SAXParseException：'Attribute＆＃8220;＆＃8221;绑定到命名空间＆＃8220; null＆＃8221;已经为元素指定＆＃8220; metric＆＃8221;'

Question

在工作中，我们刚刚将一个旧的web应用程序从struts 1.1迁移到1.2.9（希望第一步转移到1.3），但我们现在遇到了公共消化器的问题。 Struts 1.2.9使用commons-digester 1.6。

当我们尝试解析一个XML文件时，我们得到了异常：

org.xml.sax.SAXParseException: Attribute "" bound to namespace "null" was already specified for element "metric".
    at org.apache.xerces.util.ErrorHandlerWrapper.createSAXParseException(ErrorHandlerWrapper.java:232)
    at org.apache.xerces.util.ErrorHandlerWrapper.fatalError(ErrorHandlerWrapper.java:213)
    at org.apache.xerces.impl.XMLErrorReporter.reportError(XMLErrorReporter.java:385)
    at org.apache.xerces.impl.XMLErrorReporter.reportError(XMLErrorReporter.java:315)
    at org.apache.xerces.impl.dtd.XMLNSDTDValidator.startNamespaceScope(XMLNSDTDValidator.java:242)
    at org.apache.xerces.impl.dtd.XMLDTDValidator.handleStartElement(XMLDTDValidator.java:1980)
    at org.apache.xerces.impl.dtd.XMLDTDValidator.startElement(XMLDTDValidator.java:802)
    at org.apache.xerces.impl.XMLNSDocumentScannerImpl.scanStartElement(XMLNSDocumentScannerImpl.java:313)
    at org.apache.xerces.impl.XMLNSDocumentScannerImpl$NSContentDispatcher.scanRootElementHook(XMLNSDocumentScannerImpl.java:610)
    at org.apache.xerces.impl.XMLDocumentFragmentScannerImpl$FragmentContentDispatcher.dispatch(XMLDocumentFragmentScannerImpl.java:1608)
    at org.apache.xerces.impl.XMLDocumentFragmentScannerImpl.scanDocument(XMLDocumentFragmentScannerImpl.java:346)
    at org.apache.xerces.parsers.DTDConfiguration.parse(DTDConfiguration.java:529)
    at org.apache.xerces.parsers.DTDConfiguration.parse(DTDConfiguration.java:585)
    at org.apache.xerces.parsers.XMLParser.parse(XMLParser.java:152)
    at org.apache.xerces.parsers.AbstractSAXParser.parse(AbstractSAXParser.java:1142)
    at org.apache.commons.digester.Digester.parse(Digester.java:1572)
    at com.foo.ctms.framework.metrics.parser.MetricsXMLParser$InternalDigester.parse(MetricsXMLParser.java:54)
    at com.foo.ctms.framework.metrics.parser.MetricsXMLParser.parse(MetricsXMLParser.java:40)

在调查这个问题时，我试图找到一个最简单的案例，这就是我现在所拥有的：

package com.foo.ctms.framework.metrics.parser;

import org.apache.commons.digester.Digester;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;

import java.io.IOException;
import java.net.URL;

/**
 * Class that provides methods for parsing metrics definitions defined via XML and populating an object graph of JavaBeans
 * representing the definition.
 * @version $Revision: 41470 $
 */
public final class MetricsXMLParser {
  /**
   * The set of public identifiers, and corresponding resource names, for the versions of the configuration file DTD that we know
   * about.  The key is the name of the resource as in the XMl file, and the value is the location of the resource with respect to
   * the <code>ClassLoader</code> that this code in running in.
   */
  private static final String registrations[] = {"-//Foo Inc.//DTD Portal Metrics 1.0//EN", "metrics.dtd"};

  private MetricsXMLParser() {
  }

  /**
   * Parses a metric definition specified as an <code>InputStream</code>.
   * @param url The metrics definition to parse. Must not be <code>null</code>.
   * @throws IOException  if an I/O error occured while attempting to parse
   * @throws SAXException if an XML parsing error occured
   */
  public static MetricDefinition parse(URL url)
          throws IOException, SAXException {
    InternalDigester digester = new InternalDigester();
    return digester.parse(url);
  }

  private static final class InternalDigester {
    private final Digester digester;

    /**
     * Parses a metric definition specified as an <code>InputStream</code>.
     * @param input The metrics definition to parse. Must not be <code>null</code>.
     * @throws IOException  if an I/O error occured while attempting to parse
     * @throws SAXException if an XML parsing error occured
     */
    public MetricDefinition parse(URL input)
            throws IOException, SAXException {
      return (MetricDefinition)digester.parse(new InputSource(input.toString()));
    }

    private InternalDigester() {
      digester = new Digester();
      digester.setValidating(true);
      for (int i = 0; i < MetricsXMLParser.registrations.length; i += 2) {
        URL url = getClass().getResource(MetricsXMLParser.registrations[i + 1]);
        if (url != null) {
          digester.register(MetricsXMLParser.registrations[i], url.toString());
        }
      }

      digester.addObjectCreate("metric", MetricDefinition.class);
      digester.addSetProperties("metric");
    }
  }
}

给出了XML：

<?xml version='1.0' encoding='windows-1252'?>
<!DOCTYPE metric PUBLIC "-//Foo Inc.//DTD Portal Metrics 1.0//EN" "metrics.dtd">

<metric name="metricsConfig" defaultView="trials">

</metric>

DTD目前属于：     

<!-- A metric element is the document root -->
<!ELEMENT metric ANY>

<!-- A metric has a name and a default view.  The default view must
     exactly match the name of one of the nested views -->
<!ATTLIST metric
    name CDATA #REQUIRED
    defaultView CDATA #IMPLIED
>

有谁知道我做错了什么？

如果我删除defaultView属性，我不会收到错误。

---

根据sfussenegger的建议，我现在尝试了以下（非消化池）代码：

try {
  SAXParserFactory factory = SAXParserFactory.newInstance();
  factory.setNamespaceAware(false);
  factory.setValidating(true);
  SAXParser parser = factory.newSAXParser();
  XMLReader reader = parser.getXMLReader();
  reader.parse(new InputSource(url.toString()));
} catch (Exception e) {
  e.printStackTrace();
}

并且无法重现问题，但在使用我的工厂之前添加以下（在XercesParser中也使用了commons-digester）会产生相同的异常：

factory.setFeature("http://apache.org/xml/features/validation/dynamic", true);
factory.setFeature("http://apache.org/xml/features/validation/schema", true);

最后我们决定试用一个更现代的xerces版本（2.7.1），这似乎有效。

Answer 1

问题似乎是由于commons-digester 1.6和xerces之间不兼容（在XercesParser中称为2.2），转移到更新版本的xerces（2.7.1）已经解决了这个问题。

我们选择了这个版本的库，因为我们已经使用了其他Web应用程序。