java.lang.ClassCastException：错误

Question

这是给出一些货币的 XML 文件 sn-p。它们都具有“货币名称”、“外汇购买”、“外汇销售”等值......

<?xml version="1.0" encoding="UTF-8"?>

<Currency CrossOrder="1" Kod="AUD" CurrencyCode="AUD">
        <Unit>1</Unit>
        <Isim>AVUSTRALYA DOLARI</Isim>
        <CurrencyName>AUSTRALIAN DOLLAR</CurrencyName>
        <ForexBuying>4.4233</ForexBuying>
        <ForexSelling>4.4521</ForexSelling>
        <BanknoteBuying>4.4030</BanknoteBuying>
        <BanknoteSelling>4.4789</BanknoteSelling>
        <CrossRateUSD>1.3839</CrossRateUSD>
        <CrossRateOther/>
    </Currency>

<Currency CrossOrder="2" Kod="DKK" CurrencyCode="DKK">
        <Unit>1</Unit>
        <Isim>DANIMARKA KRONU</Isim>
        <CurrencyName>DANISH KRONE</CurrencyName>
        <ForexBuying>0.93070</ForexBuying>
        <ForexSelling>0.93527</ForexSelling>
        <BanknoteBuying>0.93004</BanknoteBuying>
        <BanknoteSelling>0.93742</BanknoteSelling>
        <CrossRateUSD>6.5827</CrossRateUSD>
        <CrossRateOther/>
    </Currency>

这是我的实际代码：

import javax.lang.model.element.Element;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import java.io.*;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

public class PasteClass {

    public static void main(String[] args) {

        try {
            File xmlFile = new File("TCMB2.xml");
            DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
            DocumentBuilder documentBuilder = documentBuilderFactory.newDocumentBuilder();
            org.w3c.dom.Document document = documentBuilder.parse(xmlFile);
            NodeList list = document.getElementsByTagName("Currency");

            for (int i = 0; i < list.getLength(); i++) {

                Node node = list.item(i);

                if (node.getNodeType() == Node.ELEMENT_NODE) {
                    Element element = (Element) node;
                    System.out.println("Kod: "
                            + ((org.w3c.dom.Document) element)
                                .getElementsByTagName("Kod").item(0).getTextContent());
                    System.out.println("Para Birimi: "
                            + ((org.w3c.dom.Document) element)
                                .getElementsByTagName("Isim").item(0).getTextContent());
                    System.out.println("Forex Satis Ucreti: " 
                            + ((org.w3c.dom.Document) element)
                                .getElementsByTagName("ForexSelling").item(0).getTextContent());
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

}

我想做的是，简单地从 XML 文件中获取一些数据。这是我第一次使用 XML。我只希望它为每个元素打印“kod”、“Isim”和“forex Selling”值。但是当我运行代码时，我得到了这个错误：

java.lang.ClassCastException：java.xml/com.sun.org.apache.xerces.internal.dom.DeferredElementImpl 无法转换为 java.compiler/javax.lang.model.element.Element 在 javaPaket.WONTWORK.main(WONTWORK.java:36)

（第36行是“元素元素=（元素）节点；”顺便说一句。）

我该如何解决这个问题？我从另一个站点复制了类似的代码，只是更改了值。然而我得到了这个错误.....

Answer 1

你会尝试运行下面的代码吗？仅更改了 for 块中的代码。

public static void main(String[] args) {

    try {

        File xmlFile = new File("TCMB2.xml");
        DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
        DocumentBuilder documentBuilder = documentBuilderFactory.newDocumentBuilder();
        org.w3c.dom.Document doc = documentBuilder.parse(xmlFile);

        NodeList list = doc.getElementsByTagName("Currency");


        for (int i = 0; i < list.getLength(); i++) {

            Node node = list.item(i);

            if (node.getNodeType() == Node.ELEMENT_NODE) {
                Element element = (Element) node;
                System.out.println("Kod: " + element.getAttribute("Kod"));
                System.out.println("Para Birimi: " + element.getElementsByTagName("Isim").item(0).getTextContent());
                System.out.println("Forex Satis Ucreti: " + element.getElementsByTagName("ForexSelling").item(0).getTextContent()) ;

            }
        }

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

样本输出：

Kod：澳元
Para Birimi: AVUSTRALYA DOLARI
外汇 Satis Ucreti：4.4521
科德：丹麦克朗
帕拉比里米：DANIMARKA KRONU
外汇 Satis Ucreti：0.93527

Answer 2

问题是您的导入不正确

import javax.lang.model.element.Element;

和

不一样

import org.w3c.dom.Element;

这会导致您的 java 代码发生冲突。 试试这个 Imports：

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import java.io.*;

import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

做一个简单的例子并且正在工作。

---

尝试清理并重新构建您的代码。

在最坏的情况下试试这个

  org.w3c.dom.Element element = (org.w3c.dom.Element) node;

Answer 3

我认为你应该这样做：

Element element = (org.w3c.dom.Element) node;

因为您还导入了 javax.lang.model.element.Element，并且我怀疑该类型正在发生转换（正如堆栈跟踪本身所暗示的那样）。

Answer 4

好的，您的代码存在一些问题，涉及人们已经提出的导入，但您还需要对代码进行一些其他更改，以使其按照您想要的方式工作。

首先这里是我正在使用的 XML，您没有弄乱代码的根元素，但您确实说这不是您使用的完整文件，所以我不确定您是否需要查看它.

Test.xml：

<root>
    <Currency CrossOrder="1" Kod="AUD" CurrencyCode="AUD">
            <Unit>1</Unit>
            <Isim>AVUSTRALYA DOLARI</Isim>
            <CurrencyName>AUSTRALIAN DOLLAR</CurrencyName>
            <ForexBuying>4.4233</ForexBuying>
            <ForexSelling>4.4521</ForexSelling>
            <BanknoteBuying>4.4030</BanknoteBuying>
            <BanknoteSelling>4.4789</BanknoteSelling>
            <CrossRateUSD>1.3839</CrossRateUSD>
            <CrossRateOther/>
    </Currency>

    <Currency CrossOrder="2" Kod="DKK" CurrencyCode="DKK">
            <Unit>1</Unit>
            <Isim>DANIMARKA KRONU</Isim>
            <CurrencyName>DANISH KRONE</CurrencyName>
            <ForexBuying>0.93070</ForexBuying>
            <ForexSelling>0.93527</ForexSelling>
            <BanknoteBuying>0.93004</BanknoteBuying>
            <BanknoteSelling>0.93742</BanknoteSelling>
            <CrossRateUSD>6.5827</CrossRateUSD>
            <CrossRateOther/>
    </Currency>
</root>

这是解析 XML 的 Java：

    import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import java.io.*;
import java.util.HashMap;

import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
public class Test{

    public static void main(String[] args) {

         /* 
        These are the values for the xml lines based on your file
        Unit            = 1
        Isim            = 2
        CurrencyName    = 3 
        ForexBuying     = 4
        ForexSelling    = 5
        BanknoteBuying  = 6
        BanknoteSelling = 7
        CrossRateUSD    = 8
         */

        //create a HashMap to map the loop count to the proper name
        //while printing, these are based on numbers commented above
        HashMap<Integer, String> mapOfItems = new HashMap<>();
        mapOfItems.put(1, "Unit");
        mapOfItems.put(2, "Isim");
        mapOfItems.put(3, "CurrencyName");
        mapOfItems.put(4, "ForexBuying");
        mapOfItems.put(5, "ForexSelling");
        mapOfItems.put(6, "BanknoteBuying");
        mapOfItems.put(7, "BanknoteSelling");
        mapOfItems.put(8, "CrossRateUSD");  

        try {
            File xmlFile = new File("test.xml");
            DocumentBuilderFactory documentBuilderFactory = 
                    DocumentBuilderFactory.newInstance();

            DocumentBuilder documentBuilder =  
                    documentBuilderFactory.newDocumentBuilder();

            org.w3c.dom.Document document = 
                    documentBuilder.parse(xmlFile);

            NodeList list = document.getElementsByTagName("Currency");

            for(int i=0;i<list.getLength();i++) {

                Node node = list.item(i);

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

                    //gather node with specific attribute, here item(2) == Kod 
                    String kodValue = node.getAttributes().item(2).getTextContent();

                    //create array based on text content, split be new line    
                    String[] values = node.getTextContent().split("\n");

                        System.out.println("\nKOD = "+ kodValue);
                        for (Integer e = 0; e < values.length; e++) {

                            //replaceAll() is for regex replacement of white space here
                            values[e] = values[e].replaceAll(
                                    "^\\s+|\\s+$|\\s*(\n)\\s*|(\\s)\\s*", "$1$2")
                                     .replace("\t"," ");

                            //just check to make sure null isn't being printed
                            if(mapOfItems.get(e)!= null)
                                System.out.println(mapOfItems.get(e)+" = "+values[e]);
                        }
                    }
                }
        }
        catch(Exception e) {
            e.printStackTrace();
        }
    }
}