尝试访问XSSFShape的父级会导致NullPointerException

Question

在尝试遍历ShapeContainer的内部内容时，我希望通过检查XSSFShapeGroup的父项来区分XSSFPicture和不是XSSFPicture的子项：

private void traverseShapeContainer(ShapeContainer<XSSFShape> container) {
    for (XSSFShape shape : container) {
          // Other types of XSSFShapes have not been mentioned here.
          if (shape instanceof XSSFPicture) {
            XSSFPicture picture = (XSSFPicture) shape;
            System.out.println(shape.getParent() instanceof XSSFShapeGroup); // Always outputs false
            System.out.println(Objects.isNull(shape.getParent())); // Always outputs true
        } else if (shape instanceof XSSFShapeGroup) {
            XSSFShapeGroup shapeGroup = (XSSFShapeGroup) shape;
            // accessing inner contents of XSSFShapeGroup
            traverseShapeContainer(shapeGroup);
        }
    }
}

无论XSSFPicture是否是XSSFShapeGroup的子级，这对于每种情况都是相同的。

• 测试1：检查ShapeContainer是否为XSSFShapeGroup的实例。

System.out.println(Objects.isNull(container instanceof XSSFShapeGroup)); // Output: false

• 测试2：访问子节点后查找父标记。

if (shape instanceof XSSFPicture) {
   XSSFPicture picture = (XSSFPicture) shape;
   // "xdr:grpSp" is the tag for XSSFShapeGroup
   System.out.println(picture.getCTPicture().getDomNode().getParentNode().getNodeName()
                      .equals("xdr:grpSp")); // Output: true
}

这清楚地表明父级确实存在，并且还允许我们在进程中检查父级。

我还没有检查其他类型的XSSFShapes，如XSSFSimpleShape或XSSFConnector。但是，由于它们都继承了同一个类，即xssfshape，我想结果不会有太大不同。

Answer 1

这是因为Apache poi直到现在（2021年5月，版本Apache poi 5.0.0)还不完整。它影响形状组中的所有形状。

XSSFShape.getParent只是返回XSSFShapeGroup Parent的类成员XSSFShapeGroup Parent。但在解析Office Open XML绘图时，apache poi只执行以下操作：

...
 } else if (obj instanceof CTGroupShape) {
  shape = new XSSFShapeGroup(this, (CTGroupShape) obj);
 }...

请参见https://svn.apache.org/viewvc/poi/tags/rel_5_0_0/src/ooxml/java/org/apache/poi/xssf/usermodel/xssfdrawing.java？view=markup#l619。

而XSSFShapeGroup的构造函数只是

protected XSSFShapeGroup(XSSFDrawing drawing, CTGroupShape ctGroup) {
 this.drawing = drawing;
 this.ctGroup = ctGroup;
}

请参见https://svn.apache.org/viewvc/poi/tags/rel_5_0_0/src/ooxml/java/org/apache/poi/xssf/usermodel/xssfshapegroup.java？view=markup#l55。

这样就不需要遍历该组中的所有形状并将其父形状设置为该形状组。因此父始终为空。

例如：

...
 ... void traverseShapeContainer(ShapeContainer<XSSFShape> container) {
  for (XSSFShape shape : container) { 
   // possible:   XSSFConnector, XSSFGraphicFrame, XSSFPicture, XSSFShapeGroup, XSSFSimpleShape
   if (shape instanceof XSSFConnector) {
    XSSFConnector connector = (XSSFConnector)shape;
    System.out.println(connector);

   } else if (shape instanceof XSSFGraphicFrame) {
    XSSFGraphicFrame graphicFrame = (XSSFGraphicFrame)shape;
    System.out.println(graphicFrame);

   } else if (shape instanceof XSSFPicture) {
    XSSFPicture picture = (XSSFPicture)shape;
    System.out.println(picture);
    if (container instanceof XSSFDrawing) {
     System.out.println("Picture is in drawing directly.");
    } else if (container instanceof XSSFShapeGroup) {
     System.out.println("Picture is in shape group.");
     XSSFShapeGroup parent = (XSSFShapeGroup) container;
     System.out.println("Parent is " +  parent);
    }

   } else if (shape instanceof XSSFShapeGroup) { //we have a shape group
    XSSFShapeGroup shapeGroup = (XSSFShapeGroup)shape;
    System.out.println(shapeGroup);

    traverseShapeContainer(shapeGroup); // we now can sinply get the XSSFShapeGroup as ShapeContainer<XSSFShape>

   } else if (shape instanceof XSSFSimpleShape) {
    XSSFSimpleShape simpleShape = (XSSFSimpleShape)shape;
    System.out.println(simpleShape);

   }
  }

 }
...