使用 StAX 读取所有文本元素

Question

我需要解析一个 xml 文件，无论其中的标签如何，并读取其所有叶子的文本（仅限文本元素）。我正在使用 StAX，但似乎无法提前知道元素是否仅为文本（因此 getElementText 为 not leave 元素引发异常）。所以我决定使用过滤器，只过滤标签元素，并以这种方式迭代抛出文档：

InputStream in = null;
    try {
        in = new FileInputStream("file.xml");
        DatiEstratti de = DatiEstratti.getInstance();

        // Processamento ad eventi
        XMLInputFactory factory = (XMLInputFactory) XMLInputFactory.newInstance();

        XMLEventReader eventReader = factory.createXMLEventReader(in);
        // usa il filtro per filtrare solo i tag element
        eventReader = factory.createFilteredReader(eventReader, new ElementOnlyFilter());

        while (eventReader.hasNext()) {

            XMLEvent event = eventReader.nextEvent();

            if (event.getEventType() == XMLStreamConstants.START_ELEMENT) {
                StartElement startElement = event.asStartElement();

                XMLEvent peekEvent = eventReader.peek();
                if(peekEvent.isEndElement()){
                    // questa è la prima volta che viene fatto un pop
                    // quindi è una foglia.
                    // recupera il dato.
                    String value = eventReader.getElementText();

                    logger.info("dato : " + value);
                }


                String nome = startElement.getName().getLocalPart();
                String prefix = startElement.getName().getPrefix();
                if (prefix != null) {
                    nome = prefix + ":" + nome;
                }
                de.push(nome);
                logger.info("push : " + de.stampaPercorso());



            } else if ((event.getEventType() == XMLStreamConstants.END_ELEMENT)) {

                de.pop();
                logger.info("pop : " + de.stampaPercorso());
                if (0 > de.nLivelliPercorso()) {
                    break;
                }
            }
            //handle more event types here...
        }

...过滤器在哪里：

public class ElementOnlyFilter implements EventFilter, StreamFilter {

/* implementation of EventFilter interface */
@Override
public boolean accept(XMLEvent event) {
    return acceptInternal(event.getEventType(  ));
}

/* implementation of StreamFilter interface */
@Override
public boolean accept(XMLStreamReader reader) {
    return acceptInternal(reader.getEventType(  ));
}

/* internal utility method */
private boolean acceptInternal(int eventType) {
    return eventType == XMLStreamConstants.START_ELEMENT
            || eventType == XMLStreamConstants.END_ELEMENT;
}

}

问题是我在找到休假时遇到以下异常：

    javax.xml.stream.XMLStreamException: ParseError at [row,col]:[3,42]
Message: parser must be on START_ELEMENT to read next text
    at com.sun.xml.internal.stream.XMLEventReaderImpl.getElementText(XMLEventReaderImpl.java:114)
    at javax.xml.stream.util.EventReaderDelegate.getElementText(EventReaderDelegate.java:88)
    at xmlparser.XmlParser.main(XmlParser.java:63)

我想知道方法。这段代码有问题吗？我认为 peek() 不会改变阅读器，所以 getElementText() 应该由开始元素调用。还有其他方法可以实现我的目标吗？

Answer 1

首先，如果您过滤以仅包含开始和结束元素事件，那么您将根本看不到叶节点中包含的文本。我会使用不同的方法，使用未经过滤的流，如下所示：

XMLEventReader eventReader = factory.createXMLEventReader(in);
StringBuilder content = null;
while(eventReader.hasNext()) {
  XMLEvent event = eventReader.nextEvent();
  if(event.isStartElement()) {
    // other start element processing here
    content = new StringBuilder();
  } else if(event.isEndElement()) {
    if(content != null) {
      // this was a leaf element
      String leafText = content.toString();
      // do something with the leaf node
    } else {
      // not a leaf
    }
    // in all cases, discard content
    content = null;
  } else if(event.isCharacters()) {
    if(content != null) {
      content.append(event.asCharacters().getData());
    }
  }
  // other event types here
}

诀窍是content = null在结束元素部分的末尾 - 在if(event.isEndElement())块的入口处，如果content非空，那么你知道在这个和它相应的开始标签之间没有中间的结束元素事件，即它是一个叶节点。