試圖解析Java和存儲變量的XML文件中的一個ArrayList

Question

我試圖解析以下XML文件中的Java和到XTimeStamp變量存儲在一個ArrayList和YVoltage在另一個的ArrayList：

<?xml version = "1.0"?> 
<Data> 
<reading> 
    <XTimeStamp> 12:00:00:01</XTimeStamp> 
    <YVoltage> 0.6</YVoltage> 
</reading> 



<reading> 
    <XTimeStamp> 12:00:00:02</XTimeStamp> 
    <YVoltage> 0.5</YVoltage> 
</reading> 



<reading> 
    <XTimeStamp> 12:00:00:025</XTimeStamp> 
    <YVoltage> 0.5</YVoltage> 
</reading> 



<reading> 
    <XTimeStamp> 12:00:00:031</XTimeStamp> 
    <YVoltage> 0.1</YVoltage> 
</reading> 



<reading> 
    <XTimeStamp> 12:00:00:039</XTimeStamp> 
    <YVoltage> -0.1</YVoltage> 
</reading> 



<reading> 
    <XTimeStamp> 12:00:00:050</XTimeStamp> 
    <YVoltage> -0.2</YVoltage> 
</reading> 


<reading> 
    <XTimeStamp> 12:00:01:01</XTimeStamp> 
    <YVoltage> 0.01</YVoltage> 
</reading> 
</Data> 

這裏是Java代碼，我現在必須完成的任務：

import java.util.*; 
import java.io.File; 
import javax.xml.parsers.DocumentBuilder; 
import javax.xml.parsers.DocumentBuilderFactory; 
import org.w3c.dom.Document; 
import org.w3c.dom.Element; 
import org.w3c.dom.Node; 
import org.w3c.dom.NodeList; 

public class XMLReader { 

    public static void main(String argv[]) { 
     ArrayList XTimeStamp = new ArrayList(); 
     ArrayList YVoltage = new ArrayList(); 

     try { 
      File file = new File("C:\\Users\\user\\My Documents\\MyXMLFile.xml"); 
      DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance(); 
      DocumentBuilder db = dbf.newDocumentBuilder(); 
      Document doc = db.parse(file); 
      doc.getDocumentElement().normalize(); 
      System.out.println("Root element " 
        + doc.getDocumentElement().getNodeName()); 
      NodeList nodeLst = doc.getElementsByTagName("reading"); 
      System.out.println("Data"); 

      for (int s = 0; s < nodeLst.getLength(); s++) { 

       Node fstNode = nodeLst.item(s); 

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

        Element fstElmnt = (Element) fstNode; 
        NodeList fstNmElmntLst = fstElmnt 
          .getElementsByTagName("XTimeStamp"); 
        Element fstNmElmnt = (Element) fstNmElmntLst.item(0); 
        NodeList fstNm = fstNmElmnt.getChildNodes(); 
        Element TimeStamp = (Element) fstNmElmntLst.item(0); 
        XTimeStamp.add(TimeStamp); 
        System.out.println("XTimeStamp : " 
          + ((Node) fstNm.item(0)).getNodeValue()); 
        NodeList lstNmElmntLst = fstElmnt 
          .getElementsByTagName("YVoltage"); 
        Element lstNmElmnt = (Element) lstNmElmntLst.item(0); 
        NodeList lstNm = lstNmElmnt.getChildNodes(); 
        Element YValue = (Element) lstNm; 
        YVoltage.add(YValue); 
        System.out.println("YVoltage : " 
          + ((Node) lstNm.item(0)).getNodeValue()); 
       } 

      } 
     } catch (Exception e) { 
      e.printStackTrace(); 
     } 
     System.out.println(XTimeStamp); 
     System.out.println(YVoltage); 
    } 
} 

當我跑我得到下面的輸出，這可以從底部的的ArrayList的列表中可以看出是有問題的代碼：

Root element Data 
Data 
XTimeStamp : 12:00:00:01 
YVoltage : 0.6 
XTimeStamp : 12:00:00:02 
YVoltage : 0.5 
XTimeStamp : 12:00:00:025 
YVoltage : 0.5 
XTimeStamp : 12:00:00:031 
YVoltage : 0.1 
XTimeStamp : 12:00:00:039 
YVoltage : -0.1 
XTimeStamp : 12:00:00:050 
YVoltage : -0.2 
XTimeStamp : 12:00:01:01 
YVoltage : 0.01 
[[XTimeStamp: null], [XTimeStamp: null], [XTimeStamp: null], [XTimeStamp: null], [XTimeStamp: null], [XTimeStamp: null], [XTimeStamp: null]] 
[[YVoltage: null], [YVoltage: null], [YVoltage: null], [YVoltage: null], [YVoltage: null], [YVoltage: null], [YVoltage: null]] 

任何幫助，將不勝感激。

謝謝。

Answer 1

試試這個：

相反的：

Element TimeStamp = (Element) fstNmElmntLst.item(0); 
XTimeStamp.add(TimeStamp); 

DO（如果你可以添加字符串到XTimeStamp）：

String timeStamp = fstNm.item(0)).getNodeValue(); 
XTimeStamp.add(timeStamp); 

或者，如果你想保存元素做到這一點（我'd推薦你保存字符串）

Element timeStamp = (Element) fstNm.item(0)); 
XTimeStamp.add(timeStamp); 

請記住，Java中的約定是用第一個字母小寫來命名變量。

Answer 2

我不明白爲什麼你把你的ArrayList XML元素（其中toString方法顯示標記名稱，並從我記得，關於包含屬性，但不是內部文本的一些信息），而當你做你的System.out.println呼籲您花時間將XML元素轉換爲其有效內容。

我的建議是？把你用於你的System.out.println的字符串放到ArrayLists中。

Answer 3

我覺得它更容易使用XPath這種類型的XML數據彙總：

package net.davymeers; 

import java.io.ByteArrayInputStream; 
import java.io.IOException; 
import java.io.UnsupportedEncodingException; 
import java.util.ArrayList; 
import java.util.Collection; 

import javax.xml.parsers.DocumentBuilder; 
import javax.xml.parsers.DocumentBuilderFactory; 
import javax.xml.parsers.ParserConfigurationException; 
import javax.xml.xpath.XPath; 
import javax.xml.xpath.XPathConstants; 
import javax.xml.xpath.XPathExpression; 
import javax.xml.xpath.XPathExpressionException; 
import javax.xml.xpath.XPathFactory; 

import org.w3c.dom.Document; 
import org.w3c.dom.NodeList; 
import org.xml.sax.SAXException; 

public class XpathTest { 
    private static String XMLSTRING = "<data>" + "<reading>\r\n" 
      + " <XTimeStamp> 12:00:00:02</XTimeStamp>\r\n" 
      + " <YVoltage> 0.5</YVoltage>\r\n" + "</reading>\r\n" + "\r\n" 
      + "\r\n" + "\r\n" + "<reading>\r\n" 
      + " <XTimeStamp> 12:00:00:025</XTimeStamp>\r\n" 
      + " <YVoltage> 0.5</YVoltage>\r\n" + "</reading>\r\n" + "\r\n" 
      + "\r\n" + "\r\n" + "<reading>\r\n" 
      + " <XTimeStamp> 12:00:00:031</XTimeStamp>\r\n" 
      + " <YVoltage> 0.1</YVoltage>\r\n" + "</reading>\r\n" + "\r\n" 
      + "\r\n" + "\r\n" + "<reading>\r\n" 
      + " <XTimeStamp> 12:00:00:039</XTimeStamp>\r\n" 
      + " <YVoltage> -0.1</YVoltage>\r\n" + "</reading>\r\n" + "\r\n" 
      + "\r\n" + "\r\n" + "<reading>\r\n" 
      + " <XTimeStamp> 12:00:00:050</XTimeStamp>\r\n" 
      + " <YVoltage> -0.2</YVoltage>\r\n" + "</reading>\r\n" 
      + "</data>"; 

    /** 
    * @param args 
    */ 
    public static void main(final String[] args) { 

     final Document doc = createDocument(); 
     final XPath xpath = createXpath(); 

     final NodeList xTimeStampNodes = findElements("//XTimeStamp/text()", 
       doc, xpath); 
     final Collection<String> xTimeStamps = convertToCollection(xTimeStampNodes); 

     final NodeList yVoltageNodes = findElements("//YVoltage/text()", doc, 
       xpath); 
     final Collection<String> yVoltages = convertToCollection(yVoltageNodes); 

     for (final String xTimeStamp : xTimeStamps) { 
      System.out.println("xTimeStamp: " + xTimeStamp); 
     } 
     for (final String yVoltage : yVoltages) { 
      System.out.println("yVoltage: " + yVoltage); 
     } 
    } 

    private static Document createDocument() { 
     Document doc = null; 
     try { 
      final DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory 
        .newInstance(); 
      documentBuilderFactory.setNamespaceAware(true); // never forget 
                  // this! 
      final DocumentBuilder builder = documentBuilderFactory 
        .newDocumentBuilder(); 
      doc = builder.parse(new ByteArrayInputStream(XMLSTRING 
        .getBytes("ISO-8859-1"))); 
     } catch (final UnsupportedEncodingException exception) { 
      // TODO handle exception 
     } catch (final SAXException exception) { 
      // TODO handle exception 
     } catch (final IOException exception) { 
      // TODO handle exception 
     } catch (final ParserConfigurationException exception) { 
      // TODO handle exception 
     } 
     return doc; 
    } 

    private static XPath createXpath() { 
     final XPathFactory xpathFactory = XPathFactory.newInstance(); 
     final XPath xpath = xpathFactory.newXPath(); 
     return xpath; 
    } 

    private static NodeList findElements(final String xpathExpression, 
      final Document doc, final XPath xpath) { 
     NodeList nodes = null; 
     if (doc != null) { 
      try { 
       final XPathExpression expr = xpath.compile(xpathExpression); 
       final Object result = expr 
         .evaluate(doc, XPathConstants.NODESET); 
       nodes = (NodeList) result; 
      } catch (final XPathExpressionException exception) { 
       // TODO handle exception 
      } 
     } 
     return nodes; 
    } 

    private static Collection<String> convertToCollection(final NodeList nodes) { 
     final Collection<String> result = new ArrayList<String>(); 
     if (nodes != null) { 
      for (int i = 0; i < nodes.getLength(); i++) { 
       result.add(nodes.item(i).getNodeValue()); 
      } 
     } 
     return result; 
    } 

}