlavor构造函数，在该构造函数中您没有直接指定不序列化传输的数据。无论如何，它都是间接的（请参见DataFlavor.javaJVMLocalObjectMimeType或此question）
  2. D＆D机制尝试对传输的数据进行序列化。原因是：“这使共享DnD和剪贴板数据的应用程序相互隔离。”
  3. D＆D机制通过检查您在DataFlavor构造函数中提供的类而不是传输的对象的运行时类来检查它是否可以序列化数据。

在您的堆栈跟踪之后，可以在TransferableProxy source code中看到：

public Object getTransferData(DataFlavor df)
        throws UnsupportedFlavorException, IOException
    {
        Object data = transferable.getTransferData(df);
        // If the data is a Serializable object, then create a new instance
        // before returning it. This insulates applications sharing DnD and
        // Clipboard data from each other.
        if (data != null && isLocal && df.isFlavorSerializedObjectType()) {
            ByteArrayOutputStream baos = new ByteArrayOutputStream();
            ClassLoaderObjectOutputStream oos =
                new ClassLoaderObjectOutputStream(baos);
            oos.writeObject(data);
            ByteArrayInputStream bais =
                new ByteArrayInputStream(baos.toByteArray());
            try {
                ClassLoaderObjectInputStream ois =
                    new ClassLoaderObjectInputStream(bais,
                                                     oos.getClassLoaderMap());
                data = ois.readObject();
            } catch (ClassNotFoundException cnfe) {

                throw (IOException)new IOException().initCause(cnfe);
            }
        }
        return data;
}

重要的部分是df.isFlavorSerializedObjectType()。 This calls isRepresentationClassSerializable方法实现为return java.io.Serializable.class.isAssignableFrom(representationClass);。

因此，这会将您在DataFlavor构造函数中提供的Class与Serializable接口进行比较。由于TreePath[].class implements Serializable和Object不会，因此不会对Object类执行序列化（使用new DataFlavor(Object.class,"Object")构造函数调用）。

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