JAVA中的DOM到XML不起作用

我已经编写了以下代码

        DocumentBuilderFactory docFactory = DocumentBuilderFactory.newInstance();
        DocumentBuilder docBuilder = docFactory.newDocumentBuilder();

        Document doc = docBuilder.newDocument();

        // Unniversity tag
        Element rootElement = doc.createElement("university");

        // Unniversity attrs
        Attr uniName = doc.createAttribute("name");
        uniName.setNodeValue(university.name);
        Attr uniLogo = doc.createAttribute("logo");
        uniLogo.setNodeValue(university.pathToLogo);
        Attr uniMission = doc.createAttribute("mission");
        uniMission.setNodeValue(university.mission);
        Attr uniVision = doc.createAttribute("vision");
        uniVision.setNodeValue(university.vision);

        rootElement.setAttributeNode(uniName);
        rootElement.setAttributeNode(uniLogo);
        rootElement.setAttributeNode(uniMission);
        rootElement.setAttributeNode(uniVision);

在调试时，当我检查

doc

的值时，我发现如下

doc = (com.sun.org.apache.xerces.internal.dom.DocumentImpl) [#document: null]

---

我做错了什么？我遵循了。

我犯了一个愚蠢的错误，即我没有用

doc

绑定/添加

rootElement

更新代码：

    DocumentBuilderFactory docFactory = DocumentBuilderFactory.newInstance();
    DocumentBuilder docBuilder = docFactory.newDocumentBuilder();

    Document doc = docBuilder.newDocument();

    // Unniversity tag
    Element rootElement = doc.createElement("university");
    doc.appendChild(rootElement);                     // I forgot to add this statement
    // Unniversity attrs
    Attr uniName = doc.createAttribute("name");
    uniName.setNodeValue(university.name);
    Attr uniLogo = doc.createAttribute("logo");
    uniLogo.setNodeValue(university.pathToLogo);
    Attr uniMission = doc.createAttribute("mission");
    uniMission.setNodeValue(university.mission);
    Attr uniVision = doc.createAttribute("vision");
    uniVision.setNodeValue(university.vision);

    rootElement.setAttributeNode(uniName);
    rootElement.setAttributeNode(uniLogo);
    rootElement.setAttributeNode(uniMission);
    rootElement.setAttributeNode(uniVision);

---

在代码中，您没有设置文档的内容。您应该添加以下内容：

document.appendChild(rootElement);

要确认文档包含XML结构，可以打印以下语句：\

System.out.println(document.getDocumentElement());

这将打印[大学：空]