使用NodeList遍历XML中的所有元素 [英] Loop through all elements in XML using NodeList

问题描述

我想遍历每个XML打印中的所有元素。我的问题是我在 staff1 标记之后不断获得空指针异常，即 john 465456433 gmail1 area1 city1

I want to loop through all elements in a piece of XML printing each one. My problem is that I keep getting a null pointer exception after the staff1 tag, i.e. john 465456433 gmail1 area1 city1

我的Java代码用于打印xml文件中的所有元素：

This my Java code to print all elements in an xml file:

File fXmlFile = new File("file.xml");
DocumentBuilderFactory dbFactory = DocumentBuilderFactory.newInstance();
DocumentBuilder dBuilder = dbFactory.newDocumentBuilder();
Document doc = dBuilder.parse(fXmlFile);

doc.getDocumentElement().normalize();

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

NodeList nList = doc.getElementsByTagName("*");

System.out.println("----------------------------");

Node n=null;
Element eElement=null;

for (int i = 0; i < nList.getLength(); i++) {           
  System.out.println(nList.getLength());     
  n= nList.item(i);                            
  System.out.println("\nCurrent Element :" + n.getNodeName());


  if (n.getNodeType() == Node.ELEMENT_NODE) {
    eElement = (Element) n.getChildNodes();
    System.out.println("\nCurrent Element :" + n.getNodeName());
    name = eElement.getElementsByTagName("name").item(i).getTextContent(); //here throws null pointer exception after printing staff1 tag
    phone = eElement.getElementsByTagName("phone").item(i).getTextContent();
    email = eElement.getElementsByTagName("email").item(i).getTextContent();
    area = eElement.getElementsByTagName("area").item(i).getTextContent();
    city = eElement.getElementsByTagName("city").item(i).getTextContent();
  }
  n.getNextSibling();
}

XML文件：

<?xml version="1.0"?>
<company>
  <staff1>
    <name>john</name>
    <phone>465456433</phone>
    <email>gmail1</email>
    <area>area1</area>
    <city>city1</city>
  </staff1>
  <staff2>
    <name>mary</name>
    <phone>4655556433</phone>
    <email>gmail2</email>
    <area>area2</area>
    <city>city2</city>
  </staff2>
  <staff3>
    <name>furvi</name>
    <phone>4655433</phone>
    <email>gmail3</email>
    <area>area3</area>
    <city>city3</city>
  </staff3>
</company>

预期产出：

john
465456433
gmail1
area1
city1
mary
4655556433
gmail2
area2
city2
furvi
4655433
gmail3
area3
city3

推荐答案

    DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
    DocumentBuilder db = dbf.newDocumentBuilder();
    Document dom = db.parse("file.xml");
    Element docEle = dom.getDocumentElement();
    NodeList nl = docEle.getChildNodes();
    if (nl != null) {
        int length = nl.getLength();
        for (int i = 0; i < length; i++) {
            if (nl.item(i).getNodeType() == Node.ELEMENT_NODE) {
                Element el = (Element) nl.item(i);
                if (el.getNodeName().contains("staff")) {
                    String name = el.getElementsByTagName("name").item(0).getTextContent();
                    String phone = el.getElementsByTagName("phone").item(0).getTextContent();
                    String email = el.getElementsByTagName("email").item(0).getTextContent();
                    String area = el.getElementsByTagName("area").item(0).getTextContent();
                    String city = el.getElementsByTagName("city").item(0).getTextContent();
                }
            }
        }
    }

迭代所有子节点和 nl.item（i）.getNodeType（）== Node.ELEMENT_NODE 用于过滤文本节点。如果XML中没有其他内容，剩下的就是人员节点。

Iterate over all children and nl.item(i).getNodeType() == Node.ELEMENT_NODE is used to filter text nodes out. If there is nothing else in XML what remains are staff nodes.

对于东西下的每个节点（名称，电话，电子邮件，区域，城市）

For each node under stuff (name, phone, email, area, city)

 el.getElementsByTagName("name").item(0).getTextContent(); 

el.getElementsByTagName（name）将提取东西下的名称节点，
.item（0）将获得第一个节点
和。 getTextContent（）将获取文本内容。

el.getElementsByTagName("name") will extract the "name" nodes under stuff, .item(0) will get you the first node and .getTextContent() will get the text content inside.

编辑：
由于我们有杰克逊，我会以不同的方式做到这一点。为对象定义一个pojo：

Since we have jackson I would do this in a different way. Define a pojo for the object:

public class Staff {
    private String name;
    private String phone;
    private String email;
    private String area;
    private String city;
...getters setters
}

然后使用jackson：

Then using jackson:

    JsonNode root = new XmlMapper().readTree(xml.getBytes());
    ObjectMapper mapper = new ObjectMapper();
    root.forEach(node -> consume(node, mapper));



private void consume(JsonNode node, ObjectMapper mapper) {
    try {
        Staff staff = mapper.treeToValue(node, Staff.class);
        //TODO your job with staff
    } catch (JsonProcessingException e) {
        e.printStackTrace();
    }
}

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