java - Dom 解析器不工作 - 显示的输出全部为空

Question

我想解析这个名为“Weather.xml”的 xml 文件，如下所示:

<?xml version ="1.0" encoding="UTF-8" ?> 
   <weather> 
       <forecast_information>
                                    <city data="Pittsford, NY" />
                                    <postal_code data="14534" /> 
                                    <forecast_date data="2015-03-12" /> 
                                    <unit_system data="US" />
                                  <condition data = "Mostly Cloudy" /> 
                                   <temp_f data ="42" /> 
                                   <wind_condition data="Wind: NW at 7 mph" /> 
                                    <day_of_week data="Sat" /> 
                                    <low data="32"/> 
                                   <high data = "45" />
                                   <condition data="Rain and Snow" />
          </forecast_information>
         <forecast_information> 
                                    <city data= "Rochester, NY" /> 
                                    <postal_code data="14623" /> 
                                   <forecast_date data= "2015-03-12" /> 
                                   <unit_system data="US" /> 
                                    <condition data="Partly Cloudy" /> 
                                    <temp_f data="40" />
                                    <wind_condition data="Wind: St at 3.5 mph"       />
                                     <day_of_week data="Mon" /> 
                                     <low data="30" /> 
                                     <high data="40" />
                                     <condition data="Bright and Sunny" />
            </forecast_information> 
   </weather> 

我用以下方式为其编写了 DOM 解析器:

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

  try { 
     File inputFile = new File("Weather.xml");
     DocumentBuilderFactory dbFactory 
        = DocumentBuilderFactory.newInstance();
     DocumentBuilder dBuilder = dbFactory.newDocumentBuilder();
     Document doc = dBuilder.parse(inputFile);
     doc.getDocumentElement().normalize();
     System.out.println("Root element :" 
        + doc.getDocumentElement().getNodeName());
     NodeList nList = doc.getElementsByTagName("forecast_information");
     System.out.println("----------------------------");
     for (int temp = 0; temp < nList.getLength(); temp++) {
        Node nNode = nList.item(temp);
        System.out.println("\nCurrent Element :" 
           + nNode.getNodeName());
        if (nNode.getNodeType() == Node.ELEMENT_NODE) {
           Element eElement = (Element) nNode;
           System.out.println("City : " + eElement.getAttribute("city"));

           System.out.println("Postal_Code : " + eElement.getElementsByTagName("postal_code").item(0).getTextContent());
           System.out.println("Forecast date : " + eElement.getElementsByTagName("forecast_date").item(0).getTextContent());
           System.out.println("Unit System : " + eElement .getElementsByTagName("unit_system") .item(0).getTextContent());
           System.out.println("Condition : " + eElement .getElementsByTagName("condition") .item(0).getTextContent());
           System.out.println("Wind Condition : " + eElement .getElementsByTagName("wind_condition") .item(0).getTextContent());
           System.out.println("Day of week : " + eElement .getElementsByTagName("day_of_week") .item(0).getTextContent());
           System.out.println("Low : " + eElement .getElementsByTagName("low") .item(0).getTextContent());
           System.out.println("High: " + eElement .getElementsByTagName("high") .item(0).getTextContent());




        }
     }
  } catch (Exception e) {
     e.printStackTrace();
  }
 }
 }

但是显示的输出如下，信息不是从我提供的 .xml 文件中提取的:

   Root element :weather
   ----------------------------

   Current Element :forecast_information
   City : 
   Postal_Code : 
   Forecast date : 
   Unit System : 
   Condition : 
   Wind Condition : 
   Day of week : 
   Low : 
   High: 

   Current Element :forecast_information
   City : 
   Postal_Code : 
   Forecast date : 
   Unit System : 
   Condition : 
   Wind Condition : 
   Day of week : 
   Low : 
   High: 

Answer 1

第一个错误:

System.out.println("City : " + eElement.getAttribute("city"));

您要求提供名为 city 的元素的属性，但 forecast_information 元素没有任何属性。 city 是 forecast_information 的子元素，因此您应该通过遍历子元素或使用 getElementsByTagName() 来提取它> 正如您对其余项目所做的那样。

第二个错误:

对于所有其他元素，您正在执行getElementsByTagName，这对于检索元素本身来说效果很好。但是，您要检索的data项不是它们的内容 - 它是一个属性。

如果项目如下所示，则使用 getTextContent() 是正确的:

<forecast_date>2015-03-12</forecast_date> 
<unit_system>US</unit_system>

但这不是 XML 的格式。在 XML 中，您需要检索属性 data。所以你应该替换这样的调用:

System.out.println("Postal_Code : " + eElement.getElementsByTagName("postal_code").item(0).getTextContent());

致:

System.out.println("Postal_Code : " + eElement.getElementsByTagName("postal_code").item(0).getAttribute("data"));