java - XPathReader 错误 : java. lang.String 无法转换为 org.w3c.dom.Node

Question

我正在尝试解析从 Clob 类型获取的 XML 数据。由于某种原因，我遇到了这个异常......我不明白为什么。我从 Oracle 数据库列中获取了 Clob，其中包含 XMLType 值，即 XML。我已成功将 XMLType 中包含的 XML 提取为 Clob 类型。这是通过以下代码获得的:

xmlBean =  XmlHelper.xPathRead(film.getXmlClob());

如果您愿意的话，film 对象位于模型中，并且 getXmlClob() 方法返回一个 Clob 值，其中包含我想要使用 XPath 解析的 XML。这是其余的代码:

XMLHelper

public static XmlBean xPathRead(Clob xmlClob) {
    XPathReader reader = new XPathReader(xmlClob);
    XmlBean xmlBean = new XmlBean();   // just an entity from the model to store the xml's contents inside

    String filmId = "/IMAGE[1]/@id";
    xmlBean.setFilmId(Integer.parseInt((String) reader.read(filmId, XPathConstants.STRING)));
}

XPathReader

public class XPathReader {
    private String xmlString;
    private XPath xPath;

    public XPathReader(Clob xmlClob) {

        try {
            if ((int) xmlClob.length() > 0) {  
                String s = xmlClob.getSubString(1, (int) xmlClob.length()); // this is a way to cast a CLOB into a STRING
                this.xmlString = s;
              }
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        xPath = XPathFactory.newInstance().newXPath();
    }

    public Object read(String expression, QName returnType) {
        try {
            XPathExpression xPathExpression = xPath.compile(expression);
            return xPathExpression.evaluate(xmlString, returnType);
        } catch (XPathExpressionException ex) {
            ex.printStackTrace();
            return null;
        }
    }
}

有什么想法吗？问题出在 evaluate() 方法中...

错误消息

java.lang.ClassCastException: java.lang.String cannot be cast to org.w3c.dom.Node at com.sun.org.apache.xpath.internal.jaxp.XPathExpressionImpl.eval(Unknown Source) at com.sun.org.apache.xpath.internal.jaxp.XPathExpressionImpl.eval(Unknown Source) at com.sun.org.apache.xpath.internal.jaxp.XPathExpressionImpl.evaluate(Unknown Source) at helper.XPathReader.read(XPathReader.java:34) at helper.XmlHelper.xPathRead(XmlHelper.java:325)

Answer 1

无论如何你都不能通过字符串来做到这一点。

像这样怎么样

public class XPathReader {
  private XPath xPath;
  private Document doc;

  public XPathReader(Clob xmlClob) {

    try {
        if ((int) xmlClob.length() > 0) {  
            String s = xmlClob.getSubString(1, (int) xmlClob.length()); // this is a way to cast a CLOB into a STRING
            doc = readDoc(s);
          }
    } catch (SQLException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    xPath = XPathFactory.newInstance().newXPath();
}

public Object read(String expression, QName returnType) {
    try {
        XPathExpression xPathExpression = xPath.compile(expression);
        return xPathExpression.evaluate(doc, returnType);
    } catch (XPathExpressionException ex) {
        ex.printStackTrace();
        return null;
    }
}

public Document readDoc(String s)
{
    Document d = null;
    try
    {
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        DocumentBuilder builder = factory.newDocumentBuilder();
        InputSource is = new InputSource(new StringReader(s));
        d = builder.parse(is);
    } catch (Exception e)
    {
    }
    return d;
}

}

我还没有真正尝试过，你需要更好的错误处理，但它应该可以正常工作