我正在构建简单的家谱应用程序并使用 Jung 来绘制图表。到目前为止，我可以使用 zentus 的 sqlitejdbc 绘制图表并将其保存到嵌入式数据库中。不过，我还没有创建清除 Canvas 的函数，所以我必须重新启动应用程序来测试打开数据库。但是当我想重新加载它们时，应用程序就卡住了，我遇到了这个错误。
path:C:\Users\PaLi\Desktop\psm things\chart4.db Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException at FamTree.vertexPainter.transform(vertexPainter.java:20) at FamTree.vertexPainter.transform(vertexPainter.java:1) at edu.uci.ics.jung.visualization.renderers.BasicVertexRenderer.paintShapeForVertex(BasicVertexRenderer.java:98) at edu.uci.ics.jung.visualization.renderers.BasicVertexRenderer.paintIconForVertex(BasicVertexRenderer.java:74) at edu.uci.ics.jung.visualization.renderers.BasicVertexRenderer.paintVertex(BasicVertexRenderer.java:37) at edu.uci.ics.jung.visualization.renderers.BasicRenderer.renderVertex(BasicRenderer.java:70) at edu.uci.ics.jung.visualization.renderers.BasicRenderer.render(BasicRenderer.java:55) at edu.uci.ics.jung.visualization.BasicVisualizationServer.renderGraph(BasicVisualizationServer.java:367) at edu.uci.ics.jung.visualization.BasicVisualizationServer.paintComponent(BasicVisualizationServer.java:321) at javax.swing.JComponent.paint(JComponent.java:1054) at javax.swing.JComponent.paintToOffscreen(JComponent.java:5221) at javax.swing.RepaintManager$PaintManager.paintDoubleBuffered(RepaintManager.java:1482) at javax.swing.RepaintManager$PaintManager.paint(RepaintManager.java:1413) at javax.swing.RepaintManager.paint(RepaintManager.java:1206) at javax.swing.JComponent._paintImmediately(JComponent.java:5169) at javax.swing.JComponent.paintImmediately(JComponent.java:4980) at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:770) at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:728) at javax.swing.RepaintManager.prePaintDirtyRegions(RepaintManager.java:677) at javax.swing.RepaintManager.access$700(RepaintManager.java:59) at javax.swing.RepaintManager$ProcessingRunnable.run(RepaintManager.java:1621) at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251) at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:705) at java.awt.EventQueue.access$000(EventQueue.java:101) at java.awt.EventQueue$3.run(EventQueue.java:666) at java.awt.EventQueue$3.run(EventQueue.java:664) at java.security.AccessController.doPrivileged(Native Method) at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76) at java.awt.EventQueue.dispatchEvent(EventQueue.java:675) at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:211) at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:128) at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:117) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:113) at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:105) at java.awt.EventDispatchThread.run(EventDispatchThread.java:90)
这是顶点绘制器转换器的代码。如果不加载数据库部分，它工作得很好。
package FamTree;
import org.apache.commons.collections15.Transformer;
import java.awt.*;
import java.util.Map;
class vertexPainter implements Transformer<Integer, Paint>
{
private Map<Integer,Person> tempV;
public vertexPainter(Map<Integer,Person> passV)
{
tempV = passV;
}
public Paint transform(Integer v)
{
if (tempV.get(v).getpSex().equalsIgnoreCase("male"))
return (Color.blue);
else
return (Color.red);
}
}
这是图的初始化并设置 vv。
public TCanvas(){
graph = new SparseMultigraph<Integer,Number>();
layout2 = new StaticLayout<Integer,Number>(graph,new Dimension(2000,2000));
vv = new VisualizationViewer<Integer,Number>(layout2);
vv.setBackground(Color.white);
vv.setVertexToolTipTransformer(new ToStringLabeller<Integer>());
vv.getRenderContext().setVertexFillPaintTransformer(new vertexPainter(vertex));
vv.getRenderer().getVertexLabelRenderer().setPosition(Renderer.VertexLabel.Position.S);
vv.getRenderContext().setVertexLabelTransformer(new vertexLabel(vertex));
vv.getRenderContext().setEdgeDrawPaintTransformer(new edgePainter());
Transformer<Number,String> stringer = new Transformer<Number,String>(){
public String transform(Number e) {
return "Edge:"+e+ "-"+graph.getEndpoints(e).toString();
}
};
vv.getRenderContext().setEdgeLabelTransformer(stringer);
EdgeLabelRenderer edgeLabelRenderer= vv.getRenderContext().getEdgeLabelRenderer();
edgeLabelRenderer.setRotateEdgeLabels(false);
gm = new DefaultModalGraphMouse<Integer, Number>();
vv.setGraphMouse(gm);
gm.add(new PopupGraphMousePlugin());
GraphZoomScrollPane scrollPane2 = new GraphZoomScrollPane(vv);
JPanel vvPanel = new JPanel();
vvPanel.setLayout(new BorderLayout());
vvPanel.add(scrollPane2);
addBottomControls(vvPanel);
Container content = getContentPane();
content.add(vvPanel);
}//TCanvas()
这是加载数据库的部分。
menu.add(new AbstractAction("Open") {
public void actionPerformed(ActionEvent e) {
JFileChooser open = new JFileChooser();
final File file ;
int vat = open.showOpenDialog(rootPane);
if(vat==JFileChooser.APPROVE_OPTION){
file = open.getSelectedFile();
String fPath = file.getAbsolutePath();
System.out.println("path:"+fPath);
try{
Class.forName("org.sqlite.JDBC");
Connection conn = DriverManager.getConnection("jdbc:sqlite:"+fPath);
Statement stat = conn.createStatement();
ResultSet rs = stat.executeQuery("select * from Person;");
while (rs.next()) {
Integer pid = rs.getInt("pID");
String pname = rs.getString("pName");
String psex = rs.getString("pSex");
Integer fatherid = (Integer)rs.getInt("fatherID");
Integer motherid = (Integer)rs.getInt("motherID");
Integer spouseid = (Integer)rs.getInt("spouseID");
Person personInfo = new Person();
personInfo.setpID(pid);
personInfo.setpName(pname);
personInfo.setpSex(psex);
personInfo.setFatherID(fatherid);
personInfo.setMotherID(motherid);
personInfo.setSpouseID(spouseid);
vertex.put(pid,personInfo);
graph.addVertex(pid);
vv.repaint();
ResultSet rs2 = stat.executeQuery("select * from Location;");
while (rs2.next()) {
if(rs2.getInt("pID")==pid){
Point2D.Double loc = new Point2D.Double();
Double x = rs2.getDouble("pointX");
Double y = rs2.getDouble("pointY");
loc.setLocation(x, y);
layout2.setLocation(pid, vv.getRenderContext().getMultiLayerTransformer().inverseTransform(loc));
vv.repaint();
}
}
rs2.close();
}
rs.close();
ResultSet rs3 = stat.executeQuery("select * from Relation;");
while (rs3.next()) {
Point2D.Double loc2 = new Point2D.Double();
Number edgeid = (Number)rs3.getInt("edgeID");
Integer v1 = rs3.getInt("vertex1");
Integer v2 = rs3.getInt("vertex2");
String type = rs3.getString("RelationType");
Relation relation = new Relation(edgeid, v1, v2, type);
edge.put(edgeid, relation);
if(type.equalsIgnoreCase("DIRECTED")){
graph.addEdge(edgeid, v1, v2, EdgeType.DIRECTED);
}
if(type.equalsIgnoreCase("UNDIRECTED")){
graph.addEdge(edgeid, v1, v2, EdgeType.UNDIRECTED);
}
vv.repaint();
}
rs3.close();
conn.close();
vv.repaint();
}
catch (Exception ex) {
// TODO: handle exception
ex.printStackTrace();
}
}
}});
我真的不知道这里发生了什么，因为我很确定打开和检索数据库部分没有问题。
最佳答案
在 vertexPainter#transform 中，贴图要么为 null，要么没有整数键值(“v”)或一条记录的值 pSex 属性为 null(可能未在数据库表上设置)。
调试器可以准确地告诉您实际问题是什么。
<小时/>在 TCanvas 构造函数中，我看到这行代码:
vv.getRenderContext().setVertexFillPaintTransformer(new vertexPainter(vertex));
这是您使用 map 创建画家的地方，但我没有看到该 map 的声明和初始化。因此，很有可能您将空 map 传递给画家，因此画家无法找到键的值(因为 map 是空的)。这肯定会导致 NPE。
<小时/>这不是研究错误日志。在 eclipse 中:
- 切换到调试视角
- 找到“断点” View (通常是右上角的选项卡)
- 在该 View 上有一个带有“J”和感叹号的按钮，工具提示显示“添加 Java 异常断点”
- 单击该按钮并输入 NPE，然后选择 NullPointerException
- 现在您有了一个断点，该断点将在每个空指针异常时停止
- 调试您的应用程序(例如“运行”)
- 最终应用程序将停止，您将在“调试” View 中看到堆栈跟踪。在你的 vertexPainter 的一帧中，选择该行，它将带你到引发 NPE 的代码行。现在您必须查看变量值并使用检查函数。
关于java - 从数据库加载顶点和边时，顶点绘制器遇到错误，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/11922748/