将xml解析为java

Question

给定以下 xml 示例

<?xml version="1.0" encoding="UTF-8" standalone="no" ?>
<message>
  <id>ce8140c2-14e2-418b-8150-9face6a1aa33</id>
  <company>Plostation</company>
  <content>rovetguekh</content>
</message>

每次我发现长度为零时，这是我在 java 中的代码我不知道为什么虽然消息包含我想要的所有内容，但尝试了

NodeList messageListNodes = docEle.getChildNodes();

它工作正常返回 3 但发现 java.lang.NullPointerException.getTextContent();

convertName = el.getElementsByTagName("id").item(0).getTextContent();

代码

 try {

                    DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
                    DocumentBuilder db = dbf.newDocumentBuilder();
                    Document dom = db.parse(new StringBufferInputStream(currentLine));
                    Element docEle = dom.getDocumentElement();
                    dom.getDocumentElement().normalize();

                    logger.info("Root element :" + dom.getDocumentElement().getNodeName());

                    /* Iterate over companies */
                    NodeList messageListNodes = docEle.getElementsByTagName("message");
                    if (messageListNodes != null) { 
                        int length = messageListNodes.getLength();                      
                        for (int i = 0; i < length; i++) {

                            Node nNode = messageListNodes.item(i);

                            if ( nNode.getNodeType() == Node.ELEMENT_NODE) {

                                Element el = (Element) nNode;

                                convertName = el.getElementsByTagName("id").item(0).getTextContent();
                                name = java.util.UUID.fromString(convertName);

                                message.setId(name);
                                message.setCompany(messageListNodes.item(1).getTextContent());
                                message.setContent(messageListNodes.item(2).getTextContent());
                                logger.debug( name+ company + content);
                                messagelist.add(message);
                            }

                        }
                    }

Answer 1

问题出在 UUID 中，现在可以正常工作了

try {

                    DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
                    DocumentBuilder db = dbf.newDocumentBuilder();
                    Document dom = db.parse(new StringBufferInputStream(currentLine));
                    Element docEle = dom.getDocumentElement();
                    dom.getDocumentElement().normalize();

                    logger.info("Root element :" + dom.getDocumentElement().getNodeName());

                    /* Iterate over companies */
                    NodeList messageListNodes = docEle.getChildNodes();
                    if (messageListNodes != null) { 
                        int length = messageListNodes.getLength();                      
                        for (int i = 0; i < length; i++) {

                            if(messageListNodes.item(i) instanceof Element){
                                message.setId(UUID.fromString(messageListNodes.item(i).getTextContent()));
                                message.setCompany(messageListNodes.item(1).getTextContent());
                                message.setContent(messageListNodes.item(2).getTextContent());

                            }

                            logger.debug( name+ company + content);
                            messagelist.add(message);
                        }

                    }

Answer 2

由于您在根上调用getElementByTagName，而根是“消息”标签本身。这就是为什么MessageListNodes 长度为零的原因。

您可以使用docEle.getElementsByTagName("*"); 来获取此元素（根）下的所有元素，或者您可以通过提供标签名称“id”等来做到这一点。

删除示例工作代码供您参考。

Message.java：

class Message {
      final static String ID = "id", COMPANY = "company", CONTENT = "content";
      java.util.UUID id;
      String company;
      String content;

  public void setId(java.util.UUID id) {
     this.id = id;
  }

  public void setCompany(String company) {
    this.company = company;
  }

  public void setContent(String content) {
    this.content = content;
  }

  public void set(String propertyName, String value) {
    // System.out.println("Tag Name:"+propertyName+" ,value"+value);
    switch (propertyName) {
    case ID: {
        java.util.UUID name = java.util.UUID.fromString(value);
        setId(name);
        break;
    }
    case COMPANY: {
        setCompany(value);
        break;
    }
    case CONTENT: {
        setContent(value);
        break;
    }     
  }

  public String toString() {
    return "Message[ " + id.toString() + "," + company + "," + content + " ]";
  }
}

XmlTesting.java：

public class XmlTestimg {
   public static void main(String[] args) {
    try {

        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
        DocumentBuilder db = dbf.newDocumentBuilder();
        Document dom = db.parse(new FileInputStream(new File("/Users/dkandalam/test.xml")));
        Element docEle = dom.getDocumentElement();
        dom.getDocumentElement().normalize();

        System.out.println("Root element :" + dom.getDocumentElement().getNodeName());

        /* Iterate over companies */
        NodeList messageListNodes = docEle.getElementsByTagName("*");
        System.out.println(messageListNodes.getLength());
        if (messageListNodes != null) {
            int length = messageListNodes.getLength();
            Message message = new Message();
            for (int i = 0; i < length; i++) {

                Node nNode = messageListNodes.item(i);

                if (nNode.getNodeType() == Node.ELEMENT_NODE) {
                    Element el = (Element) nNode;
                    message.set(el.getTagName(), el.getTextContent());
                    // messagelist.add(message);
                }
            }
            System.out.println(message.toString());
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
  }
}

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