Jfreechart.draw（）拋出Nullpointerexception

Question

問題：chart.draw((Graphics2D) emffile.create(), new Rectangle(1500, 600))拋出Nullpointerexception。

可以生成條形圖。請幫忙看看這個問題。

這裏我的代碼：

CategoryDataset dataset = createDataset(); 
JFreeChart chart = createChart(dataset); 

emffile = new EMFGraphics2D(
     new File("C:\\Workspace\\eclipse\\MSReoprt\\chart.emf"), 
     new Dimension(1500, 600) 
); 
emffile.setDeviceIndependent(true); 

emffile.setRenderingHint(
    RenderingHints.KEY_RENDERING, 
    RenderingHints.VALUE_RENDER_QUALITY 
); 
emffile.setRenderingHint(
    RenderingHints.KEY_STROKE_CONTROL, 
    RenderingHints.VALUE_STROKE_NORMALIZE 
); 
emffile.startExport(); 
chart.draw((Graphics2D) emffile.create(), new Rectangle(1500, 600)); 
emffile.endExport(); 
emffile.closeStream(); 

類別和jfreechart的方法：

private CategoryDataset createDataset() 
{ 
    String series = "Availability"; 

    String category1 = "Portal"; 
    String category2 = "DB"; 

    DefaultCategoryDataset dataset = new DefaultCategoryDataset(); 
    dataset.addValue(100, series, category1); 
    dataset.addValue(90, series, category2); 
    return dataset; 
} 

public JFreeChart createChart(CategoryDataset dataset) 
{ 
    FreeChart chart = ChartFactory.createBarChart 
    (
     "Bar Chart Demo", //chart title 
     "Category", //domain axis label 
     "", //range axis label 
     dataset, //data 
     PlotOrientation.VERTICAL, //orientation 
     true, //include legend 
     true, //tooltips? 
     false //URLs? 
    ); 

    //set the background color for the chart... 
    chart.setBackgroundPaint(Color.white); 

    //get a reference to the plot for further customisation... 
    CategoryPlot plot = chart.getCategoryPlot(); 
    plot.setBackgroundPaint(Color.white); 
    plot.setDomainGridlinePaint(Color.white); 
    plot.setRangeGridlinePaint(Color.gray); 

    //set the range axis to display integers only... 
    NumberAxis rangeAxis = (NumberAxis) plot.getRangeAxis(); 
    rangeAxis.setStandardTickUnits(NumberAxis.createIntegerTickUnits()); 

    //disable bar outlines... 
    BarRenderer renderer = (BarRenderer) plot.getRenderer(); 
    renderer.setDrawBarOutline(false); 
    renderer.setMaximumBarWidth(0.5); 
    renderer.setItemMargin(4); 

    //set up gradient paints for series... 
    GradientPaint gp0 = new GradientPaint(
     0.0f, 0.0f, Color.blue, 
     0.0f, 0.0f, Color.MAGENTA 
    ); 
    //GradientPaint gp1 = new GradientPaint(0.0f, 0.0f, Color.green, 
    //0.0f, 0.0f, Color.lightGray); 
    //GradientPaint gp2 = new GradientPaint(0.0f, 0.0f, Color.red, 
    //0.0f, 0.0f, Color.lightGray); 
    renderer.setSeriesPaint(0, gp0); 
    //renderer.setSeriesPaint(1, gp1); 
    //renderer.setSeriesPaint(2, gp2); 

    CategoryAxis domainAxis = plot.getDomainAxis(); 
    domainAxis.setCategoryLabelPositions(
     CategoryLabelPositions.createUpRotationLabelPositions(Math.PI/6.0) 
    ); 
    return chart; 
} 

添加堆棧跟蹤：

Exception in thread "main" java.lang.NullPointerException 
at org.freehep.graphicsio.emf.EMFGraphics2D.writePen(EMFGraphics2D.java:679) 
at org.freehep.graphicsio.emf.EMFGraphics2D.writeStroke(EMFGraphics2D.java:575) 
at org.freehep.graphicsio.AbstractVectorGraphicsIO.setStroke(AbstractVectorGraphicsIO.java:981) 
at org.jfree.chart.plot.Plot.drawOutline(Plot.java:1125) 
at org.jfree.chart.renderer.category.AbstractCategoryItemRenderer.drawOutline(AbstractCategoryItemRenderer.java:717) 
at org.jfree.chart.plot.CategoryPlot.draw(CategoryPlot.java:3684) 
at org.jfree.chart.JFreeChart.draw(JFreeChart.java:1229) 
at org.jfree.chart.JFreeChart.draw(JFreeChart.java:1112) 
at chart.BarChartDemo.export(BarChartDemo.java:61) 
at chart.BarChartDemo.test(BarChartDemo.java:39) 
at chart.BarChartDemo.main(BarChartDemo.java:137) 

Answer 1

我在JFreeChart的論壇貼出this answer：

這看起來像我在EMFGraphics2D類中的錯誤。空 指針異常是發生在行679：

678 private void writePen(BasicStroke stroke, Color color) throws IOException { 
679  if (color.equals(penColor) && stroke.equals(getStroke())) 

我沒有運行代碼，但據推測是「顏色」或「撫摸」是 空。由於代碼行575到達這裏，似乎 「色」是空項（因爲「撫摸」不爲空，因爲它通過了測試的 實例）：在所有

573 public void writeStroke(Stroke stroke) throws IOException { 
574  if (stroke instanceof BasicStroke) { 
575   writePen((BasicStroke) stroke, getColor());[/code] 

現在我見過的Graphics2D實現，getColor（） 從來沒有返回null（我已經寫了測試用例來探討這種行爲）。但檢查EMFGraphics2D代碼，看起來好像 這是默認的加任何調用setPaint（）與非顏色 參數將重置顏色爲空。我認爲這是錯誤的。