Question

我一直致力于将数据转换为基于XML的Collada .DAE格式的工具。不幸的是，有一件事阻止了我：我导出的XML没有任何元素！

这是代码。我已经让它易于阅读，所以你不必经历阅读它的麻烦。

public class DAEExport {
    private static boolean alreadyConstructed = false;
    private static Document doc = null;
    private static Element root = null;
    private static Element lib_images_base_element = null;
    private static Element lib_geometry_base_element = null;
    private static Element lib_control_base_element = null;
    private static Element lib_visual_scene_base_element = null;

    public static void AppendData() {
         //Normally this method would have the data to append as its args, but I'm not worried about that right now.
         //Furthermore, ASSUME THIS RUNS ONLY ONCE (It runs once in the test code I'm using to run this method)! I know that it won't work if called multiple times, as the below variables for the document builder and such wouldn't exist the second time around
         try {
             if (!alreadyConstructed) {
                 alreadyConstructed = true;
                 DocumentBuilderFactory docFactory = DocumentBuilderFactory.newInstance();
                 DocumentBuilder docBuilder = docFactory.newDocumentBuilder();
                 Document document = docBuilder.newDocument();

                 Element rootElement = document.createElement("SomeGenericElement");
                 rootElement.appendChild(document.createTextNode("Generic test contents");

                 document.appendChild(rootElement);

                 doc = document;
             }
         } catch (Exception e) {
             e.printStackTrace();
         }
    }

    public static void Build(File _out) {
        try {
            TransformerFactory transformerFactory = TransformerFactory.newInstance();
            Transformer transformer = transformerFactory.newTransformer();
            DOMSource source = new DOMSource(doc);
            StreamResult result = new StreamResult(System.out);


            transformer.transform(source, result);

            alreadyConstructed = false;
            doc = null;
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

好的，这就是我的问题：尽管通过调用AppendData()将这些元素添加到文档中，然后调用Build()来打印数据，我只获得以下数据：

<?xml version="1.0" encoding="UTF-8"?> - 没有元素。只是基本的标题。就是这样。

我不知道是不是因为一些愚蠢的错误，我在过去的一段时间内都没有注意到，或者别的什么。关于为什么我的元素消失的任何答案？

Answer 1

目前，您的doc对象未从AppendData()方法传递到Build()方法。所有Build()使用都是来自声明的空文档：doc = null。因此，您的结果是空的节点（TransformFactory添加XML标头）。

考虑将doc对象从AppendData()返回到其他方法的类级别（请注意将void更改为返回的对象类型）。然后，您重新定义doc并将其传递到Build()：

public static Document AppendData() {
    ...
    doc = document
    return(doc)
}

或者，在Build()内拨打AppendData，将doc作为参数传递：

public static void AppendData() {
    ...
    doc = document
    Build(doc, outfile)
}

public static void Build(Document doc, File _out) { 
    ...
}

我的XML不是导出元素。为什么？

1 个答案: