尝试使用Gephi工具包将图形导出到png，空白图像结果

Question

我熟悉工具包，只是尝试将一些简单的图形导出到png。我有点关注我在此处找到的幻灯片共享教程：http://www.slideshare.net/gephi/gephi-toolkit-tutorialtoolkit

查看结果时，我得到的只是一张空白图片。有人知道我哪里出错吗？我使用下面的代码：

    //Init a project - and therefore a workspace
    ProjectController pc = Lookup.getDefault().lookup(ProjectController.class);
    pc.newProject();
    Workspace workspace = pc.getCurrentWorkspace();

    //Get a graph model - it exists because we have a workspace
    GraphModel graphModel = Lookup.getDefault().lookup(GraphController.class).getGraphModel();

    //Create three nodes
    Node n0 = graphModel.factory().newNode("n0");
    n0.setLabel("Node 0");
    Node n1 = graphModel.factory().newNode("n1");
    n1.setLabel("Node 1");
    Node n2 = graphModel.factory().newNode("n2");
    n2.setLabel("Node 2");

    //Create three edges
    Edge e1 = graphModel.factory().newEdge(n1, n2, 1, true);
    Edge e2 = graphModel.factory().newEdge(n0, n2, 2, true);
    Edge e3 = graphModel.factory().newEdge(n2, n0, 2, true);   //This is e2's mutual edge

    //Append as a Directed Graph
    DirectedGraph directedGraph = graphModel.getDirectedGraph();
    directedGraph.addNode(n0);
    directedGraph.addNode(n1);
    directedGraph.addNode(n2);
    directedGraph.addEdge(e1);
    directedGraph.addEdge(e2);
    directedGraph.addEdge(e3);

    //Count nodes and edges
    System.out.println("Nodes: " + directedGraph.getNodeCount() + " Edges: " + directedGraph.getEdgeCount());

    //Get a UndirectedGraph now and count edges
    UndirectedGraph undirectedGraph = graphModel.getUndirectedGraph();

    //Layout for 1 minute
    AutoLayout autoLayout = new AutoLayout(10, TimeUnit.SECONDS);
    autoLayout.setGraphModel(graphModel);
    YifanHuLayout firstLayout = new YifanHuLayout(null, new StepDisplacement(1f));
    ForceAtlasLayout secondLayout = new ForceAtlasLayout(null);

    AutoLayout.DynamicProperty adjustBySizeProperty = AutoLayout.createDynamicProperty("forceAtlas.adjustSizes.name", Boolean.TRUE, 0.1f);//True after 10% of layout time
    AutoLayout.DynamicProperty repulsionProperty = AutoLayout.createDynamicProperty("forceAtlas.repulsionStrength.name", new Double(500.), 0f);//500 for the complete period
    autoLayout.addLayout(firstLayout, 0.5f);
    autoLayout.addLayout(secondLayout, 0.5f, new AutoLayout.DynamicProperty[]{adjustBySizeProperty,
        repulsionProperty});
    autoLayout.execute();

    //Preview
    PreviewModel model = Lookup.getDefault().lookup(PreviewController.class).getModel();
    model.getProperties().putValue(PreviewProperty.SHOW_NODE_LABELS, Boolean.TRUE);
    model.getProperties().putValue(PreviewProperty.EDGE_COLOR, new EdgeColor(Color.GRAY));
    model.getProperties().putValue(PreviewProperty.EDGE_THICKNESS, new Float(0.1f));
    model.getProperties().putValue(PreviewProperty.NODE_LABEL_FONT, model.getProperties().
    getFontValue(PreviewProperty.NODE_LABEL_FONT).deriveFont(8));

    //Export full graph, save it to test.png and show it in an image frame
    ExportController ec = Lookup.getDefault().lookup(ExportController.class);
    ec.exportFile(new File("test.png"));
    PNGExporter exporter = (PNGExporter) ec.getExporter("png");
    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    ec.exportStream(baos, exporter);
    byte[] png = baos.toByteArray();
    Image image = ImageIO.read(new ByteArrayInputStream(png));
    ImageFrame frame = new ImageFrame(image);
    frame.setVisible(true);