使用Commons JXPath进行XML解析的问题

Question

我正在尝试使用Apache Commons JXPath解析XML。但是由于某种原因，它不能在解析xml后识别子节点。下面是示例代码:

private static void processUrl(String seed){
    String test = "<?xml version="1.0" encoding="UTF-8"?><feed xmlns="http://www.w3.org/2005/Atom" xmlns:media="http://search.yahoo.com/mrss/" xmlns:openSearch="http://a9.com/-/spec/opensearchrss/1.0/" xmlns:gd="http://schemas.google.com/g/2005" xmlns:yt="http://gdata.youtube.com/schemas/2007"><id>http://gdata.youtube.com/feeds/api/videos</id><logo>http://www.youtube.com/img/pic_youtubelogo_123x63.gif</logo><link rel="alternate" type="text/html" href="http://www.youtube.com"/><author><name>YouTube</name><uri>http://www.youtube.com/</uri></author><generator version="2.1" uri="http://gdata.youtube.com">YouTube data API</generator><openSearch:totalResults>144</openSearch:totalResults><entry><id>http://gdata.youtube.com/feeds/api/videos/P1lDDu9L5YQ</id><published>2010-09-20T17:41:38.000Z</published><updated>2011-09-18T22:15:38.000Z</updated><category scheme="http://schemas.google.com/g/2005#kind" term="http://gdata.youtube.com/schemas/2007#video"/><link rel="alternate" type="text/html" href="http://www.youtube.com/watch?v=P1lDDu9L5YQ&amp;feature=youtube_gdata"/></entry></feed>";
    Document doc = null;
    try{
        DocumentBuilder builder = DocumentBuilderFactory.newInstance().newDocumentBuilder();
        ByteArrayInputStream bais = new ByteArrayInputStream(test.toString().getBytes("UTF8"));
        doc = builder.parse(bais);
        bais.close();
        JXPathContext ctx = JXPathContext.newContext(doc);
        List entryNodes = ctx.selectNodes("/feed/entry");
        System.out.println("number of threadNodes " + entryNodes.size());
        int totalThreads = 0;
        for (Object each : entryNodes) {
            totalThreads++;
            Node eachEntryNode = (Node) each;
            JXPathContext msgCtx = JXPathContext.newContext(eachEntryNode);
            String title = (String) msgCtx.getValue("title");
        }
    }catch (Exception ex) {
        ex.printStackTrace();
    }
}

我以前使用过JXPath，从来没有遇到过任何问题。我调试了文档对象，它似乎没有子节点()for。我只能看到根元素。我还尝试了DOMParser，但没有任何运气。

DOMParser parser = new DOMParser();
        Document doc = (Document) parser.parseXML(new ByteArrayInputStream(sb0.toString().getBytes("UTF-8")));

Answer 1

这个问题与JXPath如何处理默认名称空间有关，这与XPath 1.0规范密切相关。这也解释了为什么在删除默认名称空间http://www.w3.org/2005/Atom之后它还能工作。为了让它与默认名称空间一起工作，您可以执行以下操作:

JXPathContext ctx = JXPathContext.newContext(doc.getDocumentElement());
// Register the default namespace, giving it a prefix of your choice
ctx.registerNamespace("myfeed", "http://www.w3.org/2005/Atom");
// Now query for entry elements using the registered prefix
List entryNodes = ctx.selectNodes("myfeed:entry");

有关该问题的更多信息，请参阅以下链接。

http://markmail.org/message/7iqw4bjrkwerbh46

让jxpath命名空间感知