我正在寻找一种完全通用的方法来使用Java1.8的org.w3c.dom.attr从xml属性中获取值？
以下是我尝试的：

import org.w3c.dom.Attr;

String getAttributeValue(Attr attr) {
  if (attr.getSpecified()) {
    String value = attr.getValue();
  }
  else {
    throw new RuntimeException("I don't know how to get an attribute value when."
                             + "it is not specified with the attribute because my "
                             + "implementation does not consider default values in "
                             + "the schema.");
  }
}

根据javadoc for org.w3c.dom.attr，我的解决方案是不完整的，因为我没有涉及在xml文档的模式中给定默认值的情况。如何完成算法，覆盖所有可能存在正确解决方案的情况，并在解决方案不可能时引发异常？
我的attr示例来自一系列以 javax.imageio.ImageIO.getImageReaders(ImageInputStream stream) . 它是这样的：

void processImage(final ImageInputStream stream) throws IOException {
  Iterator<ImageReader> readers = ImageIO.getImageReaders(stream);
  while (readers.hasNext()) {
    ImageReader reader = readers.next();
    reader.setInput(imageInputStream, true);
    IIOMetadata metadata = reader.getImageMetadata(0);
    String[] names = metadata.getMetadataFormatNames();
    int length = names.length;
    for (int i = 0; i < length; ++i) {
      Node node = metadata.getAsTree(names[i]);
      short type = node.getNodeType();
      if(type == Node.ATTRIBUTE_NODE) {
        System.out.print(name[i])
        System.out.print(" = ");
        String attributeValue = getAttributeValue(node);
        System.out.println(attributeValue);
      }
    }
  }
}