Question

我需要获取Device ID，DeviceType，第一个LastKnownValue标记的数据。 XML是

<?xml version="1.0" encoding="utf-8"?>
  <DeviceList Devid="" Count="35">
    <Device ID="01">
      <Name>@@@@@</Name>
      <DeviceType>Me</DeviceType>
      <ValueVariables Count="3">
        <LastKnownValue Index="1" EndPoint="1" Name="STATE" Type="Bool">false</LastKnownValue>
        <LastKnownValue Index="2" EndPoint="1" Name="LOW BATTERY" Type="Bool">0</LastKnownValue>
        <LastKnownValue Index="3" EndPoint="1" Name="TAMPER" Type="Bool">false</LastKnownValue>
      </ValueVariables>
    </Device>
 </DeviceList>

我尝试了以下代码，但无法获取属性的值。

DocumentBuilderFactory dbFactory = DocumentBuilderFactory.newInstance();
DocumentBuilder dBuilder = dbFactory.newDocumentBuilder();
Document doc = dBuilder.parse("xml path");
doc.getDocumentElement().normalize();
NodeList devicelist =   doc.getDocumentElement().getElementsByTagName("Device");
System.out.println(devicelist.getLength());
for (int i = 0; i < devicelist.getLength(); ++i) 
{
        Element rule = (Element) devicelist.item(i);
        //Device ID
        String ruleid = rule.getAttribute("ID");
        System.out.println(ruleid);
}

Answer 1

我建议使用XPath直接从XML获取节点值，而不是遍历并获取所需的节点。

如果Device节点只出现一次，那么您可以使用下面的XPath表达式来获取数据。

得到XPath的

Device ID是 - //*/Device/@ID或/DeviceList/Device/@ID

得到XPath的

DeviceType是 - //*/DeviceType或/DeviceList/Device/DeviceType

XPath获得第一个LastKnownValue - (//*/LastKnownValue)[1]

Answer 2

如评论中所述，您可以使用XPath查询直接从doc中提取信息。

尝试查看this link。

这是一个代码示例：

try {
   // Build structures to parse the String
   DocumentBuilder builder = DocumentBuilderFactory.newInstance().newDocumentBuilder();
   // Create an XPath query
   XPath xPath =  XPathFactory.newInstance().newXPath();
   // Query the DOM object with the query 
   NodeList nodeList = (NodeList) xPath.compile("//hello").evaluate(document, XPathConstants.NODESET);
 } catch (Exception e) {
     e.printStackTrace();
 }

Answer 3

使用JAXB的完整功能示例：

public static void main(String[] args) throws Exception {
    JAXBContext ctx = JAXBContext.newInstance(DeviceList.class);
    Unmarshaller um = ctx.createUnmarshaller();
    DeviceList deviceList = (DeviceList) um.unmarshal(new File("example.xml"));
    for (Device device : deviceList.devices) {
        System.out.println(device.id);
        System.out.println(device.deviceType);
        if (device.valueVariables.lastKnownValues.size() > 0) {
            LastKnownValue lkv = device.valueVariables.lastKnownValues.get(0);
            System.out.println(lkv.value);
        }
    }
}

@XmlRootElement(name="DeviceList")
public class DeviceList {
    @XmlAttribute(name="Devid")
    public String devid;
    @XmlAttribute(name="Count")
    public Integer count;
    @XmlElement(name="Device")
    public List<Device> devices;
}

public class Device {
    @XmlAttribute(name="ID")
    public String id;
    @XmlElement(name="Name")
    public String name;
    @XmlElement(name="DeviceType")
    public String deviceType;
    @XmlElement(name="ValueVariables")
    public ValueVariables valueVariables;
}

public class ValueVariables {
    @XmlAttribute(name="Count")
    public Integer count;
    @XmlElement(name="LastKnownValue")
    public List<LastKnownValue> lastKnownValues;
}

public class LastKnownValue {
    @XmlAttribute(name="Index")
    public Integer index;
    @XmlAttribute(name="EndPoint")
    public Integer endPoint; // maybe a String?
    @XmlAttribute(name="Name")
    public String name;
    @XmlAttribute(name="Type")
    public String type;
    @XmlValue
    public String value;
}

如何获取xml的内部属性值

3 个答案: