小贝子编程

JTree D&D DataFlavor issue (在某些情况下为 NotSerializableException)



我正在为JTree实现D&D。我写了一个自定义TransferHandler，并创建了一个新的Transferable类。这个类很简单:

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"on drop"我呼叫

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

我得到一个java.io.NotSerializableException。如果我以以下方式将TreePathTransferable中的数据对象的类更改为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。这对我来说没有意义，因为传输的数据是相同的- TreePath[]。为什么会有不同呢?

堆栈跟踪

注意:我已经用XXX代替了不可序列化的类。这是DefaultMutableTreeNode的一个子类的属性。这个子类是不可序列化的，所以Exception是有意义的，但是为什么它没有出现在第二种情况中?

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)

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;
  }
}

你的情况是由三件事造成的:

    你在没有直接指定不序列化传输数据的地方使用了DataFlavor构造函数。这是一种间接的方式(参见dataflaor)。javaJVMLocalObjectMimeType或此问题)如果可以，D&D机制会尝试序列化传输的数据。原因是:"这隔离了共享免打扰和剪贴板数据的应用程序"。
  1. D&D机制通过检查您在dataflaor构造函数中提供的类来检查是否可以序列化数据，而不是传输对象的运行时类。

在你的堆栈跟踪之后，可以在TransferableProxy源代码中看到:

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;
}

重要部分是df.isFlavorSerializedObjectType()。这调用isRepresentationClassSerializable方法实现为return java.io.Serializable.class.isAssignableFrom(representationClass);。

所以这比较了你在DataFlavor构造函数中提供的类和Serializable接口。由于TreePath[].class实现了Serializable而Object没有，因此Object类不执行序列化(使用new DataFlavor(Object.class,"Object")构造函数调用)。

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