使用工具包将流图传送给Gephi：NullPointerException [英] Streaming Graph to Gephi using toolkit : NullPointerException

问题描述

我试图创建一个正常的图形，并使用Gephi工具包将其传输到Gephi GUI。我正在关注该工具包和流式插件教程。
我的代码无法工作，因为查找API没有返回有效的值。在调试时，我可以发现下面的两种查找方法都返回空值，因为我在使用这些对象访问其他方法时遇到问题。

StreamingServer server = Lookup。 getDefault（）。lookup（StreamingServer.class）;

ServerControllerFactory controllerFactory = Lookup.getDefault（）。lookup（ServerControllerFactory.class）;

由于'server'或'controllerFactory'都为null，所以使用'server'或'controllerFactory'对象访问任何方法都会抛出NullPointerException。例如，在：

ServerController serverController = controllerFactory.createServerController（graph）;
server.register（serverController，context）;

这是我的代码：

  //初始化一个工程 - 因此工作区
 ProjectController pc = Lookup.getDefault（）。lookup（ProjectController.class）; 
 pc.newProject（）; 
工作区工作区= pc.getCurrentWorkspace（）; 
 
 //获取图形实例
 GraphController graphController = Lookup.getDefault（）。lookup（GraphController.class）; 
 GraphModel graphModel = graphController.getModel（）; 
 Graph graph = graphModel.getGraph（）; 
 
 //添加样本图结构数据
节点n1; 
节点n2; 
 n1 = graphModel.factory（）。newNode（）; 
 n2 = graphModel.factory（）。newNode（）; 
 Edge edge = graphModel.factory（）。newEdge（n1，n2）; 
 
 graph.addNode（n1）; 
 graph.addNode（n2）; 
 graph.addEdge（edge）; 
 
 n1.getNodeData（）。setLabel（Node 1）; 
 n2.getNodeData（）。setLabel（Node 2）; 
 edge.getEdgeData（）。setLabel（Edge 1）; 
 
 System.out.println（graph.getNodeCount（）+nodes）; 
 System.out.println（graph.getEdgeCount（）+edges）; 
 System.out.println（）; 
 
 
 StreamingServer server = Lookup.getDefault（）。lookup（StreamingServer.class）; 
 
 ServerControllerFactory controllerFactory = Lookup.getDefault（）。lookup（ServerControllerFactory.class）; 
 ServerController serverController = controllerFactory.createServerController（graph）; 
 
 String context =/ mycontext; 
 server.register（serverController，context）; 
  

解决此问题的任何输入都会有所帮助。

解决方案

如果gephi工具包的 META-inf / services 文件夹不可访问，则可能发生这种情况;例如当你合并罐子;等等，当你尝试做服务器端部署时特别常见。

p.s。类文件在那里;所以不会引发Class Not Found异常;但服务无法找到;欲了解更多信息，请参阅 http://docs.oracle.com /javase/7/docs/api/java/util/ServiceLoader.html

I'm trying to create a normal graph and stream it to Gephi GUI using the Gephi toolkit. I am following the the toolkit and the streaming plugin tutorials. I am having difficulty getting my code to work because the lookup API is not returning valid values. On debug, I could find that both the Lookup methods below return null values because of which I am having trouble in accessing other methods using these objects.

StreamingServer server = Lookup.getDefault().lookup(StreamingServer.class);

ServerControllerFactory controllerFactory = Lookup.getDefault().lookup(ServerControllerFactory.class);

As both 'server' or 'controllerFactory' are null, accessing any methods using 'server' or 'controllerFactory' objects would then throw NullPointerException. For example, at :

ServerController serverController = controllerFactory.createServerController(graph); server.register(serverController, context);

This is the code I have:

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

    // Get the graph instance
    GraphController graphController = Lookup.getDefault().lookup(GraphController.class);
    GraphModel graphModel = graphController.getModel();
    Graph graph = graphModel.getGraph();

    //Add sample graph structure data
       Node n1;
       Node n2;
       n1 = graphModel.factory().newNode();
       n2 = graphModel.factory().newNode();
       Edge edge = graphModel.factory().newEdge(n1, n2);

       graph.addNode(n1);
       graph.addNode(n2);
       graph.addEdge(edge);

       n1.getNodeData().setLabel("Node 1");
       n2.getNodeData().setLabel("Node 2");
       edge.getEdgeData().setLabel("Edge 1");

       System.out.println(graph.getNodeCount() + " nodes");
       System.out.println(graph.getEdgeCount() + " edges");
       System.out.println();


    StreamingServer server = Lookup.getDefault().lookup(StreamingServer.class);

    ServerControllerFactory controllerFactory = Lookup.getDefault().lookup(ServerControllerFactory.class);
    ServerController serverController = controllerFactory.createServerController(graph);

    String context = "/mycontext";
    server.register(serverController, context);

Any inputs to solve this would be helpful.

解决方案

This could happen if META-inf/services folder of gephi toolkit is not accessible; e.g. when you merge jars; etc. especially common when you try to do server side deployment.

p.s. The class files are there; so no Class Not Found exception is thrown; but services are not being able to be located; for more info see http://docs.oracle.com/javase/7/docs/api/java/util/ServiceLoader.html

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