VTK/Java Wrapping
Configuration
You basically just need to turn VTK_WRAP_JAVA on in CMake and build.
Bartlomiej Wilkowski has created a nice tutorial of configuring Java wrapping with VTK.
Mac (Snow Leopard)
To build a sample application provided in VTK against your VTK build directory (with an installed VTK replace "bin" with "lib"):
$ export DYLD_LIBRARY_PATH=$DYLD_LIBRARY_PATH:your_vtk_build_dir/bin $ javac -cp your_vtk_build_dir/bin/vtk.jar your_vtk_source_dir/Wrapping/Java/vtk/sample/Demo.java $ java -cp your_vtk_build_dir/bin/vtk.jar:your_vtk_source_dir/Wrapping/Java vtk.sample.Demo
Usage
<source lang="java"> /**
* An application that displays a 3D cone. The button allow to close the * application */
public class SimpleVTK extends JPanel implements ActionListener {
private static final long serialVersionUID = 1L; private vtkPanel renWin; private JButton exitButton;
// -----------------------------------------------------------------
// Load VTK library and print which library was not properly loaded
static {
if (!vtkNativeLibrary.LoadAllNativeLibraries()) {
for (vtkNativeLibrary lib : vtkNativeLibrary.values()) {
if (!lib.IsLoaded()) {
System.out.println(lib.GetLibraryName() + " not loaded");
}
}
}
vtkNativeLibrary.DisableOutputWindow(null);
}
// -----------------------------------------------------------------
public SimpleVTK() {
super(new BorderLayout());
// build VTK Pipeline
vtkConeSource cone = new vtkConeSource();
cone.SetResolution(8);
vtkPolyDataMapper coneMapper = new vtkPolyDataMapper();
coneMapper.SetInputConnection(cone.GetOutputPort());
vtkActor coneActor = new vtkActor();
coneActor.SetMapper(coneMapper);
renWin = new vtkPanel();
renWin.GetRenderer().AddActor(coneActor);
// Add Java UI components
exitButton = new JButton("Exit");
exitButton.addActionListener(this);
add(renWin, BorderLayout.CENTER);
add(exitButton, BorderLayout.SOUTH);
}
/** An ActionListener that listens to the button. */
public void actionPerformed(ActionEvent e) {
if (e.getSource().equals(exitButton)) {
System.exit(0);
}
}
public static void main(String s[]) {
SwingUtilities.invokeLater(new Runnable() {
@Override
public void run() {
JFrame frame = new JFrame("SimpleVTK");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().setLayout(new BorderLayout());
frame.getContentPane().add(new SimpleVTK(), BorderLayout.CENTER);
frame.setSize(400, 400);
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
} </source>
Java Wrapper Refactoring (Oct 8, 2007)
There were a few problems with the old Java wrappers. One was that, as you said, objects were being deleted before they were supposed to. We hacked in a fix at one point about a year ago which basically made all VTK objects accessed from Java stay around forever, but this was not acceptable either.
Ref:
The other major concern was that the map from Java objects to VTK objects was in the C++ JNI layer, and while we tried to keep this map synchronized with a mutex, race conditions could still occur because other Java threads could advance while the JNI layer was being called (a thread could access a C++ object just as it is being garbage-collected and deleted). There does not seem to be a way to atomically call a JNI method, or ensure the collector doesn't run while a method is called. This second issue forced us to rethink how the map is done, and the solution was to keep the map in Java instead of C++. But we didn't want this Java map to prohibit objects from being garbage collected. Fortunately, Java has a WeakReference class for just this type of purpose. When accessed, the reference will either be valid or null depending on whether it has been garbage-collected.
http://java.sun.com/j2se/1.4.2/docs/api/java/lang/ref/WeakReference.html
Thus, the wrapper code can lookup objects in this map when returning objects from methods, and if it is not there, or null, it creates a new Java object representing that C++ object.
A final issue was that we wanted a way to guarantee all C++ destructors are called before the program exits. The natural place to decrement the reference count of the C++ object is in finalize(), which works when things are garbage-collected, but Java does not guarantee that finalize will ever be called. So the method vtkGlobalJavaHash.DeleteAll() will plow through the remaining VTK objects and call Delete on them.
