创建XML文件时的TransformerExeption

Question

我正在制作一个Java测试程序。我需要一种将问题保存到XML文件中的方法。所以我的QuestionSaver类需要一个Question并将其保存到一个XML文件中。生成文档很顺利，但我得到了一个TransformerException。我生成文档的方式肯定有问题，但我不知道是什么。

这是我代码的一部分：

/**
 * Default constructor for the QuestionSaver
 */
public QuestionSaver(){
}
public void saveQuestion(Question question) throws ParserConfigurationException {
    DocumentBuilderFactory docFactory = DocumentBuilderFactory.newInstance();
    DocumentBuilder docBuilder = docFactory.newDocumentBuilder();
    // create the quiz root element
    Document doc = docBuilder.newDocument();
    Element rootElement = doc.createElement("question");
    doc.appendChild(rootElement);
    save(rootElement, doc, question);
}
/**
 * General method for saving the question to the xml file
 */
private void save(Element rootElement, Document doc, Question question) {
    /* first, save the question type independent properties */
    SaveIndependentProperties(rootElement, doc, question);
    /* Save the generated Document to an XML file */
    try {
        SaveToFile(doc);
    } catch (TransformerConfigurationException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}
/**
 * Saves the created document to an XML file
 * 
 * @throws TransformerConfigurationException
 */
private void SaveToFile(Document doc) throws TransformerConfigurationException {
    try {
        TransformerFactory transformerFactory = TransformerFactory.newInstance();
        Transformer transformer = transformerFactory.newTransformer();
        DOMSource source = new DOMSource(doc);
        // StreamResult result = new StreamResult(new File("C:\file.xml"));
        // Output to console for testing
        StreamResult result = new StreamResult(System.out);
        transformer.transform(source, result);
    } catch (TransformerException e) {
        System.out.println("TransformerException got thrown!");
    }
    System.out.println("File saved!");
}
/**
 * Saves the properties of a question, which are independent from the questiontype
 * 
 * @param rootElement
 */
private void SaveIndependentProperties(Element rootElement, Document doc, Question question) {
    /* add the actual question */
    Element actualquestion = doc.createElement("actualquestion");
    actualquestion.appendChild(doc.createTextNode(question.getQuestion()));
    rootElement.appendChild(actualquestion);
    /* add the score */
    Element score = doc.createElement("score");
    score.appendChild(doc.createTextNode(Integer.toString(question.getScore())));
    rootElement.appendChild(score);
    /* add the type */
    QuestionType questionType = question.getType();
    Element type = doc.createElement("type");
    type.appendChild(doc.createTextNode(getQuestionTypeString(questionType)));
    rootElement.appendChild(type);
    /* add the source */
    Element source = doc.createElement("source");
    source.appendChild(doc.createTextNode(question.getSource()));
    rootElement.appendChild(source);
    /* add the extra information */
    Element extraInformation = doc.createElement("extrainformation");
    extraInformation.appendChild(doc.createTextNode(question.getExtraInformation()));
    rootElement.appendChild(extraInformation);
}
/**
 * Converts a QuestionType to a string representing the QuestionType
 * 
 * @param questionType the QuestionType
 * @return
 */
private String getQuestionTypeString(QuestionType questionType) {
    if (questionType == QuestionType.MULTIPLEANSWER)
        return "multipleanswer";
    else if (questionType == QuestionType.MULTIPLECHOICE)
        return "multiplechoice";
    else
        return "speed";
}
     static void main(String args[]) {
      try {
        new QuestionSaver().saveQuestion(question);
    } catch (Exception e) {
        e.printStackTrace();
    }

}

Answer 1

我对您的代码进行了一些更新并进行了试用。对我来说，它是有效的。需要记住的事项：您在类的构造函数中启动了保存过程。这很可能是你麻烦的原因。在构造函数中执行保存步骤几乎总是违反最佳java实践。在我的类中，整个过程是无状态的，这意味着您可以在代码的不同点使用相同的QuestionSaver实例，而不会出现问题。看看代码是如何在文件末尾的main方法中执行的。

public class QuestionSaver {
    /**
     * Public constructor for the QuestionSaver
     * 
     * @param question the question to be saved
     * @throws ParserConfigurationException
     */
    public QuestionSaver(){
    }
    public void saveQuestion(Question question) throws ParserConfigurationException {
        DocumentBuilderFactory docFactory = DocumentBuilderFactory.newInstance();
        DocumentBuilder docBuilder = docFactory.newDocumentBuilder();
        // create the quiz root element
        Document doc = docBuilder.newDocument();
        Element rootElement = doc.createElement("question");
        doc.appendChild(rootElement);
        save(rootElement, doc, question);
    }
    /**
     * General method for saving the question to the xml file
     */
    private void save(Element rootElement, Document doc, Question question) {
        /* first, save the question type independent properties */
        SaveIndependentProperties(rootElement, doc, question);
        /* Save the generated Document to an XML file */
        try {
            SaveToFile(doc);
        } catch (TransformerConfigurationException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    /**
     * Saves the created document to an XML file
     * 
     * @throws TransformerConfigurationException
     */
    private void SaveToFile(Document doc) throws TransformerConfigurationException {
        try {
            TransformerFactory transformerFactory = TransformerFactory.newInstance();
            Transformer transformer = transformerFactory.newTransformer();
            DOMSource source = new DOMSource(doc);
            // StreamResult result = new StreamResult(new File("C:\file.xml"));
            // Output to console for testing
            StreamResult result = new StreamResult(System.out);
            transformer.transform(source, result);
        } catch (TransformerException e) {
            System.out.println("Fout met transformen!");
        }
        System.out.println("File saved!");
    }
    /**
     * Saves the properties of a question, which are independent from the questiontype
     * 
     * @param rootElement
     */
    private void SaveIndependentProperties(Element rootElement, Document doc, Question question) {
        /* add the actual question */
        Element actualquestion = doc.createElement("actualquestion");
        actualquestion.appendChild(doc.createTextNode(question.getQuestion()));
        rootElement.appendChild(actualquestion);
        /* add the score */
        Element score = doc.createElement("score");
        score.appendChild(doc.createTextNode(Integer.toString(question.getScore())));
        rootElement.appendChild(score);
        /* add the type */
        QuestionType questionType = question.getType();
        Element type = doc.createElement("type");
        type.appendChild(doc.createTextNode(getQuestionTypeString(questionType)));
        rootElement.appendChild(type);
        /* add the source */
        Element source = doc.createElement("source");
        source.appendChild(doc.createTextNode(question.getSource()));
        rootElement.appendChild(source);
        /* add the extra information */
        Element extraInformation = doc.createElement("extrainformation");
        extraInformation.appendChild(doc.createTextNode(question.getExtraInformation()));
        rootElement.appendChild(extraInformation);
    }
    /**
     * Converts a QuestionType to a string representing the QuestionType
     * 
     * @param questionType the QuestionType
     * @return
     */
    private String getQuestionTypeString(QuestionType questionType) {
        if (questionType == QuestionType.MULTIPLEANSWER)
            return "multipleanswer";
        else if (questionType == QuestionType.MULTIPLECHOICE)
            return "multiplechoice";
        else
            return "speed";
    }
    public static void main(String[] args) {
        try {
            new QuestionSaver().saveQuestion(new Question());
        } catch (Exception e) {
            e.printStackTrace();
        }        
    }
}